User manual | Information Systems Technician Training Series

NONRESIDENT
TRAINING
COURSE
October 1997
Information Systems
Technician Training Series
Module 3—Network Communications
NAVEDTRA 14224
NOTICE
Any reference within this module to “Radioman” or the former
“Radioman rating” should be changed to “Information Systems
Technician” and the “Information Systems Technician (IT) rating”.
The subject matter presented relates to the occupational
standards for the IT rating.
DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
Although the words “he,” “him,” and
“his” are used sparingly in this course to
enhance communication, they are not
intended to be gender driven or to affront or
discriminate against anyone.
DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.
PREFACE
By enrolling in this self-study course, you have demonstrated a desire to improve yourself and the Navy.
Remember, however, this self-study course is only one part of the total Navy training program. Practical
experience, schools, selected reading, and your desire to succeed are also necessary to successfully round
out a fully meaningful training program.
COURSE OVERVIEW: In completing this nonresident training course, you will demonstrate a
knowledge of subject mattter by correctly answering questions on the following subjects: Network
Administration, LAN Hardware, and Network Troubleshooting.
THE COURSE: This self-study course is organized into subject matter areas, each containing learning
objectives to help you determine what you should learn along with text and illustrations to help you
understand the information. The subject matter reflects day-to-day requirements and experiences of
personnel in the rating or skill area. It also reflects guidance provided by Enlisted Community Managers
(ECMs) and other senior personnel, technical references, instructions, etc., and either the occupational or
naval standards, which are listed in the Manual of Navy Enlisted Manpower Personnel Classifications
and Occupational Standards, NAVPERS 18068.
THE QUESTIONS: The questions that appear in this course are designed to help you understand the
material in the text.
VALUE: In completing this course, you will improve your military and professional knowledge.
Importantly, it can also help you study for the Navy-wide advancement in rate examination. If you are
studying and discover a reference in the text to another publication for further information, look it up.
1997 Edition Prepared by
DPC(SW) Walter Shugar, Jr. and
RMCS(SW/AW) Deborah Hearn
Reissued on July 2002 to correct
minor discrepancies or update
information. No significant change
have been made to content.
Published by
NAVAL EDUCATION AND TRAINING
PROFESSIONAL DEVELOPMENT
AND TECHNOLOGY CENTER
NAVSUP Logistics Tracking Number
0504-LP-026-8630
i
Sailor’s Creed
“I am a United States Sailor.
I will support and defend the
Constitution of the United States of
America and I will obey the orders
of those appointed over me.
I represent the fighting spirit of the
Navy and those who have gone
before me to defend freedom and
democracy around the world.
I proudly serve my country’s Navy
combat team with honor, courage
and commitment.
I am committed to excellence and
the fair treatment of all.”
ii
CONTENTS
CHAPTER
PAGE
1. Network Administration . . . . . . . . . . . . . . . . . . . . . .1-1
2. LAN Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1
3. Network Troubleshooting. . . . . . . . . . . . . . . . . . . . . . 3-1
APPENDIX
I. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AI-1
II. Glossary of Acronyms and Abbreviations . . . . . . . . . . . . AII-1
III. References Used to Develop the TRAMAN. . . . . . . . . . . AIII-1
INDEX
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDEX-1
NONRESIDENT TRAINING COURSE follows the index
iii
SUMMARY OF THE RADIOMAN
TRAINING SERIES
MODULE 1
Administration and Security—This module covers Radioman duties relating to
administering AIS and communication systems. Procedures and guidance for
handling of classified information, messages, COMSEC material and equipment,
and AIS requirements are discussed.
MODULE 2
Computer Systems—This module covers computer hardware startup, including
peripheral operations and system modification. Other topics discussed include
computer center operations, media library functions, system operations, and
troubleshooting techniques. Data file processes, memory requirements, and
database management are also covered.
MODULE 3
Network Communications-This module covers network administration, LAN
hardware, and newtwork trobleshooting. Related areas discussed are network
configuration and operations, components and connections, and communication
lines and nodes.
MODULE 4
Communications Hardware—This module covers various types of
communications equipment, including satellites and antennas. Subjects discussed
include hardware setup procedures, COMSEC equipment requirements, distress
communications equipment, troubleshooting equipment, satellite theory, and
antenna selection and positioning.
MODULE 5
Communications Center Operations—This module covers center operations,
including transmit message systems, voice communications, center administration,
quality control, and circuit setup/restorations. Guidelines for setting EMCON and
HERO conditions and cryptosecurity requirements are also discussed.
iv
CREDITS
Trademark Credits
ARCnet is a registered trademark of Datapoint Corporation.
Ethernet is a registered trademark of Xerox Corporation.
Novell is a registered trademark of Novell, Inc.
UNIX is a registered trademark of X/Open Company Ltd.
Windows 3.11 is a registered trademark of Microsoft Corporation.
Windows 95 is a registered trademark of Microsoft Corporation.
Windows NT is a registered trademark of Microsoft Corporation.
v
INSTRUCTIONS FOR TAKING THE COURSE
assignments. To submit your
answers via the Internet, go to:
ASSIGNMENTS
The text pages that you are to study are listed at
the beginning of each assignment. Study these
pages carefully before attempting to answer the
questions. Pay close attention to tables and
illustrations and read the learning objectives.
The learning objectives state what you should be
able to do after studying the material. Answering
the questions correctly helps you accomplish the
objectives.
https://courses.cnet.navy.mil
Grading by Mail: When you submit answer
sheets by mail, send all of your assignments at
one time. Do NOT submit individual answer
sheets for grading. Mail all of your assignments
in an envelope, which you either provide
yourself or obtain from your nearest Educational
Services Officer (ESO). Submit answer sheets
to:
SELECTING YOUR ANSWERS
Read each question carefully, then select the
BEST answer. You may refer freely to the text.
The answers must be the result of your own
work and decisions. You are prohibited from
referring to or copying the answers of others and
from giving answers to anyone else taking the
course.
COMMANDING OFFICER
NETPDTC N331
6490 SAUFLEY FIELD ROAD
PENSACOLA FL 32559-5000
Answer Sheets: All courses include one
“scannable” answer sheet for each assignment.
These answer sheets are preprinted with your
SSN, name, assignment number, and course
number. Explanations for completing the answer
sheets are on the answer sheet.
SUBMITTING YOUR ASSIGNMENTS
To have your assignments graded, you must be
enrolled in the course with the Nonresident
Training Course Administration Branch at the
Naval Education and Training Professional
Development
and
Technology
Center
(NETPDTC). Following enrollment, there are
two ways of having your assignments graded:
(1) use the Internet to submit your assignments
as you complete them, or (2) send all the
assignments at one time by mail to NETPDTC.
Grading on the Internet:
Internet grading are:
•
•
assignment
Do not use answer sheet reproductions: Use
only the original answer sheets that we
provide—reproductions will not work with our
scanning equipment and cannot be processed.
Follow the instructions for marking your
answers on the answer sheet. Be sure that blocks
1, 2, and 3 are filled in correctly. This
information is necessary for your course to be
properly processed and for you to receive credit
for your work.
Advantages to
COMPLETION TIME
you may submit your answers as soon as
you complete an assignment, and
you get your results faster; usually by the
next working day (approximately 24 hours).
Courses must be completed within 12 months
from the date of enrollment. This includes time
required to resubmit failed assignments.
In addition to receiving grade results for each
assignment, you will receive course completion
confirmation once you have completed all the
vi
PASS/FAIL ASSIGNMENT PROCEDURES
For subject matter questions:
If your overall course score is 3.2 or higher, you
will pass the course and will not be required to
resubmit assignments. Once your assignments
have been graded you will receive course
completion confirmation.
E-mail:
Phone:
[email protected]
Comm: (850) 452-1501
DSN: 922-1501
FAX: (850) 452-1370
(Do not fax answer sheets.)
Address: COMMANDING OFFICER
NETPDTC N311
6490 SAUFLEY FIELD ROAD
PENSACOLA FL 32509-5237
If you receive less than a 3.2 on any assignment
and your overall course score is below 3.2, you
will be given the opportunity to resubmit failed
assignments. You may resubmit failed
assignments only once. Internet students will
receive notification when they have failed an
assignment--they may then resubmit failed
assignments on the web site. Internet students
may view and print results for failed
assignments from the web site. Students who
submit by mail will receive a failing result letter
and a new answer sheet for resubmission of each
failed assignment.
For enrollment, shipping,
completion letter questions
grading,
or
E-mail:
Phone:
[email protected]
Toll Free: 877-264-8583
Comm: (850) 452-1511/1181/1859
DSN: 922-1511/1181/1859
FAX: (850) 452-1370
(Do not fax answer sheets.)
Address: COMMANDING OFFICER
NETPDTC N331
6490 SAUFLEY FIELD ROAD
PENSACOLA FL 32559-5000
COMPLETION CONFIRMATION
After successfully completing this course, you
will receive a letter of completion.
NAVAL RESERVE RETIREMENT CREDIT
ERRATA
If you are a member of the Naval Reserve,
you may earn retirement points for successfully
completing this course, if authorized under
current directives governing retirement of Naval
Reserve personnel. For Naval Reserve retirement, this course is evaluated at 3 points. (Refer
to Administrative Procedures for Naval
Reservists on Inactive Duty, BUPERSINST
1001.39, for more information about retirement
points.)
Errata are used to correct minor errors or delete
obsolete information in a course. Errata may
also be used to provide instructions to the
student. If a course has an errata, it will be
included as the first page(s) after the front cover.
Errata for all courses can be accessed and
viewed/downloaded at:
https://www.advancement.cnet.navy.mil
STUDENT FEEDBACK QUESTIONS
We value your suggestions, questions, and
criticisms on our courses. If you would like to
communicate with us regarding this course, we
encourage you, if possible, to use e-mail. If you
write or fax, please use a copy of the Student
Comment form that follows this page.
vii
Student Comments
Course Title:
Information Systems Technician Training Series
Module 3—Network Communications
NAVEDTRA:
14224
Date:
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NETPDTC 1550/41 (Rev 4-00
ix
CHAPTER 1
NETWORK ADMINISTRATION
Upon completing this chapter, you should be able to do the following:
Describe how to establish communications with remote terminals and
monitor system transmissions.
Describe how to start up, monitor, and terminate network processing.
Explain how to change network software configurations and how to analyze
network hardware configurations.
Explain how to install and test software and how to perform system
restorations.
Explain how to evaluate network requests.
Describe the procedures used to calculate network capacity.
Explain how to determine communications protocols and how to design a
network.
relatively small geographical area, commonly known as
a local area network, ranging from a few feet to a mile.
Nodes are the hardware, such as computers, terminals,
hard disks, printers, and so on. Links are the
communications media, such as twisted-pair wire,
coaxial cable, or fiber optic cable that connects the
nodes.
Welcome to the wonderful world of networking.
Networking has opened the world to connectivity.
Networking gives an individual the capability to
communicate and connect with another individual or
another system in order to share resources.
The end result is to establish communications
between two PC computers or two entirely different
systems. The process used to reach that point can be
done many ways. Once you have established
connectivity and are communicating, then you will
need to monitor the systems transmission to ensure the
two computers are, in fact, communicating
successfully. Some of the factors that will have to be
taken into consideration are:
Networks are made up of a variety of hardware,
network software, connecting cables, and network
interface cards combined in any number of ways. And
that is perfectly OK. Quite often, we design a network
using existing hardware. That is just one of the many
reasons why each individual network has its own
unique characteristics. The network hardware and
software components determine the structure of a
network, whether it is a local, metropolitan, or wide area
network. Normally, the workstations (PCs) in a LAN
are in close proximity to each other, usually within the
same building. A metropolitan area network (MAN)
consists of PCs that are basewide: one command
connected with another command, or one base
connected with another base, all via phone lines. A wide
area network (WAN) is worldwide: one country
connected with another country via satellites, etc.
What type of hardware will be needed
What operating system (OS) will be used
What applications will be needed
What type of cabling will be used
NETWORK OPERATIONS
Networks consist of nodes that are interconnected
by links. These nodes and links usually cover a
1-1
remote console. The remote capabilities will increase
productivity. The network supervisor can manage the
system by establishing communications through a
remote terminal.
A network could be made up of 13 PCs, a server
with a hard disk, 3 printers, and a plotter. Another
network could be made up of 6 PCs (one of which is the
network server) and a laser printer. Both are networks.
When you connect individual PCs together (via cable),
and each PC is allowed access to the other’s information
and/or resources, you have created a network (see figure
1-1). By connecting PCs in this fashion, you are able to
share all sorts of things. Examples are information in
files; software, such as word processors, spreadsheet
programs, and utilities; and peripheral devices, such as
hard disks, printers, plotters, and fax machines.
Logins from Remote Locations
Remote access refers to logins from remote
locations. These login procedures are accomplished by
dialing into an access server (a special modem or
computer) and logging in through this server.
The network modems that can be used as remote
access servers must have a network interface card (NIC)
compatible with the network to which the modem is
providing access. Remote connections often require
special timing considerations, because many network
transactions must happen within a very limited time
period.
A network gives you the capability of transferring
data, files, programs, you name it, from one PC to
another or even from one network to another. You can
transfer a report or listing to any printer you desire on
the network, provided you have access to the printer.
How is that for flexibility? By connecting your PC into
a network system, you can execute application
programs stored on the server’s hard disk without
having to worry about disk space or keeping track of
diskettes. You can exchange files and programs with
other users directly without copying them onto a
diskette. Can you begin to see the power and flexibility
built into a network system?
Remote Console
A networking utility that enables a network
supervisor to manage a server from a workstation or
from a remote location using a modem. The supervisor
can give commands and accomplish tasks just as if all
the commands were being given directly at the server by
simulating a direct connection to the server.
COMMUNICATIONS WITH REMOTE
TERMINALS
NETWORK STARTUP/SHUTDOWN
The ability to connect to the LAN through the use of
remote terminals gives you great flexibility, whether it
is being able to check your E-mail via a modem or check
the status of the LAN by connecting to the network as a
Keeping the system running is the most visible
aspect of system administration. You’re the one they
will call when the system has gone down (crashed). We
will discuss the normal UNIX booting (startup) and
shutdown processes. Shutting down and bringing up a
UNIX system is actually very simple.
System Startup
Every time the system is booted, a series of steps
must be performed before the system becomes available
to users. Booting is the process of bringing a computer
system up and making it ready to use.
The process begins when some instructions stored
in ROM are executed which load the program boot from
the boot partition into system memory. Boot loads the
bootable operating system, which is also called the
bootable kernel. The bootable kernel starts the init
(initialization) program.
INIT.— One of the first things init does is check
available memory, Next, it checks out the environment
to see what hardware is present. When the kernel is
Figure 1-1.—Connecting PCs to form a local area network.
1-2
configured, it is told what types of hardware devices to
expect. Init will search for and attempt to initialize each
physically attached device. Any device that does not
initialize or that is missing will be marked as
nonexistent and the driver disabled. Even if the device
is later reconnected, it will be unusable until the system
is rebooted.
If you make changes to any of the system
software or configuration files that are examined
or executed only when the system is booted, you
must reboot for these changes to take effect.
Some devices, especially printer and modem
ports, can become confused enough that
resetting them is only accomplished by reinitializing the system.
When all is ready, the kernel verifies the integrity of
the root filesystem and then mounts it. Init does the rest
of the work that is needed in preparing the system for
users. This includes mounting the remaining local disk
partitions (those found in the file /etc/checklist);
performing some filesystem cleanup operations (fsck);
turning on the major UNIX subsystems, such as
accounting and the print service; starting the network;
mounting remote file systems; and enabling user logins.
If the system has been up and running constantly
for over a week, it is wise to bring the system
down to single-user mode and run fsck. If any
fixes are made to the root partition, the system
must be rebooted.
If the system console becomes irretrievably
hung, the system must be rebooted.
SYSTEM MODES.— There are two primary
modes of system operation: single-user and multi-user.
Single-user is a system state designed for administrative
and maintenance activities which require complete and
unshared control of the system. Single-user mode is
sometimes called the maintenance mode. Single-user
mode is entered via manual intervention during the boot
process. Sometimes, however, the system will enter
single-user mode if there are problems in the boot
process that the system cannot handle on its own.
Multi-user allows many users to all log onto the same
CPU. Users can access different applications
simultaneously or even the same application
simultaneously. The kernel manages the different users
by scheduling the use of the processing time as well as
swapping programs and data in and out of memory
through virtual memory to disk. The most important
fact to remember is that the number of concurrent users
depends on the amount of memory installed in the
computer. Each user has a certain amount of memory
set aside for his or her work, unless everyone is willing
to tolerate slow response time from the network.
