Ethernet cross-over cable

Concepts and Descriptions
This chapter provides technical explanations of many of the features of the Cisco 700 series
router. Although this information is not required to