SHUTTING THE SYSTEM DOWN.— There are
two proper ways to shut down the operating system:
shutdown and reboot. As a last resort, the system can be
shut down by turning off the power to the CPU. This
method is recommended only under emergency
conditions because of its detrimental impact on system
files and certain types of hard disk drives. These disk
drives expect their floating heads to be parked prior to
shutdown. Powering off the system could cause the
heads to crash and cause irreparable damage to the disk.
Shutdown.— This command is the most often used
method of initiating a orderly system shutdown. It is the
safest, most considerate, and most thorough to initiate a
halt, reboot, or return to single-user mode. The
command will send messages to each user’s terminal at
progressively shorter intervals as the time for shutdown
approaches. The messages tell the time of the
shutdown.
Reboot.— This command terminates all currently
executing processes except those essential to the
system, then halts or reboots the system. When invoked
without arguments, reboot syncs all disks before
rebooting the system. The command does not send a
message out to the users, unless you use the message
option.
System Shutdown
While there are many occasions when shutting
down or rebooting the system is appropriate, neither
operation should be performed indiscriminantly. While
it is generally not something to worry about, there is a
degree of hardware fatigue associated with turning a
computer system off and on again, and it is often better
to let it run 24 hours a day than to shut it down at night.
MONITOR
Some people would ask, “Why do I have to expend
energy on monitoring the network when I could be
doing something more productive, like file server or
workstation maintenance?” There are several reasons
why you should monitor your network:
REBOOTING.— There are only four common
situations in which rebooting the system is called for:
1-3
Because of equipment compatibility and
interoperability, a system administrator needs to know
considerable detail about all of the equipment that
comprises the network. This information may include
model numbers, memory specifications, enhancements,
and so on. This information must be maintained, or
conflicts between the equipment may occur. Most
networking systems include a utility for recording
system configuration information and updating it as the
net work changes.
To maintain a history of the performance of your
system. Studying this history could point out
potential failures long before they occur.
To provide a statistical basis for new equipment
requests. Management is more likely to purchase
new equipment if you can demonstrate that the
current equipment will not meet the company’s
needs.
To enable you to tune your network for optimum
performance. This is especially true on larger
networks with more than one file server. In some
cases, you can provide a perceived increase in
throughput by simply transferring tasks from one
server to another.
Record the current settings for each component as
part of the configuration information. Avoid conflicts
when deciding on specific settings. A conflict can arise
because two boards want to use the same memory
location or interrupt.
Various network operating systems (NOSs) have
their own utility programs to monitor what processing is
taking place on their network. You can use these
programs to monitor the status of your network, and
some utilities give you the capability to monitor a
particular job request.
SYSTEM PARAMETERS
System parameters must be verified prior to
installation and startup to avoid any conflicts. The
majority of the conflicts involve system interrupts. An
interrupt is a mechanism by which one computing
element, such as a modem or a program, can get the
attention of another elements. Interrupts may be
generated by hardware or software.
REVIEW AUDIT LOGS
The main importance of reviewing audit/event logs
is to monitor the security of the system. Besides, C2
Security compliance requires that the system be
monitored (audited) continuously. Whether it pertains
to the system – what hardware was accessed, security –
identify who logged on (logged-in), or application –
what software was accessed; usage must be tracked.
Hardware Interrupt
There are 16 interrupt request lines (IRQs) for
hardware interrupts in a PC environment. Each device
attached to a computer can have an IRQ assigned.
When the device wants service from the CPU, it signals
on this line and waits.
The term auditing refers to the process of recording
events, such as file access, creations, deletions, the
addition of print jobs, and so on, and using that
information to detect usage violations or to confirm that
network procedures are operating correctly.
IRQs have different priority levels, and the higher
priority lines are assigned to the most important
functions on the PC. By responding to IRQs according
to their assigned priority, an operating system or
interrupt handler can ensure that no vital activities are
interrupted.
A network administrator, by using the audit logs,
can track what files were accessed, when they were
accessed (date and time), by whom, and even what
transactions were performed. Some logs even show you
if the transaction was or was not successful with some
type of message.
IRQ values for a device may be set through
software or by manually setting them through the use of
jumpers or DIP switches on the expansion board for the
device. When configuring devices, it is important that
you do not have two devices that use the same IRQ.
NETWORK CONFIGURATION
Software Interrupt
Equipment, the connections, and equipment
settings for a network comprise the network
configuration. The equipment refers to the hardware
(computers, peripherals, boards, and cables), but may
also include software under certain circumstances.
Executing programs also use interrupts to get
resources needed to perform some action. There are
software interrupts to access a monitor screen or disk
drive, to handle a keystroke or a mouse click, and so on.
1-4
Some of these setting changes include:
There are software interrupts for handling specific
requests and for performing specific actions (for
example, determining memory size). Interrupts can
provide access to more functions (for example, DOS
interrupt 2AH provides for network control functions).
Adjusting memory partitions
Drive/directory access
Number of users
This is by no means a complete list of possible
changes that can be made; refer to the operator’s manual
for your specific software for changes that can be made.
SOFTWARE CONFIGURATIONS
All of the software that will be installed on the
network will be configured for use on the system.
Unfortunately, the manufacturers can’t configure the
software to function properly on each and every system.
It will be up to you to make configuration changes to get
the optimum performance from the specific software
that will be loaded on the network.
Modifying Parameters
The modification of the network parameters on
your specific system will depend on the software being
used. Each manufacturer sets up the software to run at
optimal performance. There will be times that the
network’s performance falls off because of adding
additional equipment, creating the need to change the
parameters. When the parameters must be changed,
always refer to the operator’s manual for the specifics.
These changes can include one or more of the
following:
Available memory
Type of peripheral (e.g., disk or tape drives,
printers, etc.)
A number of parameters can be changed to improve
the network’s performance, including increasing the
amount of memory used for disk sharing, print
spooling, and printing. By increasing the buffer used
for transferring files between the file server and
workstations, the file server does not have to perform as
many send operations and can perform other network
procedures more quickly. By increasing the size of the
buffer used for handling user requests, more user
requests can be processed and the network can perform
faster.
Number of users
Access speeds
Available disk space
Before making any changes to the software, ensure
that there are adequate backups available to restore the
system if problems are encountered. The most
important thing to remember, when making changes, is
to read the installation instructions that were supplied
by the manufacturer first.
NETWORK PORT CONFIGURATION
A port is a connection on the back of the computer
where you connect peripherals, switches, networks, or
other devices. The port provides the electrical and
physical interface between the device and the computer.
There are two types of ports:
NETWORK PARAMETERS
If you think about the network, its performance is
governed by both the hardware and software. The
hardware has certain limitations that are set by the
manufacturer and can’t be changed. You can’t speed up
disk or memory access times, no matter what you do.
The software, however, can be changed to help make
the network run better.
Parallel: A hardware connection used to send or
receive a lot of data over a short distance. These
ports typically send eight bits of data
simultaneously.
Serial: A hardware connection that is used to
send data one bit at a time and is very good for
sending information over a long distance.
Setting Parameters
Although the software is designed to run at the
optimal rate, because each system is different there are
some changes that can be made. Changes to these
settings can allow the system to run even better, using
all of its resources.
Port Address or Name
A port address is a bus or memory address that is
associated with a particular hardware port. The port
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Software Limits
will have at least enough storage allocated to handle the
data being written or read at the port.
No matter which software package, whether
application, mail, or operating system, there is a limited
number of users that can use the software at one time. It
is far cheaper to buy one multi-user package that allows
for 25 users than to purchase 25 individual copies. But,
it might run just a bit slower than an individual copy.
A port name can be used instead of an address to
refer to a port. A name is normally easier to remember
than an address. Operating systems sometimes have
predefine names associated with certain ports. For
example, DOS reserves COM1 and LPT1 to refer to the
first serial and parallel ports, respectively.
ANALYZE CONFIGURATION
NETWORK SOFTWARE
Analyzing the configuration of the network can be
accomplished in two different ways. The first and
simplest way happens when the computer is turned on;
the operating system goes out and checks the
configuration. The second way is accomplished by
using an application to test whether a remote device is
properly connected to the system. The use of an
application is the best way to analyze the configuration.
Networks require the interaction of software and
hardware. The system software to operate and control
the network must be specifically designed for network
operation. The application software/programs to solve
user problems must also be specially designed to run on
a network. Between the system software and the
application software/programs, two pieces of software
are needed. One is the telecommunications access
software. It provides application programs access to
the network so they can send and receive data. The
other is the teleprocessing monitor, which is the
interface between the telecommunications access
software and the application programs. It handles the
details of integrating these two. To install the system
software, as with any software, follow the installation
instructions supplied with the software.
The application tests the remote device by sending
out a signal to each device and waiting for the signal to
return. This process is called “pinging.” The ping sent
out is called an echo message, and the reply is called an
echo reply message. The application sends out the echo
message and, if the device is properly connected, it
sends back an echo reply message. The receipt of this
echo reply indicates that there is a viable connection.
Some version of application software reports on how
long it took to receive the echo reply and any lost
replies. These reports provide information about the
traffic and noise levels on the network.
SYSTEM SOFTWARE
It takes special system software to handle the
unique and dynamic workloads of a network. This
special software is called network system software.
The network system software is sometimes referred to
as the network operating system (NOS). It is different
from the type of system software you normally use on
your stand-alone PC. Network system software must be
able to handle multiple users, multiple peripherals,
network security, and be able to share information and
application software, just to name a few differences.
Normally, network system software runs on the network
server. It includes such things as the network’s
operating system software, communications software,
and all the programs needed to manage the sharing of
information and resources on the network. Without it,
there would be no way to coordinate and manage the
many components of a network into a functioning
whole.
SYSTEM RESOURCE LIMITS
The advantage of a network is it allows several
people to share resources, both hardware and software.
Hardware resources refer to printers, disk drives, CDrom drives, scanners, and modems. Software resources
include operating system, drivers, applications (word
processing, database, etc.), management software, and
data files. To avoid problems, such as slow response
time and unavailability of resources, you must know the
limits of the system resources.
Hardware Limits
The limitation involved with hardware is going to
be waiting. A particular piece of peripheral equipment
can be accessed by one user at a time. Only one job can
be printed at a time, and only one user can be using a
single modem at a time. This small inconvenience of
access outweighs the cost of several different pieces of
the same type (i.e., several printers or modems).
Network system software provides multitasking
capabilities. If the network is to serve multiple users at
the same time, then the server must be able to perform
tasks so fast they appear to be processed
1-6
identification numbers along with their passwords (as a
double check) to gain access to information. Another
reason why data must be made secure is to prevent
unintentional damage that can result when more than
one user accesses and changes the same information at
the same time. In a case such as this, neither user would
know what the other had done, and the result would be
corrupted data. To prevent this, network software often
provides you with some type of locking capability.
This locking feature prevents others from accessing the
file or record when you are working on it.
simultaneously. An example of multitasking is to have
the network server transfer a message (using a program
called E-mail) from one PC to another, save a 50-page
document to hard disk, and send a report to a printer, in
rapid succession. Only systems with multiple
processors, such as a system with two 386 or 486
microprocessors, can process information
simultaneously.
Network system software provides utility
programs, such as electronic mail (or e-mail). E-mail
gives network users the ability to send messages to one
another over the network. If for some reason you
needed to send a message to all the network users,
E-mail is capable of sending your message to multiple
users. Other utility programs sort, merge, and print
files.
To ensure a well-managed (network), the data must
not only be secure, it must also be backed upon a regular
basis. Files must be backed up if all the information on
the network server’s hard disk is to be saved in the event
of a hard disk failure, a sudden power surge, or loss of
power. Tape backup systems are very effective in that
not only the tapes but also the tape units themselves can
be stored off-site, which provides for additional
security.
Network system software also provides data
protection. This includes data security/integrity and
backing up of files. Data security is a must if you are to
limit access to sensitive and classified information.
Data integrity prevents files from being updated by
more than one user at a time. There are a number of
ways you can control access to information on the
network. One way is to divide the shared hard disk into
several different sections, similar to making logical
partitions. Once the different areas have been
established, you can specify how the user can access
them. Generally, the different levels of access can be
designated for either private, shared, or public use. They
are defined as follows:
APPLICATION SOFTWARE
In addition to network system software, users of
(network) require application software to carry out
their specific requirements. You are familiar with many
of the application software functions/packages
available. They include word processing programs,
database management programs, spreadsheet
programs, computer aided design (CAD) programs,
tutorials, and so on. Application software shared on a
network is different from the software you use on your
individual or stand-alone PC. It is specially designed to
work on a network—to handle the demands of many
users and to share resources while serving many users.
It can also provide data security features, such as file or
record locking and password recognition. Because
network versions of application software are designed
to be used by many users, a network software license
agreement often costs more than a standard license.
PRIVATE USE Only one user is allowed to
access and make changes to the data in this area.
For example, all of PO1 Smith’s work is located
in the area \SMITH. Only PO1 Smith has access
to this area, and only she can make changes.
SHARED USE All users are allowed to access
and make changes to the data in this area. For
example, a shared area called \ADMIN could
contain correspondence that can be updated by
all the command’s Yeomen.
Before leaving this section, you need to know a few
other things about network software. Network system
software features often vary from one network system
to another. The system software can also dictate what
hardware components CAN and CANNOT be used,
and how the network CAN or CANNOT be configured.
PUBLIC USE All users are allowed to access
this area; however, they cannot make any
changes to the data. For example, the area called
\DIRECTIV contains all command directives.
You would want your users to be able to view the
data but not be able to make any changes.
SOFTWARE INSTALLATION
Security and data protection are provided by
identification and password security. When the users
log on the system, they must enter their correct
Before installing software on an individual’s PC or
on the network server, you will need to know the
minimum system/hardware requirements for that
1-7
SOFTWARE TESTING
software. You will normally find this information on
the side of the box and sometimes even on the back of
the box the software comes in. The following
requirements and recommendations will normally be
listed:
Once the software is installed on the network, it
must be tested. The reason for the testing is to make sure
that all aspects of the program work. There are two
avenues for testing the software: an independent testing
company, and end-users.
The advantage of an independent testing company
is that it will use a more comprehensive and systematic
testing method. Testing aimed at the generic network
user is the disadvantage of the testing company.
Using end-users has both advantages and
disadvantages when it comes to testing the software. An
advantage is that the end-users will test all facets of the
software. A disadvantage is the haphazard methods of
most end-users when it comes to testing the software.
SYSTEM RESTORATION
The network is the most error-prone of the system
components. Usually, multiple vendors are involved,
and too few qualified personnel are available to support
all the implemented networks. Due to these inherent
problems with the network, system degradation is a part
of operation, and getting the system back into normal
operation is of great importance.
Three primary methods are used to provide service
restoration after system degradation. They are as
follows:
Any other system/hardware requirements that may
be needed will also be listed. As an example, these
requirements might include: one CD-ROM drive;
microphone, for voice annotation feature; a mouse or
compatible pointing device; 2400 or higher baud
modem (9600 baud modem recommended);
headphones or speakers; and type of messaging
software required to use e-mail; etc.
Redundancy. Redundancy refers to duplicate
hardware and network facility segments that are
available at all times. If the primary path fails, a
secondary path can continue network operation.
Rerouting. Rerouting is the transmission of
information along alternative paths. The end-to-end
transmission initially required is still obtained.
Once you have determined all of the above
information, you will need to determine whether it will
be run on a network as shared. Before you install the
software, you need to read the installation instructions
that come with the software application in their entirety.
It is strongly suggested that you read a file normally
called the “READ. ME” file, because that is where you
will find the most up-to-date information (changes) that
have been made to the application.
Reconfiguration. Reconfiguration is the
manual or automatic reconfiguration of equipment
and/or lines to achieve the original end-to-end
connections. Reconfiguration may be the most costly
method in time because it requires knowledgeable
personnel and the appropriate switching of equipment.
These three modes of operation are short-term
solutions meant to keep information moving. A better
solution is to correct the degraded or failed circuit
and/or equipment so normal operation is restored.
1-8
CALCULATING NETWORK
CAPACITY
NETWORK DESIGN
The first step in designing a network is to decide
whether or not a network is needed. This decision is
made easier by soliciting network requests from the
command. Once the decision is made to design and
install a network, you need to look at the capacity and
reliability of the network and the design options.
After you’ve determined the available resources,
use only a portion of these for your working
calculations. This downsizing will protect you against
the losses of these resources.
Many design options are available for designing
and building a LAN. Four interrelated factors
contribute to this great flexibility. They are physical
layout (topology), access method (protocol), physical
connection (cabling), and networking operating system
(NOS). There is one additional factor to be considered
when designing a network, the need for security. This
need for security is met by the implementation of a
firewall.
The amount by which you should decrease your
estimates depends on the possible costs if your network
is a failure and on how stable the resources are. A
general rule to follow is to assume that your available
resources will be anywhere from 10 to 50 percent less
than estimated. Let’s say, that you have 25 PC
workstations available to connect to the network. You
should plan on connecting 22 (12% less than available),
which would leave you with 3 spare workstations.
Another example would be: if your NOS is capable of
having 250 accounts, reducing this quanity by 10% (25)
will help reduce the time that the users will be waiting
for the network to respond to their request.
NETWORK REQUESTS
Before committing the money to install a network,
you need to research the need for a network for the
command. The best way to conduct this research is by
using a network request. Always make sure you have
all the available information to guide your planning.
The following are some guidelines to use when
beginning to plan for a network:
The opposite of this rule is applied when it comes to
the cost calculations. When you decide how much time
and money it is going to cost, it is a good idea to add an
amount or a percentage to the calculations. Projects like
networks never seem to be completed on time or at cost,
due to unforeseen circumstances.
Calculate your needs as completely as possible.
This will help you decide what components and
services will need to be included in the network.
LAN CONFIGURATIONS (TOPOLOGIES)
Determine what resources are available at your
command for planning, implementing, and
running a network.
The physical arrangement of a LAN’s components
is called its configuration or topology. The three major
types of LAN configurations, or topologies, are the
star, the bus, and the ring. You can also create hybrid
topologies by combining features of these
configurations. For example, several bus networks can
be joined together to form a ring of buses.
Determine who needs access to the network and
where these people are located. This
information will help determine whether a
network is a necessary or feasible solution for the
command’s needs. It will also provide
information regarding cabling requirements.
Each topology requires LAN components to be
connected in a different arrangement. These
components are also referred to as nodes. Remember, a
node is any point on a network where data can be sent
(transmitted) or received—a workstation, server, and so
on.
Get to know the current usage and needs in
detail. This information will also help decide
whether a network is the best solution.
Get a detailed drawing of office locations,
existing wiring, and possible server locations.
The Star Network
After gathering and evaluating the information, the
decision can be made as to whether or not a network is
the way to go. If it is decided to go with a network, it is
time to determine what resources are available.
In a star network, each component is connected
directly to the central computer or network server, as
1-9
shown in figure 1-2. Only one cable is required from the
central computer to each PC’s network interface card to
tie that workstation to the LAN. The star is one of the
earliest types of network topologies. It uses the same
approach to sending and receiving messages as our
phone system. Just as a telephone call from one person
to another is handled by a central switching station, all
messages must go through the central computer or
network server that controls the flow of data. You can
easily add new workstations to the network without
interrupting other nodes. This is one of the advantages
of the star topology.
Another advantage of star topology is that the
network administrator can give selected nodes a higher
priority status than others. The central computer looks
for signals from these higher priority workstations
before recognizing other nodes. Also, the star topology
permits centralized diagnostics (troubleshooting) of all
functions. It can do this because all messages must first
go through the central computer. This can prove
invaluable for ensuring network security has not been
breached. So much for the good news; now for the bad
news, or the disadvantages of the star network. Of all
the topologies, the star is the least reliable because it has
a single point of failure. The network relies mainly on
the central computer for all functions. If it fails, all
nodes also stop functioning, resulting in failure of the
entire network. This is precisely the same weakness
multi-user computer systems have that rely on a central
processor.
and the far ends of this cable never meet (see figure 1-3).
Bus LANs are best suited to applications involving
relatively low usage of the bus coupled with the need to
pass relatively short messages from one node to another.
In many such networks, the workstations check whether
a message is coming down the highway before sending
their messages. Since all nodes share the bus, all
messages must pass through the other workstations on
the way to their destinations. Each node checks the
address attached to the message to see if it matches its
own address. Bus topologies allow individual nodes to
be out of service or to be moved to new locations
without disrupting service to the remaining nodes.
Unlike the star topology, where dozens of cables
come together at the central computer causing logistical
problems, bus cabling is simple. The bus topology is
very reliable, because if any node on the bus network
fails, the bus itself is NOT affected, and the remaining
nodes can continue to operate without interruption.
Many of the low-cost LANs use a bus topology and
twisted-pair wire cabling.
A disadvantage of the bus topology is that generally
there must be a minimum distance between
workstations to avoid signal interference. Another
disadvantage is that nodes must contend with each other
for the use of the bus. Simultaneous transmissions by
more than one node are NOT permitted. This problem,
however, can be solved by using one of several types of
systems designed to control access to the bus. They are
collision detection, collision avoidance, and token
passing, which we will discuss shortly. Also, there is no
easy way for the network administrator to run
diagnostics on the entire network. Finally, the bus
network can be easily compromised by an unauthorized
network user, since all messages are sent along a
common data highway. For this reason, it is difficult to
maintain network security.
The Bus Network
The bus topology is like a data highway. That is, all
components or nodes are connected to the same cable,
Figure 1-2.—A star network topology.
Figure 1-3.—A bus network topology.
1-10
workstation by bypassing it and still be able to maintain
the network’s integrity. One of the major issues in a ring
topology is the need for ensuring all workstations have
equal access to the network.
One of the major disadvantages of ring topologies is
the extreme difficulty of adding new workstations while
the network is in operation. Normally, the entire
network has to be brought down while a new node is
added and cabling reattached. However, this particular
problem can be overcome by initially setting up the
network with additional connectors. These connectors
enable you to add or remove nodes while the network
remains intact and in operation. The addition of the
connectors is accomplished with the addition of a
multistation access unit (MAU). The MAU is a wiring
concentrator which allows workstations to be either
inserted or bypassed on the ring.
Figure 1-4.—A ring network topology.
The Ring Network
In a ring network, all of the components or nodes
are connected to the main cable, and the cable forms a
ring, as shown in figure 1-4. This topology allows a
node to send a message to another node on the ring.
However, the message must be transmitted through
each node until it reaches its destination. Messages
proceed from node to node in one direction only.
Should anode fail on the network, data can no longer be
passed around the ring unless the failed node is either
physically or electronically bypassed. Using bypass
software, the network can withstand the failure of a
The Distributed Star (Tree) Network
The distributed star or tree topology (figure 1 -5) can
provide many of the advantages of the bus and the star
topologies. It connects workstations to a central point,
called a hub. This hub can support several workstations
or hubs which, in turn, can support other workstations.
Distributed star topologies can be easily adapted to the
physical arrangement of the facility site. If the site has a
high concentration of workstations in a given area, the
system can be configured to more closely resemble a
Figure 1-5.—A distributed star (tree) network topology.
1-11
and protocol. The principal access methods are
contention and token passing.
star topology. If the workstations are widely dispersed,
the system can use inexpensive hubs with long runs of
shared cable between hubs, similar to the bus topology.
Contention
PROTOCOLS
The contention method features Carrier Sense
Multiple Access (CSMA) and Carrier Sense Multiple
Access with Collision Detection (CSMA/CD). (See
figure 1-6.) Access for both is on “a first-come, firstserved basis. The CSMA scheme is very similar to a
citizens band (CB) radio. Stations with data to send
listen to the channel and wait until it is clear to transmit.
With CSMA/CD, if two or more workstations transmit
simultaneously, their messages will collide. As soon as
a workstation detects a collision, it ceases transmission,
monitors the network until it hears no other traffic, and
then retransmits. Most contention networks assign a
unique retry algorithm to vary the wait-and-retry
period. This algorithm reduces the likelihood that after
a collision, two workstations will transmit retries
simultaneously.
Network protocols are an important component;
they define how networks establish communications
between elements, exchange information, and
terminate communications. Protocols have two major
operational functions. They establish the circuit for
transmission (handshaking) and for the transmission
itself. Transmission is conducted subject to the line
dicipline. The line discipline is the sequence of
operations that actually transmits and receives the data,
handles the error-control procedures, handles the
sequencing of message blocks, and provides for
validation for information received correctly.
Two representative protocols, which control line
dicipline, are: the Binary Synchronous
Communications Protocol (Bisync) and the
Synchronous Data Link Control (SDLC).
Bisync is a half-duplex protocol that transmits
strings of characters at lower speeds over dial-up
circuits. Information movement is one direction at a
time, with each data transfer being answered by an
acknowledgement.
SDLC is a control procedure that sends multiple
blocks of data and returns a single acknowledgement
for many blocks, thereby increasing the amount of time
spent transmitting data. The bits that are put before and
after the message at the transmitting end are removed at
the receiving end, so only the message is presented to
the user.
The hardware chosen for the network plays apart in
the choice of network protocol. Most users and many of
the vendors that build clone-type equipment would like
to see universal interfaces. Others feel that the
availability of different specifications will lead to a
proprietary set of equipment, even though they favor the
overall IS0 specifications (which are covered later in
this chapter).
ACCESS METHODS
Another decision to be made is which access
method to use. Access methods are the arrangements
used to ensure that each workstation has fair and equal
access to the network. The access method that will be
used is governed primarily by the network’s topology
Figure 1-6.—A bus network using the CSMA/CD access
method.
1-12
Token Passing
printer is used by all nodes, how one file is passed
among many users, and so on. If order and discipline
are to be maintained on the network, standards or
protocols must be established and adhered to. This
allows the LAN to function in an efficient and effective
manner.
Token passing is an orderly access method (figure
1-7). Each workstation passes on the opportunity to
transmit to its closest neighbor, until a station is found
with a message to send. This permission to transmit is
called a token. When a workstation with data to send is
handed a token, part of the token is changed, indicating
it is carrying a message, and then data is transmitted
with the token. The token is then passed around the
network, and every station checks to see if the message
is intended for them. The receiving station copies the
message from the token but then passes the unchanged
token along the network. When the transmitting station
receives the same token, it knows the message has been
passed around the network. The transmitting station
erases the message and puts the empty token back into
circulation on the network. The amount of information
that may be transmitted during possession of the token
is limited so that all workstations can share the cable
equally.
Over the past few years, a number of network
standards or protocols have been developed by the
International Standards Organization (ISO). They
provide some level of uniformity among computer
manufacturers and network vendors. ISO is one of
several governing organizations in this field that has
developed a series of protocols (rules to live by) to
ensure compatibility for the many different vendors
who design network hardware and software products.
IS0 has defined a seven-layer architecture. These seven
layers of standards, shown in figure 1-8, define a
generalized architecture called the Reference Model of
open Systems Interconnection. It is also known as
the OSI reference model or OSI model. The primary
purpose of the OSI model is to provide a basis for
coordinating the development of standards that relate to
the flexible interconnection of incompatible systems
using data communications facilities.
Network Standards
These access methods (CSMA/CD, CSMA/CA,
and token passing) with their transmission medium
(twisted-pair wire, coaxial cable, or fiber optic cable),
are just one of several aspects (or levels) of an entire
LAN structure. The topologies and network access
methods just presented only establish a way to connect
workstations or nodes together and how to pass along
packets of data. These packets of data may be
programs, data, system or personal messages, and so on.
Above this hardware/software level are a number of
other levels that are just as important in a LAN’s design.
These are the levels that define how the LAN system
manages its resources, how a user like yourself is able to
log onto another node’s hard disk, how a common laser
The OSI model does NOT define any one vendor’s
particular network software as such, nor does it define
detailed standards for any given software. It simply
defines the broad categories of functions that each of the
seven layers should perform. The OSI model can
include different sets of standards at each layer that are
appropriate for given situations. For example, in a very
simple data communications system, one that uses a
simple point-to-point link, the software at the higher-
Figure 1-8.—The OSI model showing the seven software
layers.
Figure 1-7.—A ring network using the token passing access
method.
1-13
level layers (say 5, 6, and 7) might be very simple or
possibly nonexistent. However, in a very complex data
communications system, all seven software layers may
be implemented. Although there is no requirement for
any hardware or software vendor to adhere to the
principles set forth in the OSI model, there is a
worldwide trend in the computer industry toward
acceptance and conformance to these standards.
Voltages and pulse encoding of bits
Media and media interface (cables, connectors,
NIC, and so on)
Line discipline (full- or half-duplex)
Pin assignments
In our mail analogy, the mail truck and the highway
provide the services of the physical layer.
About now, you may be asking yourself, what are
these seven software layers (shown in figure 1-8), and
why all the need for protocols? Don’t all computers
work in binary? Do they not all have operating
systems? If a computer wants to communicate with
another system, do you not simply connect them
together using some type of cable? The answers to these
questions are yes, yes, and yes; however, the
commonalities seem to stop there.
Layer 2—The data link layer provides error-free
transmission of information over the physical medium.
This allows the next higher layer to assume virtually
error-free transmission over the link. The data link layer
is responsible for getting data packaged and onto the
network cable. It manages the flow of the data bit
stream into and out of each network node, as follows:
Creates and recognizes frame boundaries
Ideally, if the hardware, network software,
application software, and cabling were all supplied by
the same manufacturer, we would have relatively few
problems to contend with when we design and
implement a network. Everything would work together
rather smoothly. However, a computer manufacturer’s
architecture can make it difficult to interconnect
hardware offered by other competing
manufacturers/vendors. The protocols used by
communications devices are also highly complex and
are often completely different from one manufacturer to
another. Then, there is the network software. Network
software from one LAN vendor usually won’t work on a
competitor’s network, nor will the application
programs. Even the cabling must be selected for a
specific local-area network.
Checks received messages for integrity
Manages channel access and flow control
Ensures correct sequence of transmitted data
The data link layer detects, and when possible,
corrects errors that occur in the physical layer without
using the functions of the upper layers. It also provides
flow-control techniques to ensure link-buffer capacity
is not exceeded. In our analogy, the data link layer is
concerned with sending the mail trucks onto the
highway and making sure they arrive safely.
Layer 3—The network layer decides which
physical pathway the data should take, based on
network conditions, priorities of service, and other
factors. Software on the network interface card must
build the data packet so the network layer can recognize
and route the data to the correct destination address. It
relieves the upper layers of the need to know anything
about the data transmission and switching technologies
used to connect the systems. It is responsible for
establishing, maintaining, and terminating connections
across the intervening communications facility, as
follows:
We could go on and on explaining the many
incompatibilities that exist within these different areas,
but the good news is that many hardware and software
manufacturers/vendors provide interfaces. These
various types of interfaces (bridges, gateways, routers,
and so on) allow networks to be compatible with one
another. At this point, we briefly talk about the seven
software layers defined in the OSI model to give you
some idea of what they are and why they are needed. To
illustrate how the OSI model works, we are using the
analogy of sending a letter using the U.S. postal system.
Addresses messages
Sets up the path between communicating nodes
on possibly different networks
Layer l—The physical layer is concerned with
the transmission of the unstructured raw bit stream over
a physical meduim. It addresses the electrical,
mechanical, and functional interface to the carrier. It is
the physical layer that carries the signals for all the
higher layers, as follows:
Routes messages among networks
Is concerned with the sequence delivery of data
packets
1-14
Performs synchronization between end-user
tasks by placing checkpoints in the data stream
so if the network fails, only the data after the last
checkpoint has to be retransmitted
Controls congestion if too many packets are on
the network
Translates logical addresses or names into
physical addresses
Provides dialogue control (who speaks, when,
how long, and so on)
Has accounting functions to count packets orbits
sent by users to produce billing information
The session layer in our postal agency recognizes
different zip codes and reroutes letters.
This layer acts in our postal service analogy, like the
regional mail distribution centers throughout the
country. The trucks are directed to the centers and are
routed along the best path to their final destinations.
Layer 6—The presentation layer formats data to
be presented to the application layer. It can be viewed as
the translator for the network. This layer provides a
common representation for data that can be used
between the application processes. The presentation
layer relieves the applications from being concerned
with data representation, providing syntax
independence, as follows:
Layer 4—The transport layer ensures data units
are delivered error-free, in sequence, with no losses or
duplications. It relieves higher layer protocols from any
concern with the transportation of data between them,
as follows:
Message segmentation—accepts data from the
session layer, splits it up into smaller units, and
passes the units down to the network layer
Encodes data in a standard way (integers,
floating point, ASCII, and so on)
Provides data compression to reduce the number
of bits that have to be transmitted
Establishes and deletes host-to-host connections
across the network
Provides data encryption for privacy and
authentication
Multiplexes several message streams onto one
channel and keeps track of which message
belongs to which connection
This layer functions like a translator who translates a
letter from French into English.
Layer 7—The application layer serves as the
window for the application process to access the OSI
environment. This layer represents the services that
directly support users and application tasks. It contains
a variety of commonly needed protocols for the
following:
Provides reliable end-to-end delivery with
acknowledgment
Provides end-to-end flow control and window
management
The transport layer functions are provided by the mail
truck dispatcher, who takes over if there is a wreck out
in the system. If the network goes down, the transport
layer software will look for alternate routes or perhaps
save the transmitted data until the network connection is
reestablished.
Network virtual terminals
File transfers
Remote file access
Electronic mail
Layer 5—The session layer allows users on
different machines to establish sessions between them.
It performs the functions that enable two applications to
communicate across the network, performing security,
name recognition, logging, administration, and other
similar functions. Unlike the network layer, this layer is
dealing with the programs in each machine to establish
conversations between them, as follows:
In our analogy, the application layer is the person who
writes or reads the letter.
Allows two applications processes on different
machines to establish, use, and terminate a
connection (or session)
A data communications network must have cabling
to allow individual computers and other peripherals to
talk to one another and share resources. And wouldn’t it
be easier if there were only one type available? There
Network management
CABLING
1-15
would be fewer hassles when it came time to figure out
such things as line speeds, line capacities, variations in
line distortion, and so on. However, there area number
of types, ranging in cost and capabilities. In the
following paragraphs, we examine the advantages and
disadvantages of twisted-wire pairs, baseband and
broadband coaxial cabling, and fiber optic cabling.
crosstalk exists in twisted-wire pairs whenever
transmission occurs at a high rate of speed. Crosstalk is
taking place whenever you can hear someone else’s
conversation in the background; say Mr. Frost telling
Mrs. Christmas what a great recipe he has for southern
fried chicken, or Mrs. Brush telling Mr. Smith what a
large fish she caught in the Gulf of Mexico, while you’re
trying to carry on a conversation with your party. With
voice communications this really isn’t a problem;
however, crosstalk can inhibit the high-speed
transmission required for data communications.
Twisted-wire Pairs
Twisted-wire pairs, also known as twisted-pair wire
or cable, is by far the least expensive transmission
media. It consists of two insulated wires twisted around
each other so that each wire faces the same amount of
interference (noise) from the environment (see fig. 1-9).
Unfortunately, this noise becomes part of the signal
being transmitted. Twisting the wires together reduces
but does not eliminate the noise.
Twisted-wire pairs used in data communications
are either private or public lines. Private lines are those
provided by the user. Public lines are those provided by
a common carrier such as American Telephone and
Telegraph (AT&T). Generally, public lines are used
whenever distances are great or the terrain or other
environmental factors prohibit the use of private lines.
Public lines may be either switched lines or leased lines.
Twisted-pair wire comes in a wide range of gauges
and pairs. Wire has an American Wire Gauge (AWG)
number based on its diameter. For network purposes,
22- and 24-gauge wires are the two most common types
of twisted-pair media. Some local-area networks use
the same inexpensive, unshielded twisted-pair cables
telephone companies use. Others require a higher data
grade quality. It’s not uncommon to have several
hundred pairs (and, in some cases, thousands) of wires
placed in a single cable. Normally, each twisted-wire
pair in a cable can accommodate a single phone call
between two people or between hardware devices.
Switched lines are used whenever the amount of
data to be transmitted is short in duration or when many
locations must be contacted for relatively short periods
of time. There is a drawback. The telephone company
cannot guarantee you exactly which path or switching
equipment such a connection will use. Therefore, the
speed and quality of the switched connection are
questionable.
Leased lines come into play when the connection
time between locations A and B is long enough to cover
the cost of leasing, or if higher speeds than those
available with switched lines must be attained. Leased
lines can also be conditioned by the telephone company
to lower the error rate and increase transmission speeds.
Conditioned leased lines typically operate at speeds of
up to 64,000 bits per second (bps). Very-high-speed
connections are also available from the common carrier.
These are designated T1, T2, T3, and T4, and offer
transmission rates of 1.5, 6.3, 46, and 281 million bits
per second (Mbps), respectively.
The advantages of using telephone wires are their
relative low cost and their availability. Their
disadvantages include susceptibility to signal distortion
errors and the relatively low transmission rates they
provide over long distances. Twisted wire can handle a
data flow of up to approximately one megabit per
second (Mbps) over several hundred feet. For a small
local-area network with a limited number of users,
twisted-pair is an ideal choice because it is both
inexpensive and easy to install. A phenomenon called
Coaxial Cables
Coaxial (or coax) cable, the medium used by most
cable television companies, was developed primarily
because of the crosstalk in twisted-wire pairs when
transmission occurs at a high rate of speed. While coax
is more expensive than twisted-pair, it can transmit data
significantly faster, over much longer distances, and
with less electrical interference.
Coaxial cable is made up of one or two central data
transmission wires composed of copper surrounded by
Figure 1-9.—Twisted-wire pairs (2 wire pairs shown).
1-16
an insulating layer, a shielding layer, and a weather
proof outer jacket, as shown in figure 1-10. It is almost
as easy to install as twisted-pair, and is the preferred
medium for many of the major local-area networks.
Coaxial cable is used extensively in local-area networks
whenever the distance involved is relatively short,
generally less than 2 miles for baseband LANs and 10
miles for broadband LANs. It is used in both baseband
and broadband networks. Wait a minute! You say you
want to know what the terms baseband and broadband
mean and how they relate to networks? Not to worry;
we explain them to you a little later in the text, but for
now, all you need to know is that they both deal with the
way data is transmitted (in the form of electrical signals)
through some type of medium.
Figure 1-11.—Fiber optic cable.
Monomode— Single fiber cable
Multimode— Several fibers within a cable
Graded index— A variation of multimode
Fiber Optic Cable
Some of the major advantages of fiber optics over
wire media include speed, size, weight, longevity, and
resistance to tapping without being noticed. Since it
carries no electrical current, it is immune to electrical
interference of any kind, and there is no worry of it
being a shock hazard.
Fiber optic cable is to coaxial cable is to twistedpair as the F-18 Hornet is to the Corvette is to the model
T. It is the newest of the communication mediums, one
that was spurred by the development of laser
technology. Fiber optic cable (shown in fig. 1-11)
consists of thousands of clear glass fiber strands, each
approximately the thickness of a human hair.
Transmission is made possible by the transformation of
digital data into modulated light beams, which are sent
through the cable by a laser light-emitting diode (LED)
type device at incredibly fast speeds. Transmission
rates available (as of 1990) range up to approximately 1
billion (or giga) bits per second (Gbps), with speeds
over 2 Gbps possible. When thinking in terms of
frequencies, light frequencies are extremely high. They
are approximately 600,000 times that of the highest
television channel. In terms of data communications,
the higher the frequency of the signal, the more
information it can carry. Put simply, every hairlike fiber
within a fiberoptic cable has the capacity to carry many
hundreds of local-area network channels
simultaneously. When dealing with fiber optic cable,
you will hear such terms as:
One big disadvantage of fiber optic is the tighter
restrictions on how much the cable can be bent. Other
disadvantages include higher cost, and the inability to
add on new workstations while other stations are active.
Although it is relatively easy to splice the fiber optic
cable and add new stations, the network or a portion of
the network must be down while preparing the splice.
On the other hand, if your activity has serious
interference problems, or has a need for absolute
network security, or the need to send signals several
miles, then fiber optics might be the only solution.
Cable Selection
About now, you may be asking yourself, why all the
fuss over transmission speeds? Why not just simply
choose the cheapest transmission medium available and
use it? It may not be the ideal situation, but it would get
the job done, right? This is true; and with that in mind,
we ask you this question. Would you put regular
unleaded gasoline in your brand new car that happens to
have a high-performance engine? The engine may not
run as well as you would like, but it would get the job
done, right? The same is true of transmission speeds and
the different levels of speed within a computer system.
To put it another way, the speed of transmission is very
much related to the type of transmission medium used
between stations in a network.
Figure 1-10.—Coaxial cable,
1-17
Most computer processing units (CPUs) are able to
execute instructions and basic decision-making steps at
a rate of several million instructions per second. Data
can be transferred between the computer’s memory and
the cpu at these same rates of speed. The ideal network
could keep up with the high speed of the cpu and be able
to transfer data between the stations of the network at
rates close to the rates that data is moved around within
the cpu and memory. However, this is just not possible
with a telephone line linked system, which is limited in
the range of frequencies it can carry. When highfrequency signals are carried by wire such as twistedpair, all sorts of electrical effects come into play. It’s not
sufficient to simply link computer systems with
common wire. Considerable thought must be given to
the electrical characteristics of the connection. The
cable selection must be made during the design phase of
the network to ensure that the decision is not left to be
made during the installation of the network.
UNIX®
Windows NT®
Novell® DOS 7
In most of these cases, the operating system’s
networking capabilities can be greatly enhanced
through the use of utilities or other third-party
programs. To learn more about these utilities or
programs, check the manuals that come with the
operating system.
FIREWALLS
Firewalls can be used for securing a local area
network from a public network like the Internet.
Firewalls are always a part of a much larger security
plan. Choosing a firewall starts with a clear definition
of the security goals. This includes decisions on what
logging and alarms are needed, what authentication is
acceptable and where security barriers are needed.
Once the policy, philosophy, and service goals are
defined, often only a few products on the market really
fit these needs.
NETWORK OPERATING
SYSTEM
A network operating system (NOS) is a software
package that makes it possible to implement and control
a network and enables users to use the resources and
services on that network. A NOS’s tasks include:
There are several types of firewalls that can be
divided into packet filtering and application layer
firewalls.
Providing access to files and resources;
Packet Filters
Providing electronic mail (e-mail) services;
Packet filters operate at a lower level than
application layer firewalls. Packet filters decide
whether to forward an IP packet based on the source or
destination address found at the network layer. Routers
typically implement this type of filtering, but since
packets containing bogus IP addresses can easily be
created, it’s not too hard to gain access through even the
most elaborate set of IP address filters. Although the
router on an Internet link can filter packets, it probably
wasn’t designed to provide the level of control that a
firewall product can. A router examines one packet at a
time and forwards the packet.
Enabling nodes on the network to communicate
with each other;
Enabling processes on the network to
communicate with each other;
Responding to requests from applications and
users on the network; and
Mapping requests and paths to the appropriate
places on the network.
A NOS may be server-based or peer-based. Server
based NOSs are considerably more complex and
powerful than NOSs for peer-to-peer networks. In a
server-based network, the NOS and the server run the
show, and the workstations will generally run a network
shell. By contrast, in a peer-to-peer network any station
can function as file server or as a client for network
services.
Application Layer Firewall
Application layer firewalls, on the other hand, are
designed specifically to control unwarranted access to
your network. They can also deal with some of the
trickier protocols. Application layer firewalls gain
more insight into the data conversations that traverse an
Internet link because they examine packets and
protocols at and above the transport layer, which
Operating systems which have built-in networking
capabilities include the following:
1-18
controls the dialogue between communicating end
nodes.
Employ filtering techniques to permit or deny
services to specified host systems as needed.
As an application gateway, the firewall typically
behaves as a client on the Internet and appears as a
server to users on its secure, protected side. When
operating in this mode, the firewall will examine
specific application protocols to decide whether
connections are permissible. The range of supported
application protocols varies from firewall to firewall,
but most examine such popular ones as TELNET, the
World Wide Web’s HyperText Transfer Protocol
(HTTP) or File Transfer Protocol (FTP).
Use an IP filtering language that is flexible, userfriendly to program, and able to filter on as many
attributes as possible, including source and
destination IP address, protocol type, source and
destination TCP/UDP port, and inbound and
outbound interface.
Use proxy services for services such as FTP and
TELNET, so that advanced authentication
measures can be employed and centralized at the
firewall.
Application layer firewalls offer greater protection
against hacker attacks than the packet filtering
firewalls. Besides providing stronger logging
capabilities, many firewalls can also provide features
like network address translation, authentication, and
virtual private net works.
The firewall should contain the ability to
concentrate and filter dial-in access. The firewall
should contain mechanisms for logging traffic and
suspicious activity, as well as mechanisms for log
reduction so that logs are readable and understandable.
If the firewall requires an operating system such as
UNIX®, a secured version of the operating system
should be part of the firewall, with other security tools
as necessary to ensure firewall host integrity. The
operating system should have all patches installed. The
firewall should be developed in such a manner that its
strength and correctness are verifiable. It should be
simple in design so that it can be understood and
maintained. The firewall and any corresponding
operating system should be updated with patches and
other bug fixes in a timely manner.
Choosing A Firewall
Once the decision is made to use firewall
technology to implement an organization’s security
policy, the next step is to procure a firewall that provides
the appropriate level of protection and is cost-effective.
We cannot say what exact features a firewall should
have to provide effective implementation of your
policies, but we can suggest that, in general, a firewall
should be able to do the following:
Support a “deny all services except those
specifically permitted” design policy, even if
that is not the policy used.
SUMMARY
Support your security policy, not impose one.
In this chapter, we have covered some of the areas
that need to be considered in the administration of a
network. We have discussed network operations, the
configuration of the network, network software, and
network design. This is by no means all that will be
required for administration, but it is a beginning.
Accommodate new services and needs if the
security policy of the organization changes.
Contain advanced authentication measures or
contain the hooks for installing advanced
authentication measures.
1-19
CHAPTER 2
LAN HARDWARE
Upon completing this chapter, you should be able to do the following:
Explain how to install, inspect, and test network components.
Describe how to make physical connections to networks.
Explain the function of a network server.
As noted in chapter 1, if the hardware, network
software, application software, and cabling were all
supplied by the same manufacturer, we would have
relatively few problems to contend with when we
design and implement a network. The answers to many
hardware and software incompatibilities are found in
the use of interfaces. These various types of interfaces
(bridges, gateways, routers, and so on) allow networks
to be compatible with one another.
Repeaters
Repeaters are used to amplify electrical signals
carried by the network. They work at layer 1 of the OSI
model—the physical layer. (The OSI model was
covered in chapter 1.) The function of a repeater is to
receive incoming signals (a packet of data), regenerate
the signals to their original strength, and retransmit
them. Repeaters are used to lengthen individual
network segments to form a larger extended network.
That is, repeaters allow a network to be constructed that
exceeds the size limit of a single physical segment by
allowing additional lengths of cable to be connected
(see figure 2-l). There is a catch, however. For a
repeater to be used, both network segments must be
identical-same network protocols for all layers, same
media access control method, and the same physical
transmission technique. This means we could connect
two segments that use the CSMA/CD access methods,
or connect two segments that are running under the
NETWORK COMPONENTS
More and more, LANs are becoming part of larger
networks. By connecting LANs together, any
peripheral device, such as external hard disk, printer, or
plotter can be shared by all users of the networks. This
makes more efficient use of expensive peripherals.
Repeaters can be used to amplify electrical signals;
which, in turn, allows transmissions to travel greater
distances. Bridges (also known as bridge servers) make
it possible to interconnect like LANs; that is, two
similar networks. Routers enable networks to
communicate using the most efficient path. Brouters
combine the functions of a bridge and a router.
Gateways (also known as gateway servers) make it
possible to interconnect unlike LANs; that is, two
dissimilar networks.
INSTALL COMPONENTS
The installation of network components is
dependent on the particular type of component, the
manufacturer, and the type of cable being used. When it
comes to installing one of these components, read the
instructions that are supplied with the component to
make sure that you install it properly.
Figure 2-1.—Repeaters used to lengthen individual network
segments.
2-1
token-passing access method. However, we cannot
connect a CSMA/CD segment to a token-passing
segment.
route to LAN C that would be shortest route, as
shown in figure 2-2, frame B.
Bridges
A brouter can work in either the second and third
layers of the OSI model—the data link layer or the
network layer. A brouter is a combination of a bridge
and router combined. If it can’t route a packet, it acts as a
bridge. Brouters are particularly useful if you have two
or more different networks. Working as a bridge, a
brouter is protocol independent and can be used to filter
local are a network traffic. Working as a router, a
brouter is capable of routing packets across networks.
Brouters
Bridges handle the first two layers of the OSI
model—the physical layer and the data link layer. Like
repeaters, bridges connect physically-isolated networks
to forma single logical network; however, a bridge has a
little more intelligence and can provide some
translation between dissimilar protocols. For example,
our token-passing segment wants to communicate with
our CSMA/CD segment. The bridge will “repackage”
the message from the token-passing segment into a
format that the CSMA/CD segment will understand.
Then, the bridge will act as a workstation on the
CSMA/CD segment and contend for access. The same
thing happens in reverse. A message is sent from the
CSMA/CD segment to the token-passing segment. The
bridge then “repackages” the message into a format the
token-passing segment is expecting and waits for the
token, just like any other workstation. An important
point to remember is that a bridge will pass on any
message it receives. Because the bridge is not smart
enough to know that unlike LANs do not understand
each other, it will go ahead and send the message.
Because the two LANs speak a different “language,”
the message will be ignored.
Gateways
Gateways work at OSI model layer 7—the
application layer. A gateway functions to reconcile
differences between two dissimilar networks.
Messages are not only repackaged for transmission
between different networks (CSMA/CD to tokenpassing), but the contents of the messages are converted
into a format the destination can use and understand.
Now our unlike LANs can talk to each other. Gateways
can also provide links between microcomputer
networks and mainframes.
A gateway is generally a dedicated computer with
an interface card and at least some type of software for
both of the environments being connected. The
gateway then runs special software that provides the
necessary conversion and translation services which, in
turn, allow the two environments to communicate.
Routers
Routers only connect networks running similar
access methods. They work at the third layer of the OSI
model—the network layer. Like bridges and repeaters,
routers can connect networks over different wiring
media and topologies. However, unlike bridges, routers
can intelligently determine the most efficient path to
any destination, based on predetermined delimiters.
Routers are often a better choice for interconnecting
remote installations and congested networks requiring a
single protocol. Let’s look at this more closely.
Let’s say we have a LAN made up of three tokenpassing segments, and each segment is connected via a
bridge. For a message to go from LAN A to LAN C, it
would have to travel through LAN A and LAN B before
it reaches its final destination, which is LAN C. See
figure 2-2, frame A. On a LAN that has large amounts
of message traffic, we can see how a bridge may slow
down the system. On the other hand, if the segments are
separated by routers, the router on LAN A would look at
the destination of the message and determine the direct
Figure 2-2.—Interconnecting LANS using (A) bridges and (B)
routers.
2-2
Concentrators
MODEMS AT WORK.— Put simply, the object of
a modem is to change the characteristics of a simple sine
wave, referred to as a carrier signal. We know this
carrier signal has several properties that can be altered
to represent data. It has amplitude (height); it has
frequency (a unit of time); and it has phase (a relative
starting point). Modems are capable of altering one or
more of these characteristics to represent data.
The main function of a concentrator is to serve as a
termination point for cable running from individual
nodes in a network. The cable connects to the network
or to another wire center.
A concentrator may have multiple boards or boxes
mounted on a rack. Each board is essentially a hub, a
wiring center for a single network’s nodes. Such boards
generally include light-emitting diodes (LEDs) to
indicate the status of each port on the board.
The job a modem performs can be divided into two
discrete parts or phases at each end of the
communications link. At the sending end, it converts
digital bit streams (strings of 0’s and 1’s) into analog sine
waves. This is the encoding process. Another
component within the modem then changes
(modulates) the analog signal so the data may be
transmitted simultaneously with other data and voice
traffic that has also been modulated. This process is
basically reversed at the receiving end. There, the
analog signal is brought back to its basic level
(demodulated), and the analog sine waves are
reconverted (decoded) back into their corresponding bit
streams (see figure 2-3).
Hubs
A hub is a box with a number of connectors to which
multiple nodes (PCs) are attached. It serves as a
common termination point that can relay signals along
the appropriate paths. All hubs provide connectivity,
and some even provide management capabilities. A hub
usually connects nodes that have a common
architecture. Although the boundary between
concentrators and hubs is not always clear, hubs are
generally simpler and cheaper than concentrators.
CODECs.— In today’s digital communications
lines, voice traffic is considered the outsider that digital
data used to be to analog lines. Voice can enter the data
communications lines only after being encoded into
digital form. It then must be decoded to be audible again
at the receiving end. The device used to perform the
encoding and decoding functions is known as a codec.
This is simply another black box conversion device that
has always been in existence in a slightly different form
as part of a modem.
Modems
In module 2, we introduced you to modems and
how they are used in a data communications
environment. They translate data from digital to analog
form at the sending end of the communications path and
from analog to digital at the receiving end. From a
conceptual standpoint, this explanation is sufficient.
However, if you are going to install a modem, you need
to know some of the technical aspects of modems.
Figure 2-3.—Digital data as it is encoded, modulated, transmitted, demodulated, and decoded.
2-3
are their higher installation costs and complex
maintenance.
Network Interface Card and Cabling
To attach personal computers to the LAN, you must
install a network interface card (NIC) into an empty
expansion slot in the PC, install the appropriate
software, and attach the network cable to the NIC. The
other item you need to consider is what type of
connector to use. But before deciding the type of
connector to use, you need to know what type of cable
and architecture you will be using. The cables may be
twisted-pair cable, fiber optic cable, or coaxial cable.
The connector provides the physical link between
two components. For example, a connector can link a
cable and a NIC, a cable and a transceiver, or two cable
segments.
Twisted-pair cable The twisted-pair cable is
easy to install and costs little on a per-foot basis. In
some cases existing telephone cable may be used. Its
disadvantages include limitations in capacity and
speed. It is also susceptible to electrical interference
unless it is shielded.
Connectors differ in their shape, size, gender,
connection mechanism, and function. These features
influence and determine where a connector can be used.
Where necessary, special adapters may be used for
connections involving different connector
combinations.
Fiber optic cable Fiber optic cable is the best
choice if a secure network is needed. Because the cable
transmits light, the transmissions are immune to
interference caused by electrical or electronic devices.
Also, if your network will run through an area of heavy
industrial activity or a work place with strong radio
frequency interference, fiber optic cable is the most
appropriate choice. Other advantages of the fiberoptic
cable are that it lasts longer than other cable and can
carry many more channels. Its disadvantages include its
high price, poor connectivity, and low flexibility.
Connectors also differ in how sturdy they are, how
easily and how often they can be attached and detached,
and in how much signal loss there is at the connection
point.
Connectors
The type of connector needed in a particular
situation depends on the components involved and, for
networks, on the type of cable and architecture being
used.
CONNECTOR FUNCTIONS.— A connector
may be passing the signal along or absorbing it. A
connector that passes a signal along may pass it
unmodified or may clean and boost it. Connectors can
serve a variety of purposes, including the following:
Coaxial cable Coaxial cable, also called coax,
networks have gained in popularity because of their use
in cable television. The quantities of cable and
connectors produced for cable television have greatly
reduced the prices of these components for network
users. Coaxial cable comes in various thicknesses and
is designated by a number: RG-11, RG-58, RG-59,
RG-62, etc. You can use either baseband or broadband
transmission methods with coaxial cable.
Connect equal components, such as two
segments of thin coaxial cable
Connect almost equal components, such as thin
to thick coaxial cable
Baseband coaxial systems, which transmit digital
signals unchanged over a single channel, have several
advantages. They are inexpensive, simple, easy to
install, and have low maintenance. They also allow
very high data transmission rates. One disadvantage is
they are limited to transmitting digital signals only.
Connect unequal components, such as coaxial to
twisted-pair cable
In contrast, broadband coaxial systems require
the digital signal to be converted to an analog signal
before transmission and then back to digital by modem
at the receiving device. Broadband systems support
data, voice, and video signals that may be transmitted
simultaneously. Disadvantages of broadband systems
CONNECTOR SHAPES.— Specially shaped
connectors are used for particular types of connections
or for connections in particular locations. For example,
a T-connector attaches a device to a cable segment; an
elbow connector allows wiring to meet in a corner or at a
wall.
Connect complementary components, such as a
NIC to a network
Terminate a segment
2-4
Figure 2-4.—Connector shapes.
Table 2-1.—Cable connector shapes.
Table 2-2.—Fiber-optic connectors.
In addition to attachment mechanisms, fiber-optic
connectors differ in the following ways:
The connector shapes used in networking setups are
listed in table 2-1. Figure 2-4 shows examples of
connector shapes.
The size of the ferrule.
FIBER-OPTIC CONNECTORS.— Like
electrical cable connectors, different types of fiberoptic connectors have different kinds of attachment
mechanisms. The actual attachments between ferrule
shells may be made by threading, snapping, or clicking.
Table 2-2 lists the most commons types of fiber-optic
connectors.
Whether the connector can be keyed. This is the
technique for making a connector asymmetrical,
usually by adding a notch or plug, making it
impossible to plug the connector in wrong.
The number of matings the connectors can
handle without producing unacceptable signal
loss.
2-5
INSPECTING COMPONENTS
Whether the fiber must be twisted to make the
connection; multiple fibers cannot run through
the same connector if it is to be twisted.
The inspection of the components when they are
received is limited to checking for any physical damage.
This damage will include:
The connectors differ in the way the fiber is
attached to the connector itself. You can either use
epoxy to glue the fiber into the connector, or you can
crimp the connector and the ferrule together using a
special crimping tool.
Any damage to the packing material
Damage to the case
Hidden damage on the inside of the cabinet
CONNECTOR GENDERS.— Connector gender
basically refers to whether a connector has plugs or
sockets. The gender is important because the elements
being connected must have complementary genders.
The inspection that is conducted needs to be as
thorough as possible, since any damage discovered
must be reported to the supplier. This inspection also
needs to be accomplished as soon as the equipment
arrives, because the longer you wait, the less likely it
becomes that the supplier will replace the equipment.
A male connector is known as a plug; the female
connector is known as a jack. With a few exceptions,
such as the IBM® data connectors and certain fiberoptic connectors, all connector types have distinct
genders. Figure 2-5 shows examples of male and
female connectors.
NETWORK TESTING
Network testing is changing significantly because
of the growth of digital network capability. Testing in
the voice network has always been considered as much
of an art as a science because of the variable nature of
the different impairments encountered. The digital
net work has been designed with more diagnostic
capability, making it much easier to identify and isolate
problems. The testing is done in the carrier
environment, not in the user environment.
CONNECTOR MECHANISMS.— The
connection mechanism defines how the physical
contact is made to allow the signal to pass from one side
of the connection to the other.
Connection mechanisms differ in how sturdy they
are. For example, the pin-and-socket connection at a
serial port can be wobbly without extra support from the
screws on either side of the plug. On the other hand,
fiber-optic connectors must be cut to precise
proportions and must not allow any play in the
connection.
Network Testing Methods
There are three basic approaches to network testing,
as follows:
Figure 2-5.—Connector genders.
2-6
1. Rely on vendors. If you rely on a vendor for
testing, you probably have a single vendor’s products in
your network and are, therefore, locked into that vendor.
Fewer vendors today are capable of providing this
complete capability.
Construction tools for assembling and
disassembling systems; for example,
screwdrivers, pliers, chip removers, and chip
installers.
2. Use an organization dedicated to network
problem solving (third party). At one time, third-party
problem solving was considered a viable alternative,
but today the expertise needed is so vast and covers such
a wide variety of products that it is not feasible to
provide the service. The carrier providing the majority
of your circuits is the best for handling your network
management. However, it is difficult for the carrier to
be objective, and it is usually not very cost effective.
Testing tools for testing individual components
or for monitoring the performance of a
component or system, such as voltmeters,
ammeters, and line scanners.
3. Use in-house network management. In-house
network control is by far the most flexible in design and
operation. Network administrators typically
understand their problems better than any carrier or
vendor could. Network problems are not always the
result of network conditions; they may actually be
operational problems. A disadvantage of in-house
network control is that it requires more resources, such
as knowledgeable people, equipment, space, and all of
the other support overhead.
BASIC TOOLS.— The level and range of tools
you will need depends on the level of your involvement
with the network. Regardless of the level, a few basic
tools will almost certainly make your life easier:
Regardless of the testing method that is used,
testing can be performed by both hardware tools and
software programs.
Wrenches or nut drivers, for tightening and
loosening nuts;
Safety tools for making sure components are
protected against damage from electrical and
other dangers; for example, static cords,
electrical mats, and shorting probes.
Screwdrivers, for opening machines, installing
and removing expansion cards, and for attaching
connectors;
Pliers, for grasping objects;
Chip removers/installers, for removing and
installing computer chips; and
Hardware Testing
Tweezers, for retrieving small parts and screws.
The tools used are partly insurance and partly
convenience devices. The greatest expense of a
network comes when it is down or functioning
incorrectly; it is important to be able to test components
when things go wrong. Testing should also be
accomplished before installing, to ensure that you do
not install a faulty component. After they are installed,
test components periodically to make sure they are
functioning properly. Special tool are available for this
purpose.
In addition to these tools, some people might also
have wire strippers, cutters, and soldering irons that can
be used to set up special-purpose circuits or wiring
connectors.
If you are going to do any troubleshooting at all, you
will need a voltmeter or ammeter (probably both), with
an operator’s manual, to test the electrical activity. Use
of the manual is essential to connect the meter properly;
connecting the meter wrong can cause serious damage
to sensitive circuitry.
Network testers can be very expensive, while
convenience tools, such as wire crimpers and
voltmeters, are quite inexpensive. The amount that is
spent on tools will depend on the size of the network, the
importance of the network’s contents, and who will be
doing the maintenance on the network.
TOOLS FOR INSTALLING AND
ATTACHING CABLE.— The tools used in making
cables are specialized tools. They are used to attach the
connectors onto the cable and then to test the cable. It is
advisable to get the cables pre-made to the desired
length by the manufacturer. Unfortunately, that isn’t
always possible.
The following are several types of hardware tools:
Manufacturing tools for creating individual
components, such as crimpers and dies for
attaching wires to connectors.
To attach connectors to cable, you need the
following tools:
2-7
inefficiencies and bottlenecks, so they can be
elimated. While monitoring the system’s
performance, keep careful track of the following:
a crimping tool, for pressing the cable and
connector together, and
a die for the specified cable/connection pair, to
make sure cable and connector fit properly.
Operating costs
Threats to security
Installation tool kits that include the crimping tool,
die, cable, connectors, and cable ties can be purchased
from manufacturers. These kits range in price from one
or two hundred to several thousand dollars.
User satisfaction
User productivity
TOOLS FOR TESTING CABLES.— Voltmeters
and ammeters provide readings of voltage and current,
or amperage by tapping into the circuit and recording
the electrical activity as it occurs. These recorded values
may or may not provide the details about what is
happening along the lines of the network.
Track these areas especially during the first few
weeks after the network is installed. Do not be surprised
if some of these measured indicators change drastically
during this period. For example, costs may drop
drastically after the startup period, while user
satisfaction and productivity may rise after the initial
problems are resolved.
Scanners are much more sophisticated testing tools.
Some of the capabilities of scanners include the
following:
NETWORK PHYSICAL CONNECTIONS
Check for faults in a cable.
A network connection is a linkage between network
elements. Physical connections concern the cables and
connectors used to create the physical layout of the
network. When building a network, you must first
establish the physical connections.
Test a cable’s compliance with network
architectures.
Monitor performance and electrical activity,
given the type of cable and architecture
involved.
NETWORK BACKBONES
Backbone cable refers to the cable that forms the
main trunk, or backbone, of a network. Individual
nodes and other devices may be connected to this cable
using special adapters and a separate stretch of cable.
Test the cable’s wiring sequence.
Generate and print a summary of the information
obtained from the tests.
Backbone cable is defined by the Electronics
Industries Association/Telecommunications Industry
Association-568 (EIA/TIA-568) committee as any
“behind the scenes” cable; that is, cable running behind
walls, in shafts, or under the ground.
A powerful scanner can test for cable quality, for the
quality of the connections between cable segments, or
between cable and device. A less poweful scanner will
be able to test for noise, crosstalk, signal attenuation,
resistance, cable length, and so on.
The EIA/TIA-568 recognizes four types of
backbone cable; they are listed in table 2-3.
Software Testing
Diagnostic software can be used to help anticipate
or catch problems early and to help deal with the
problems once they have arisen. Network versions of
diagnostic software may be expensive, but they can
save the system under some circumstances. For
example, virus detection software can save hours of
reconstruction and reloading the system. Using
software to test the hard disk can identify bad disk
sectors before data can be written to them and move any
data from bad sectors to a safe location.
The use of a backbone network to tie together a
number of small access networks offers several
advantages over the construction of a single large LAN.
The various LANs connected to the backbone are able
to operate in parallel, providing greater processing
efficiency. The multiple-network approach is also more
reliable, since each individual LAN can continue
operating if one of the access networks, or even the
backbone, fails. The backbone network must also be
highly reliable, since the greater distances covered may
make it difficult to locate and repair faults. The LANs
that connect to the backbone must be flexible and lowcost in terms of installation and user connection.
Another use of diagnostic software is performance
monitoring and analysis, which involves tracking the
networks behavior. This will help to identify
2-8
Table 2-3.—Types of backbone cable.
To connect a node directly to a backbone, you
would use a drop cable for the connection. Nodes are
normally connected to the backbone indirectly through
a concentrator or a hub rather than with a drop cable.
The elements needed to connect a node to a network
include the following:
Cable: twisted-pair, coaxial, or fiber-optic
Wiring centers: hubs or concentrators
Intranetwork links: connectors, repeaters, and so
on
Internetwork links: bridges, routers, gateways,
and so on
The cable provides a transmission medium, as well
as the physical link between the nodes on the network.
Connectors and repeaters attach cable sections to each
other; connectors and transceivers attach NICs to a
cable and, thereby, to the network. Transceivers enable
different types of cable to be attached to each other.
Terminators absorb a transmission at the end of a
network, preventing the signal from traveling back in
the other direction on the network. The types of
intranetwork links allowed in the network depend on
the type of cable used and on the network topology
used.
Connection to the backbone network may require a
bridge, router, gateway, concentrator or hub, depending
on the architectures of the various LANs and the
backbone itself. The connectors used will also depend
on the type of cable used for the backbone. If the
backbone is coaxial cable, you would use a T-connector
and barrel connectors to make the connection to another
cable or a hardware device.
The backbone manages the bulk of the traffic, and it
may connect several different locations, buildings, and
even smaller networks. The backbone often uses a
higher-speed protocol than the individual local area
network (LAN) segments.
Wiring centers serve as a focal point for network
elements, and may influence the logical arrangement of
nodes on the network.
Internetwork links may be bridges, routers,
gateways, and soon. Such components serve to connect
networks to each other. The type of internetwork link
depends on whether the two networks are the same or
not, and the amount of translation that is needed.
One obstacle to a successful backbone network is
the high bandwidth that may be required to handle
potentially heavy traffic. Because of this consideration,
fiber-optic cable is the most sensible cabling for
backbone networks.
NODES
NETWORK SERVER
A server is the central computer in a network, and is
responsible for managing the network. The server
provides some type of network service. It may be
hardware, such as a file server, or software, such as
network level protocol for a transport level client.
The computers, or nodes, in a network may be used
for workstations, servers, or both. PCs need a network
interface card (NIC) installed for networking
capabilities.
The NICs mediate between the computer and the
network by doing the necessary processing and
translation to enable users to send or receive commands
and data over the network. NICs are designed to
support a particular network architecture, such as
Ethernet® or ARCnet®.
The server provides its service to other
workstations on the network or to other processes. In a
server-based network, the most important hardware
server is the fileserver, which controls access to the files
and data stored on one or more hard disks.
2-9
A server may be dedicated or nondedicated.
Dedicated servers are used only as a server, not as a
workstation. Nondedicated servers are used both as a
server and a workstation. Networks with a dedicated
server are known as server-based networks; those with
nondedicated servers are known as peer-to peer
networks.
DEDICATED SERVERS
Many of the NOSs that allow the nondedicated
server to run with DOS make them extremely
slow and clumsy. While most dedicated servers
have software that replaces DOS, such systems
may also require a separate non-DOS partition
on the hard disk. This allows the NOS to arrange
and deal with the contents of the partition in a
way that optimizes performance.
Dedicated servers cannot be used for ordinary
work. In fact, access to the server is often limited to
prevent any access by unauthorized users.
Running applications on a DOS machine while it
is also supposed to be running a network can lead
to a deadly performance degradation.
Most of the high-end network packages assume you
are using a dedicated server. If the network has a
dedicated server, it is most likely a file server.
Certain tasks will tie up a DOS machine,
effectively stopping the network until the task is
finished.
A dedicated fileserver runs the NOS software, and
workstations run smaller programs whose function is to
direct user commands to the workstation’s operating
system or to the server. Both servers and workstations
need NICs to function on the network.
Adequate security is more difficult to maintain
on a nondedicated server.
SUMMARY
NONDEDICATED SERVERS
In this chapter we discussed the different types of
network components and their functions. We described
cabling and the connectors used to connect the network
hardware. We covered the purpose of the server and the
differences between a dedicated and a nondedicated
server. Remember, the driving factor for the type of
hardware and cabling used is the topology of the
network.
A nondedicated server can be used as a workstation
as well as a server. Using a server as a workstation has
several disadvantages and is not advisable for larger
networks.
The following are disadvantages of nondedicated
servers as compared to dedicated servers:
2-10
CHAPTER 3
NETWORK TROUBLESHOOTING
Upon completing this chapter, you should be able to do the following:
Describe how to diagnose and isolate problems with LANs.
Describe how to troubleshoot network malfunctions.
Explain how to test and evaluate the connection of networking system nodes.
Explain how to troubleshoot communications line problems.
With any network system, you should have a set of
error procedures for personnel to follow to handle errors
or malfunctions on the system. These error procedures
are the steps to be taken when the system is not
operating properly. They are different from the errordetection and diagnostic procedures used to isolate and
correct transmission problems.
Workstation and server configurations
All network related software and equipment
Location and paths of all wiring
Updated records of all equipment and
configurations changes
A complete set of diagnostic procedures is
necessary for the system. The system procedures are
used to isolate the problem to the system or subsystem
level. Since the facilities of a network may not be in the
local area, it is necessary to have a set of test software
and equipment with replacement components available
for diagnosing and correcting problems.
With documentation in hand, along with the help of
diagnostic software (a network management package or
a LAN analyzer), and specialized diagnostic
equipment, such as a datascope, a time domain
reflectometer (TDR), or a breakout box, the job
becomes routine.
Classifying the problems and taking the necessary
actions to resolve them are an important part of your job
as a troubleshooter. However, it is equally important to
remember to log all problems according to your
activity’s procedures. This will identify recurring
problems, provide information for long term solutions,
and enhance your command’s training program.
TROUBLESHOOTING LANS
As a communications specialist, more than likely
you will be expected to know how to troubleshoot
problems on LANs. As a troubleshooter, you must be
able to identify a wide range of network problems
relating to hardware (the data terminal equipment, the
communications link, repeaters, gateways, and so on),
software (network operating system, applications, and
soon), and peopleware (the end user). It will be your job
to identify, isolate, and resolve both the simple and
complex problems.
ISOLATING PROBLEMS
When isolating a problem, consider the three major
areas we discussed earlier-the user, the software, and
the hardware, usually in that order. The majority of all
network-related problems are caused by the user’s
actions—operator errors. Users either do not
understand how to operate their PC in a networking
environment or they are unfamiliar with the application
software package they are using. Most of the time you
will find yourself responding to user problems and
complaints. A user will call, saying such things as the
following:
DIAGNOSTIC TOOLS
Normally, a problem can be solved without too
much difficulty with the help of diagnostic tools. The
best diagnostic tool available is accurate
documentation. This documentation should include:
3-1
likely the result of an inexperienced operator (user
error). The logical corrective action to take is to walk
PO3 Frost through the proper log-on procedures and
password security requirements. He follows your
instructions and successfully logs onto the LAN. PO3
Frost should have been able to log onto the LAN by
following the User’s Guide on LAN operations. You
might want to review the guide to make sure it is current
and available to all users.
My terminal/PC is hung up, and I cannot get into
the system.
My terminal/PC screen suddenly went blank.
My temninal/PC keeps coming up with the same
error message.
My terminal/PC will not allow me to access the
disk file.
A few weeks later PO3 Frost calls again and reports
he has been having intermittent problems while logged
on to the LAN. Sometimes while he is saving or
retrieving data, his machine locks up for no apparent
reason. Again, no one in his immediate work area is
experiencing problems. After obtaining all the
pertinent information available, you believe the
problem is faulty hardware. During the save and
retrieve operations, a packet is generated and sent
through the network interface card, onto the cable, and
to its destination. So the two most logical components
to check are the cable connections and the network
interface card. The diagnostic tools to use are the time
domain reflectometer (TDR) to check any breaks on the
cable and the diagnostics that come with the interface
card. PO3 Frost runs the card diagnostics at the terminal
while you check the cable continuity. The network card
passes the test, but the TDR detects a continuity break
near his location. A LAN technician checks the
connectors at the workstation and discovers one of the
connectors has worked itself loose. After replacing the
connector, the cable is tested again and passes. PO3
Frost logs on to the LAN and experiences no further
problems. In this example we eliminated the cable itself
because no other user on the cable segment was
experiencing problems. Had there been other users also
experiencing intermittent failures, then the cable would
have immediately been our focal point of testing, since
this is the commonality between the users.
My terminal/PC will not print.
It will be your job to determine if the problem is
user, software, or hardware related. Whenever you
receive a call about a problem, obtain as much
information as possible about the person and the
problem. Ask the user’s name, phone number, the
terminal/PC or node identification number, the nature
of the problem, and what, if anything, occurred
immediately preceding the problem. In addition, you
should ask the user what application he or she was
trying to access or currently working with at the time the
problem occured. Ask whether other users are
experiencing the same or similar problem, did any error
messages appear on the screen, and be sure to ask
whether the PC was moved before the problem
occured. Sometimes moving hardware creates
problems—the connector cable may not be seated
properly.
Once you have received initial information about a
problem, it should help you to categorize the problem.
Keep in mind most problems are the result of
inexperienced users/operators. Because so many
different types of errors can occur, it would be
impossible for us to list them all, along with the
necessary steps to resolve them. However, based on
past experiences, we can provide you with some helpful
hints and guidelines to follow. If the problem seems to
be isolated to one user, it is probably user error; if the
problem occurs with a group of users in a common
geographic location, the problem is usually related to
the cable; and if the problem is network wide, a close
look at the network software is in order. Let us take a
look at some of the more common problems that
frequently occur and their solutions in connection with
these three categories.
You arrive at work Tuesday morning and find a
stack of messages waiting for you from users
experiencing problems while trying to access the word
processing program on the LAN. The only thing these
users have in common is they all use the same file
server. Immediately you focus your attention on the
network operating system and software. You call PO3
Door to ask her a few questions before you begin
troubleshooting any further. You learn PO3 Door is able
to access all application programs on the LAN with the
exception of the word processing program. You
immediately log on to the network management
program and monitor the data traffic. You discover no
user has used the word processing program since
PO3 Frost has just called to report he cannot log on
to the LAN. You begin solving the problem by asking
some preliminary questions. You find this is the first
time PO3 Frost has used the LAN and no one else in his
area is experiencing any problems. At this point, you
should be able to recognize the problem is more than
3-2
Monday at 1600. The only person authorized to use the
LAN after 1600 is PO1 Brush, who is the network
administrator. You call PO1 Brush and ask if any
changes were made to the word processing program
since yesterday. PO1 Brush states he installed a new
version of the word processing program on Monday
around 2200 to eliminate any work disruptions. You ask
him to check the security access to this new version.
You find PO1 Brush inadvertently restricted all users
from accessing the new version of the word processing
program after he removed the old one. He makes the
necessary access changes, and everybody is once again
happy and able to use the new version.
Most computers run a simple set of system checks
when the computer is turned on. The PC tests are stored
in read-only memory (ROM), and are known as poweron self tests (POSTs). If a POST detects an error
condition, the computer will stop and display an error
on the screen. Some computers will emit a beep signal
to indicate the type of error.
One of the best tools to use for network
malfunctions is a network analyzer. A network analyzer
is a product that can be used to monitor the activity of a
network and the stations on it, and to provide daily
summaries or long-term trends of network usage and
performance. A network analyzer can do tasks such as:
As you can see, there is a pattern to the various types
of errors/problems you will encounter. The problems
you will be confronted with will range from the simple
to the disastrous. They may be user/operator errors,
software problems, or hardware malfunctions.
Knowing which is sometimes easy. Under other
conditions, it may be difficult for you to determine the
source of the problem. The important thing is to learn
from your past experiences. Keep a list of symptoms,
probable causes, and ways you can use to trace a
problem to its cause. This will assist you in diagnosing
and troubleshooting problems. You will also find users
have a tendency to make the same mistakes again and
again, especially while they are learning. You can
provide them a great service by explaining some of the
more common problems they are likely to encounter,
the reasons for the problems, and ways to avoid having
them happen to them.
Count or filter network traffic.
Analyze network activity involving specified
protocols or frame structures.
Generate, display, and print statistics about
network activity, either as they are being
generated or in summary form.
Send alarms to a network supervisor or network
management program if any of the statistics
being monitored exceeds predetermined limits.
Do trend or pattern analyses of network activity.
Network analyzers may be software only or consist
of both software and hardware. The latter may include
an interface card enabling you to test the network
directly. This card may include an on-board processor.
Because of their greater capabilities, hardware/software
analyzers are more expensive than the software only
analyzers. In fact, the prices for the hardware/software
analyzers can be several times as high as those for the
software only versions.
NETWORK MALFUNCTIONS
Any malfunction of the network is going to result in
a nonavailability of the system to the users. The
diagnosis and fixing of this malfunction becomes a high
priority. There are three primary culprits to network
malfunctions: component and server failures, and data
collisions.
SERVER FAILURE
The most obvious sign that the server has failed for
some reason is that all users, except root, will not be able
to logon to the system. Use the following steps as
required to reestablish services:
COMPONENT FAILURE
Component failures are categorized in two
categories: hard faults and soft faults. Hard faults are
relatively easy to find, and a diagnostic program will
diagnose them correctly every time. Soft faults can be
difficult to find, because they occur sporadically or only
under specific circumstances, rather than every time the
memory location is tested. A diagnostic program tests
computer hardware and peripheral devices for correct
operation.
The first and easiest thing to try is to run the
system distribution again. This will rebuild the
system maps if nothing else is wrong and will
allow users access to the system.
Shutdown and reboot the system. During the
boot process ensure that no failures occur on any
of the nodes.
3-3
than expected indicates a collision, since this means
there are multiple signals traveling along the backbone
at the same time.
Verify the domain name.
Look for the maps subdirectory; it should be the
same as the domain name. If it is not there, you
will need to run the system initialization
command.
In a CSMA/CD (carrier sense multiple access with
collision detection) systems, all workstations or nodes
attached to the network monitor the transmission
medium at all times. When a node needs to send data, it
waits until the line is quiet and then transmits. If two or
more nodes happen to transmit data at the same instant,
a collision occurs. Each node detects the collision and
then waits for a variable amount of time (as
programmed in the NIC’s microprocessor) before
testing the bus again and retransmitting. Since each
node waits for a different amount of time, say 10/1000
and 20/1000 of a second, it is very unlikely that the
collision will occur a second time. The CSMA/CD
detection method is further illustrated in figure 3-1.
If the above fails, ensure that all the files to be
mapped are present on the server. If any have
been deleted, they will have to be restored from
the latest system saves.
One of the best ways to avoid server malfunctions is
to conduct maintenance on the server. It is important to
set up a schedule for your server and strictly adhere to it.
To check the hardware, you should do at least the
following things:
Clean the server carefully but thoroughly.
Collision Avoidance
Check cabling and connections for tightness and
signs of bending or stress. Do not disconnect
connectors unless necessary, since many
connectors are rated for a limited number of
matings.
To avoid collisions, nodes can send special signals
that indicate a line is being used for a transmission. In a
If possible, check the cabling with a line
analyzer.
Run thorough diagnostics on the storage medium
and on other system components to identify the
components that are likely to fail and to deal with
these before they actually do fail.
Check the quality of your power line by using a
line tester.
The hardest part of server maintenance is finding
the time to conduct the maintenance, since the network
will have to be offline to conduct. In many cases, server
maintenance will need to be during off peak hours, late
night or early morning, when there is little or no use.
DATA COLLISIONS
A data collision is the simultaneous presence of
signals from two nodes on the network. A collision can
occur when two nodes each think the network is idle and
both start transmitting at the same time. Both packets
involved in a collision are broken into fragments and
must be retransmitted.
Collision Detection
To detect for a collision, nodes check the dc voltage
on the line. A voltage level of two or more times higher
Figure 3-1.—A bus network using the CSMA/CD access
method.
3-4
CSMA/CA (carrier sense multiple access with collision
avoidance) system, the media-access method uses RTS
(ready to send) and CTS (clear to send) signals before
sending a frame onto the network. A node transmits
only after the node has requested access to the line and
access has been granted. Other nodes will be aware of
the RTS/CTS transmission and will not try to transmit at
the same time.
Impulse noise: voltage increases that last for just
a short period, usually for only a few
milliseconds.
RTS.— A hardware signal sent from a potential
transmitter to a destination to indicate that the
transmitter wishes to begin a transmission. If the
receiver is ready, it sends a CTS signal in return.
There are limits set on the allowable levels for each
of these types of noise. A noise filter can be used to
remove random noise from a signal.
White noise: random background noise.
Crosstalk: interference on one wire from
another.
In a transmission, signal-to-noise ratio (SNR) is the
ratio between the signal and noise levels at a given
point, usually at the receiving end of the transmission.
The SNR value is generally expressed in dB.
CTS.— A hardware signal sent from a receiver to a
transmitter to indicate that the transmitter can begin
sending. ACTS signal is generally sent in response to
an RTS signal from the transmitter.
The SNR can be used to determine how long a cable
segment can be before the signal loss is unacceptably
high. The SNR also helps to determine whether a
particular type of cable will work for the intended use.
Cable testers can help determine whether a particular
type of cable is appropriate in a specific environment.
NETWORK SYSTEM CONNECTIONS
The testing and evaluation of network connections
is accomplished with the same test equipment that is
used to test network components. This equipment
includes voltmeters, ammeters, volt-ohmmilliammeters, and line scanners. All of this test
equipment checks the voltage, resistance, and current
that passes through the cable and the connectors
between the network nodes. Any increase or decrease in
voltage or current or an increase in the resistance will
cause communications problems for the users.
In general, digital signals have a much higher SNR
than analog signals. Because analog signals in a
broadband network must be confined to a portion of the
total bandwidth, filtering and other signal-cleaning
measures are necessary This confinement makes the
signal more delicate and subject to distortion.
Several types of filtering maybe used to help clean
a broadband transmission. The filters are distinguished
by the filtering technique they use as well as by where in
the transmission process they are applied.
Whether the cable is pre-made or you make it, you
should always test the cable before it installed into the
network. This will alleviate the possibility of installing
a bad cable or connector to the system. Any time that
you can detect a bad connector will be to your
advantage, since each connector has a limited number
of connections before it has to be replaced.
For example, filters applied early in the
transmission, prior to modulation, are known as
baseband or premodulation filters. Those applied after
the modulation are known as passband or
postmodulation filters.
COMMUNICATION LINE PROBLEMS
Communication line problems fall into three
general categories: excessive noise, cabling, and
backbone connections. With proper testing and
precautions, these problems can be taken care of before
they happen.
CABLING
Cables are good media for signals, but they are not
perfect. The signal at the end of the cable should be as
loud and clear as at the beginning, but this will not be
true.
EXCESSIVE NOISE
Any transmission consists of signal and noise
conponents. Even a digital signal degrades when
transmitted over a wire. This is because the binary
information must be converted to electrical form for
transmission, and because the shape of the electrical
signal changes over distance.
Noise is the term for random electrical signals that
become part of a transmission, and that serve to make
the signal (information) component of the transmission
more difficult to identify. Noise can take various forms,
including the following:
3-5
more necessary as transmission speeds increase. Two
types of line conditioning are available:
Signal quality degrades for several reasons,
including attenuation, crosstalk, and impedance.
C conditioning tries to minimize the effects of
distortion related to signal amplitude and
distortion due to envelope delay.
Attenuation
Attenuation is the decrease in signal strength,
measured in decibels (dB) per 100 feet. Such loss
happens as the signal travels over the wire. Attenuation
occurs more quickly at higher frequencies and when the
cable’s resistance is higher.
D conditioning tries to minimize the effects of
harmonic distortion in addition to the amplitude
and envelope delay distortions handled by type C
conditioning.
In networking environments, repeaters are
responsible for cleaning and boosting a signal before
passing it on. Many devices are repeaters without
explicitly saying so. For example, each node in a tokenring network acts as a repeater. Since attenuation is
sensitive to frequency, some situations require the use
of equalizers to boost different-frequency signals the
appropriate amount.
A line driver is a component that includes a
transmitter and a receiver; it is used to extend the
transmission range between devices that are connected
directly to each other. In some cases a line driver can be
used in place of a modem, for short distances of 10 miles
or less.
To test a particular section of cable, you can use a
line-testing tool. A line monitor is a low-end linetesting tool that tells you if the line is intact. A high-end
line-testing tool can do very precise measurements
using time domain reflectometry (TDR). A TDR is a
device used to test the integrity of a section of cable
before the cable is even unwound. This diagnostic
method uses a signal of a known amplitude and
duration, which is sent along a stretch of cable.
Depending on the amount of time the signal takes to
return and on the cable’s nominal velocity of
propagation, the TDR can determine the distance the
signal traveled and whether there are any shorts or
opens in the cable.
Crosstalk
Crosstalk is interference in the form of a signal from
a neighboring cable or circuit; for example, signals on
different pairs of twisted wires in a twisted pair cable
may interfere with each other. A commonly used
measure of this interference in twisted-pair cable is
near-end crosstalk (NEXT), which is represented in dB.
The higher the dB value, the less crosstalk and the better
is the cable.
Additional shielding between the carrier wire and
the outside world is the most common way to decrease
the effects of crosstalk.
Impedance
BACKBONE CONNECTIONS
Impedance, which is a measure of electrical
resistance, is not directly a factor in a cable’s
performance. However, impedance can become a
factor if it has different levels at different locations in a
network. In order to minimize the disruptive effects of
different impedances in a network, special devices,
called baluns, are used to equalize impedance at the
connection.
In addition to the inherent problems of the cabling,
backbone connections add the problems that come with
the use of connectors. They have only a limited number
of times that they can be connected before they have to
be replaced. These connectors are used in several
places along the backbone, each presenting one more
place for trouble to start. Some of the places that
connectors are used are:
Impedance does reflect performance indirectly.
The higher the impedance, the higher is the resistance;
the higher the resistance, the greater is the attenuation at
higher frequencies.
At the server
Line Conditioning
At the splice and coupler (used with fiberoptic)
At the repeater, concentrator, and the gateway
Along the backbone for each drop or tap
Each of the connections uses a different type of
connector, each with its own limitations. For example:
Line conditioning tries to eliminate the effects of
certain types of distortions on the signal. It becomes
3-6
SUMMARY
A vampire tap is a connector that uses two prongs
to pierce the cable to make its connection. When
it is used, one of the prongs can be bent and not
make a proper connection.
In this chapter we discussed the how to troubleshoot
communications line problems, network malfunctions,
and how to test and evaluate the connection of
networking system nodes. As with any
troubleshooting, individual manufacturers of both
hardware and software will have their own techniques
to follow. What we have tried to do is give you a brief
overview of the type of trouble that you can expect to
run into and some basics as how to begin the
troubleshooting.
An RJ connector is the same type of connector
used to plug your telephone into the wall. When
it is used, the plastic clip has a tendency to break
off the connector, resulting in the plug not
locking in place.
3-7
APPENDIX I
GLOSSARY
A
F
ATTENUATION— Loss of communication signal
energy.
FILTER— A device or program that separates data,
signals, or material in accordance with specified
criteria.
B
BASEBAND— The frequency band occupied by
individual information bearing signals before they
are combined with a carrier in the modulation
process.
FIREWALL— One or more components that control
the flow of network traffic between networks.
BISYNC— Controlling of data transmission by timing
signals generated at the sending and receiving
stations.
HANDSHAKING— The process through which the
rules for exchanging data over a communications
line are defined for the two devices involved.
BROADBAND— Transmission facilities whose
bandwidth is greater than that available on voicegrade facilities.
I
BUS— Channel or path for transferring data and
electrical signals.
INTERNATIONAL STANDARDS ORGANIZATION (ISO)— The international agency
responsible for developing standards for
information exchange.
H
IMPEDANCE— A measure of electrical resistance.
C
CARRIER SENSE MULTIPLE ACCESS
(CSMA)— A protocol that controls access to a
network’s bus.
INTERRUPT REQUEST LINES— Physical
connections between hardware devices and the
interrupt request.
CARRIER SENSE MULTIPLE ACCESS WITH
COLLISION AVOIDANCE (CSMA/CA)— A
protocol that requires carrier sense and in which a
data station that intends to transmit sends a jam
signal.
L
LINE DRIVER— A component that includes a
transmitter and a receiver.
CARRIER SENSE MULTIPLE ACCESS WITH
COLLISION DETECTION (CSMA/CD)— A
protocol that requires carrier sense and in which a
transmitting data station that detects another signal
while transmitting, stops sending, sends a jam
signal, and then waits for a variable time before
trying again.
LINK— The communications media used to connect
nodes.
M
MULTITASKING— A mode of operation that
provides for concurrent performance of two or
more tasks.
CLEAR TO SEND— A hardware signal sent from a
receiver to a transmitter to indicate that the
transmitter can begin sending.
N
NETWORK INTERFACE CARD (NIC)— The
expansion card that allows the workstation to
communicate with the network.
CROSSTALK— The disturbance caused in a circuit by
an unwanted transfer of energy from another
circuit.
AI-1
NETWORK OPERATING SYSTEM (NOS)— A
software package that makes it possible to
implement and control a network and that enables
users to make use of resources and services on that
network.
R
NODE— The point at the end of a branch.
S
NOISE— Random electrical signals that become part
of a transmission, and that serve to make the signal
(information) component of the transmission more
difficult to identify.
SYNCHRONOUS DATA LINK CONTROL
(SDLC)— Primary protocol supported under
System Network Architecture (SNA).
READY TO SEND— A hardware signal sent from a
potential transmitter to a destination to indicate that
the transmitter wishes to begin a transmission.
SIGNAL-TO-NOISE RATIO (SNR)— The ratio
between the signal and noise levels at a given point,
usually at the receiving end of the transmission.
O
OPEN SYSTEMS INTERCONNECTION
(OSI)— The networking standard for
interconnecting dissimilar computer systems.
T
TIME DOMAIN REFLECTOMETER— A device
used to test the integrity of a section of cable.
P
PROTOCOL— A formal set of conventions governing
the format and control of inputs and outputs
between two communicating processes.
TOPOLOGY— The physical or logical layout of a
LAN.
AI-2
APPENDIX II
GLOSSARY OF ACRONYMS AND
ABBREVIATIONS
A
I
AWG— American wire gauge.
IP— Intemet protocol.
B
IRQ— Intermpt request line.
Bisync— Binary synchronous communications
protocol.
ISO— International Standards Organization.
BNC— Barrel nut connector.
bps— Bits per second.
C
CAD— Computer aided design.
CODEC— Coder/decoder.
CSMA— Carrier sense multiple access.
L
LAN— Local area network
LED— Light-emitting diode.
M
MAN— Metropolitan area network.
MAU— Multistation access unit.
Mbps— Megabits per second.
CSMA/CA— Carrier sense multiple access with
collision avoidance.
MIC— Medium interface connector.
MODEM— Modulator-demodulator.
CSMA/CD— Carrier sense multiple access with
collision detection.
N
CTS— Clear to send.
NEXT— Near-end crosstalk.
D
NIC— Network interface card.
dB— Decibel.
NOS— Network operating system.
O
E
OSI— Open systems interconnection.
EIA/TIA— Electronics Industries Association/
Telecommunications Industry Association.
P
POST— Power-on self test.
F
R
FSCK— Filesystem check.
RJ— Registered jack.
FTP— File transfer protocol.
ROM— Read-only memory.
G
RTS— Ready to send.
S
Gbps— Gigabits per second.
SC— Subscriber connector.
H
SDLC— Synchronous data link control.
HTTP— Hypertext transfer protocol.
SMA— Sub-miniature assembly.
AII-1
SNR— Signal-to-noise ratio.
TELNET— Telecommunications network.
ST— Straight tip.
U
STP— Shielded twisted pair.
UDP— User datagram protocol.
T
UTP— Unshielded twisted pair.
TCP— Transmission control protocol.
W
TDR— Time domain reflectometer.
WAN— Wide area network.
AII-2
APPENDIX Ill
REFERENCES USED TO
DEVELOP THE TRAMAN
Feibel, Werner, Novell’s® Complete Encyclopedia of Networking, Sybex Inc.,
Alameda, CA, 1995.
Gibbs, Mark, Absolute Beginner’s Guide to Networking, Second Edition, Sams
Publishing, Indianapolis, IN 1995.
Liebing, Edward, NetWare User’s Guide, M & T Books, New York, NY, 1993.
Lowe, Doug, Networking For Dummies, IDG Books Worldwide, Inc., Foster City,
CA, 1994.
Martin, James, Local Area Networks Architectures and Implementations, Prentice
Hall, Englewood Cliffs, NJ, 1989.
Ported SNAP I/II System Administration Manual TAC-3 Version, NAVMASSO
Document Number 54-94-1, Navy Management System Support Office,
Chesapeake, VA, 1994.
Sherman, Ken, Data Communications User’s Guide, Third Edition, Prentice Hall,
Englewood Cliffs, NJ, 1990.
AIII-1
INDEX
A
D
Access methods, 1-12
Data collisions, 3-4
contention, 1-12
avoidance, 3-4
network standards, 1-13
detection, 3-4
token passing, 1-13
E
Analyze configuration, 1-6
Excessive noise, 3-5
crosstalk, 3-5
C
impulse, 3-5
Cabling, 1-15, 3-5
white, 3-5
cable selection, 1-17
F
coaxial, 1-16, 2-4 .
excessive noise, 3-5
Firewalls, 1-18
application layer, 1-18
fiber optic, 1-17, 2-4
choosing, 1-19
impedance, 3-6
packet filters, 1-18
line conditioning, 3-6
twisted-wire pairs, 1-16, 2-4
Coaxial, 1-16, 2-4
H
Hardware testing, 2-7
baseband, 2-4
basic tools, 2-7
broadband, 2-4
tools for installing cable, 2-7
tools for testing cables, 2-8
Collision avoidance, 3-4
CTS, 3-5
RTS, 3-5
Communication line problems, 3-5
I
Install components, 2-1
bridges, 2-2
attenuation, 3-6
brouters, 2-2
backbone connections, 3-6
concentrators, 2-3
cabling, 3-5
connectors, 2-4
Connectors, 2-4
gateways, 2-2
function, 2-4
hubs, 2-3
genders, 2-6
modems, 2-3
mechanisms, 2-6
network interface card, 2-4
shapes, 2-4
repeaters, 2-1
Crosstalk, 1-16, 3-6
routers, 2-2
INDEX-1
L
Network operations, 1-1
LAN configurations, 1-9
server failure, 3-3
bus, 1-10
monitor, 1-3
distributed tree, 1-11
network startup/shutdown, 1-2
ring, 1-11
remote terminals, 1-2
star, 1-9
review audit logs, 1-4
Links, 1-1
Network parameters, 1-5
modifying, 1-5
M
setting, 1-5
Monitor, 1-3
Network physical connections, 2-8
backbones, 2-8,3-6
N
Network analyzer, 3-3
Network components, 2-1
inspecting, 2-6
install, 2-1
nodes, 2-9
Network port configuration, 1-5
port address or name, 1-5
Network server, 2-9
dedicated, 2-10
testing, 2-6
Network configurations, 1-4
analyze configuration, 1-6
nondedicated, 2-10
Network software, 1-6
application, 1-7
network parameters, 1-5
installation, 1-7
network port configuration, 1-5
testing, 1-8
software configurations, 1-5
restoration, 1-8
system parameters, 1-4
system resource limits, 1-6
Network design, 1-9
system, 1-6
Network startup/shutdown, 1-2
system shutdown, 1-3
access methods, 1-12
cabling, 1-15
system startup, 1-2
Network testing, 2-6
calculating capacity, 1-9
hardware, 2-7, 3-5
firewalls, 1-18
methods, 2-6
LAN configurations, 1-9
network operating system, 1-18
operating system, 1-18
software, 2-8
Nodes, 1-1
protocols, 1-12
requests, 1-9
O
Network malfunctions, 3-3
OSI model, 1-13
component failure, 3-3
layer 1, 1-14
data collision, 3-4
layer 2, 1-14
INDEX-2
OSI model—Continued
S
layer 3, 1-14
System modes, 1-3
layer 4, 1-15
multi-user, 1-3
layer 5, 1-15
single-user, 1-3
layer 6, 1-15
System parameters, 1-4
layer 7, 1-15
hardware interrupt, 1-4
software interrupt, 1-4
P
System resource limits, 1-6
hardware, 1-6
Protocols, 1-12
software, 1-6
Bisync, 1-12
SDLC, 1-12
System restoration, 1-8
reconfiguration, 1-8
redundancy, 1-8
R
rerouting, 1-8
Reboot, 1-3
T
Remote Terminals, 1-2
Troubleshooting, 3-1
logins, 1-2
diagnostic tools, 3-1
remote console, 1-2
isolating problems, 3-1
INDEX-3
Assignment Questions
Information: The text pages that you are to study are
provided at the beginning of the assignment questions.
ASSIGNMENT 1
Textbook Assignment: “Network Administration,” chapter 1, pages 1-1 through
1-19.
1-1.
Networking gives an
individual the capability to
communicate and connect with
another individual or
another system in order to
accomplish which of the
following tasks?
1.
2.
3.
4.
1-2.
1-4.
2.
3.
Send messages
Share resources
Extend processing
Perform multiprocessing
4.
1-6.
2.
3.
4.
Coaxial
Fiber optic
Solid core
Twisted-pair
1-7.
1-8.
The first thing that the
initialization program
checks is which of the
following areas?
1.
2.
3.
4.
1
Five
Two
Six
Four
When shutting down the
system, turning off the
power to the CPU is
recommended under which of
the following times or
conditions?
1.
2.
3.
4.
Connections
Memory
Peripherals
User accounts
One
Two
Three
Four
Rebooting the system is
called for in how many
common situations?
1.
2.
3.
4.
Dialup access
Distance access
Extended access
Remote access
Establishes
communications
Initializes the system
Mounts and initializes
system files
Verifies the integrity
of the root filesystem
How many primary modes of
system operation are there?
1.
Login procedures that are
accomplished by dialing into
an access server are known
by which of the following
terms?
1.
2.
3.
4.
What is the function of the
kernel?
1.
Which of the following types
of cables is NOT used for
communications?
1.
2.
3.
4.
1-3.
1-5.
End of the day
End of the week
Normal conditions
Emergency conditions
1-9.
Which of the following is
NOT a reason why you should
monitor the network?
1.
2.
3.
4.
1-10.
3.
4.
2.
3.
4.
1-14.
Check system throughput
Monitor system
degradation
Monitor system security
Verify password attempts
1-15.
1-16.
2
Electrical
Logical
Parallel
Transfer
Which of the following terms
is used to describe the
process used by an
application to test a remote
device?
1.
2.
3.
4.
14
16
18
20
Administration
Hardware
Software
Both 2 and 3 above
Besides a physical interface
between the device and the
computer, what other type of
interface does a port
provide?
1.
2.
3.
4.
Which files were
accessed
When files were accessed
Who accesed certain
files
Each of the above
DIP switches
Expansion slot
Type of cable used
Order in which device
was installed
Network performance is
governed by which of the
following areas?
1.
2.
3.
4.
How many interrupt request
lines (IRQs) are there in a
PC environment?
1.
2.
3.
4.
IRQ values for a device may
be set through software or
manually by which of the
following ways?
1.
2.
3.
4.
By using the audit logs, a
network administrator can
track which of the following
areas?
1.
1-12.
To enable you to tune
your network
To establish
communications
To maintain a
performance history
To provide a statistical
basis for equipment
purchases
The main importance of
reviewing audit/event logs
is which of the following
functions?
1.
2.
1-11.
1-13.
Pinging
Ringing
Signaling
Sounding
1-17.
The interface between the
telecommunications access
software and the application
programs is known by which
of the following terms?
1.
2.
3.
4.
1-18.
2.
3.
4.
Communications
Utility
Network access
Network operating
1-22.
1-23.
Data integrity
Data validity
System access
System security
Private
Public
Shared
Each of the above
3
True
False
How many methods are used to
provide service restoration
after system degradation?
1.
2.
3.
4.
1-24.
Access to the file while
it is being worked on
Logging onto more than
one workstation at a
time
Security violations from
occurring
Unauthorized users from
logging onto the network
Once the software is
installed on the network, it
must be tested.
1.
2.
The different levels of
access can be designated by
which of the following
terms?
1.
2.
3.
4.
Network software often
provides some type of
locking capability. This
locking feature prevents
which of the following
actions?
1.
Which of the following terms
describes the prevention of
files from being updated by
more than one user at a
time?
1.
2.
3.
4.
1-20.
Network operating system
Network system software
Telecommunications
access software
Teleprocessing monitor
Electronic mail is
classified as what type of
software program?
1.
2.
3.
4.
1-19.
1-21.
Five
Two
Three
Four
DELETED
1-25.
1.
2.
3.
4.
1-26.
10
15
20
25
1-31.
Five
Six
Three
Four
1-32.
Bus
Ring
Star
Distributed
Which of the following
topologies permits
centralized diagnostics of
all functions?
1.
2.
3.
4.
1-29.
2.
3.
4.
Bus
Ring
Star
Distributed
1-33.
Which of the following
topologies is used in many
low-cost LANs?
1.
2.
3.
4.
4
Asynchronous data
control
Binary synchronous
communications
Synchronous data link
control
Both 2 and 3 above
The access method that will
be used is governed
primarily by which of the
following factors?
1.
2.
3.
4.
Bus
Ring
Star
Distributed
Bus
Ring
Star
Distributed
Which of the following
protocols is/are used-to
control line discipline?
1.
1-28.
Bus
Ring
Star
Distributed
Which of the following
topologies can be easily
adapted to the physical
arrangement of the facility
site?
1.
2.
3.
4.
Which of the following
topologies was the earliest
type?
1.
2.
3.
4.
Which of the following
topologies normally requires
the entire network be
brought down to add a new
node?
1.
2.
3.
4.
How many major types of LAN
configurations are there?
1.
2.
3.
4.
1-27.
1-30.
What is the minimum
percentage to be used in
calculating the available
resources for the network?
Protocol
Topology
Both 1 and 2
Network operating system
1-34.
Using the token passing
access method, what, if
anything, happens when the
transmitting station
receives the same token?
1.
2.
3.
4.
1-35.
1-38.
1.
2.
3.
4.
The message is being
sent
The message has been
passed around the
network
The message has been
appended by another
station
Nothing
1-39.
1-40.
1-36.
The physical layer is which
layer number of-the OSI
reference model?
1.
2.
3.
4.
1-37.
Five
Six
Seven
Eight
1-41.
Which layer provides
error-free transmission of
information over the
physical medium?
1.
2.
3.
4.
1-42.
Network
Presentation
Session
Transport
Which layer formats data to
be presented to the
application layer?
1.
2.
3.
4.
5
Network
Presentation
Session
Transport
Which layer performs the
functions that enable two
applications to communicate
across the network?
1.
2.
3.
4.
Data link
Network
Physical
Transport
Five
Two
Three
Four
Which layer ensures data
units are delivered
error-free, in sequence,
with no losses or
duplications?
1.
2.
3.
4.
One
Two
Three
Four
One
Two
Three
Four
The transport layer is which
layer number of the OSI
reference model?
1.
2.
3.
4.
How many layers are there in
the OSI reference model?
1.
2.
3.
4.
The network layer is which
layer number of the OSI
reference model?
Network
Presentation
Session
Transport
1-43.
Which layer represents the
services that directly
support users?
1.
2.
3.
4.
1-44.
Coaxial cable is used
extensively in LANs whenever
the distance involved is
relatively short, generally
less than how many miles (a)
for baseband and (b) for
broadband?
1.
2.
3.
4.
Coaxial
Fiber optic
Solid core
Twisted-pair
(a)
(a)
(a)
(a)
1
2
2
5
(b)
(b)
(b)
(b)
5
5
10
10
1-48.
DELETED
1-49.
Why is fiber optic cable
immune to electrical
interference of any kind?
For network purposes, 22and 24-gauge wire are the
most common types of which
of the following types of
cables?
1.
2.
3.
4.
1-46.
Application
Network
Physical
Session
Which of the following cable
types is the least
expensive?
1.
2.
3.
4.
1-45.
1-47.
Coaxial
Fiber optic
Solid core
Twisted-pair
1.
Which of the following types
of cable can handle a data
flow of up to approximately
one Mbps?
1.
2.
3.
4.
2.
3.
4.
Coaxial
Fiber optic
Solid core
Twisted-pair
1-50.
6
Has only one strand per
cable
Has thick shielding
Carries no electrical
current
Uses double insulation
on each wire
DELETED
1-51.
Firewalls can be divided
into how many different
categories?
1.
2.
3.
4.
1-52.
1-53.
1.
2.
3.
4.
Five
Two
Three
Four
What piece of hardware is
typically used to implement
packet filtering?
1.
2.
3.
4.
Which of the following
features can be provided by
a firewall?
Bridge
Gateway
Hub
Router
7
Address translation
Authentication
Virtual private networks
All of the above
ASSIGNMENT 2
Textbook Assignment: “LAN Hardware,” chapter 2, pages 2-1 through 2-10;
“Network Troubleshooting,” chapter 3, pages 3-1
through 3-7.
2-1.
Which of the following
devices is used to amplify
electrical signals carried
by the network?
1.
2.
3.
4.
2-2.
2-5.
Which of the following
devices serves as a
termination point for a
cable running from
individual nodes in a
network?
1.
2.
3.
4.
2-7.
Bridge
Gateway
Repeater
Router
Bridge
Gateway
Repeater
Router
2-8.
1.
2.
3.
1.
2.
3.
4.
4.
2-9.
Which of the following
devices works at layer seven
of the OSI model?
1.
2.
3.
4.
8
Architecture only
Cable only
Both architecture and
cable
Environment
Which of the following
cables is the best choice if
a secure network is needed?
1.
2.
3.
4.
Bridge
Gateway
Repeater
Router
Bridge
Concentrator
Gateway
Hub
Which of the following
factors need to be decided
on before determining the
type of connector to use?
Which of the following
devices works at the third
layer of the OSI model?
Bridge
Gateway
Repeater
Router
Bridge
Concentrator
Gateway
Hub
Which of the following
devices is a box with a
number of connectors to
which multiple nodes are
attached?
1.
2.
3.
4.
Which of the following
devices handles the first
two layers of the OSI model?
1.
2.
3.
4.
2-4.
Bridge
Gateway
Repeater
Router
Which of the following
devices is used to connect
identical network segments?
1.
2.
3.
4.
2-3.
2-6.
Coaxial
Fiber optic
Solid core
Twisted-pair
2-10.
Which of the following
cables is identified by a
designation number of RG-11?
1.
2.
3.
4.
2-16.
1.
2.
3.
4.
Coaxial
Fiber optic
Solid core
Twisted-pair
2-12.
Fiber optic connectors
differ from other connectors
in which of the following
ways?
1.
2.
3.
4.
1.
2.
3
4.
2-18.
Barrel
Elbow
RJ
T
2.
3.
4.
2-19.
Barrel
Elbow
RJ
T
2-20.
1.
2.
3.
4.
2-15.
200
500
800
1000
1.
2.
3.
4.
200
500
800
1000
2-21.
Calibrator
Conditioner
Scanner
Voltmeter
What term refers to the
cable that forms the main
trunk of a network?
1.
2.
3.
4.
9
Armature
Calibrator
Conditioner
Voltmeter
Which of the following
pieces of test equipment
should be used to check for
faults in a cable?
1.
2.
3.
4.
An SC connector is rated for
what number of matings?
Before they are
installed
During the installation
After they are installed
When things go wrong
To test electrical activity,
you will need which of the
following pieces of test
equipment?
1.
2.
3.
4.
An ST connector is rated for
what number of matings?
Size of the ferrule
Keyed connector
The number of matings
All of the above
Components should be tested
at all but which of the
following times?
1.
What type of connector is
used to connect telephones
to the wall?
1.
2.
3.
4.
2-14.
Data
Digital
Video
Voice
What type of connector is
used to link two segments of
cable in a straight run?
1.
2.
3.
4.
2-13.
200
500
800
1000
Which of the following
signals is NOT supported by
a broadband system?
2-17.
2-11.
An SMA connector is rated
for what number of matings?
Backbone
Main link
Node drop
Primary run
2-22.
What type of cable is a
100-ohm, multipair cable
used for voice grade
communications?
1.
2.
3.
4.
2-23.
2-26.
2-28.
One
Two
Three
Four
2-29.
Backbone
Main link
Node drop
Primary run
Network
Network
Network
Network
4.
3.
4.
Which of the following
equipment is used to attach
cable sections to each
other?
1.
2.
3.
4.
2-31.
Concentrators
Repeaters
Terminators
Transceivers
Cabling failures
Operating system
failures
Power outages
User actions
To determine the problem,
which of the following
information should be
gathered?
1.
2.
3.
4.
10
Breakout box
Datascope
Time domain
reflectometer
Voltmeter
Which of the following areas
cause the majority of all
network-related problems?
1.
2.
access card
interface card
operations card
union card
Commware
Hardware
Peopleware
Software
Which of the following is
NOT a specialized diagnostic
tool?
1.
2.
3.
2-30.
Concentrators
Repeaters
Terminators
Transceivers
Which of the following is
NOT a category of network
problems?
1.
2.
3.
4.
What device mediates between
the computer and the network
by doing the necessary
processing and translation
to enable users to send or
receive commands and data
over the network?
1.
2.
3.
4.
Which of the following
equipment is used to absorb
a transmission at the end of
a network?
1.
2.
3.
4.
What cable manages the bulk
of the traffic on a network?
1.
2.
3.
4.
2-25.
Coaxial
Fiber optic
STP
UTP
How many types of backbone
cable are there?
1.
2.
3.
4.
2-24.
2-27.
Nature of the problem
Node identification
number
User’s name
All of the above
2-32.
How many primary culprits
are there to network
malfunctions?
1.
2.
3.
4.
2-33.
2-37.
Five
Two
Three
Four
1.
2.
Component failures are
categorized into which of
the following types of
faults?
3.
4.
2-38.
1.
2.
3.
4.
2-34.
2-35.
Boot test
Pre-startup test
Power-on self test
Start test
2-39.
4.
2-40.
When a network malfunction
is detected, the alarm is
sent to which of the
following persons?
1.
2.
3.
4.
11
CSMA/CA
CSMA/CB
CSMA/CD
CSMA/CE
In a CSMA/CA system, the
media-access method uses
which of the following
signals before sending a
frame onto the network?
1.
2.
3.
4.
Department head
Network supervisor
Security officer
User
Collision
Derail
Jam
Wreck
When a node needs to send
data, it waits until the
line is quiet and then
transmits. This protocol is
known by what term?
1.
2.
3.
4.
Line conditioner
Network analyzer
Time domain
reflectometer
Voltmeter
Run the system
distribution
Run the system
initialization command
Shutdown and reboot the
system
Verify the domain name
Which of the following terms
is used to describe what
occurs when two nodes start
transmitting at the same
time?
1.
2.
3.
4.
Which of the following
pieces of test equipment is
the best tool to use for
network malfunctions?
1.
2.
3.
2-36.
Hard and soft
Hard and permanent
Soft and temporary
Permanent and temporary
PC tests are stored in ROM,
are known by which of
following
terms?
1.
2.
3.
4.
To reestablish services,
which of the following steps
is the first and easiest to
try?
NTS
RTS
WTS
WTS
and
and
and
and
CTS
CTS
NTS
RTS
2-41.
Which of the following terms
is described as a hardware
signal sent from a potential
transmitter to a destination
to indicate that the
transmitter wishes to begin
a transmission?
1.
2.
3.
4.
2-42.
2-44.
BTS
NTS
RTS
WTS
2-47.
True
False
2-48.
Five
Two
Three
Four
2-49.
1.
2.
3.
4.
2-45.
Blocktalk
Crosstalk
Impulse
White
1.
2.
3.
4.
2-50.
NER
NNR
SER
SNR
Crosstalk
Impedance
Attenuation
Degradation
How many types of line
conditioning are available?
1.
2.
3.
4.
12
Front-end crosstalk
Inter-end crosstalk
Mid-to-end crosstalk
Near-end crosstalk
Which of the followinq terms
is a measure of electrical
resistance?
1.
2.
3.
4.
Which of the following
ratios is used to determine
how long a cable segment can
be before the signal loss is
unacceptably high?
Crosstalk
Impedance
Attenuation
Degradation
A commonly used measure of
interference in twisted-pair
cable is referred to by
which of the following
names?
1.
2.
3.
4.
Which of the following terms
is not a form of noise?
Baseband
Broadband
Passband
Preband
Which of the following terms
is used to describe the
decrease in signal strength
measured in decibels per 100
feet?
1.
2.
3.
4.
Communication line problems
fall into how many different
categories?
1.
2.
3.
4.
Filters applied early in the
transmission are known by
which of the following
terms?
1.
2.
3.
4.
Whether the cable is
pre-made or you make it, it
should always be tested
before it is installed.
1.
2.
2-43.
2-46.
Five
Two
Three
Four
2-51.
Which of the following
equipment is used to extend
the transmission range
between devices that are
connected directly to each
other?
1.
2.
3.
4.
Line conditioner
Line driver
Network analyzer
Time domain
reflectometer
13

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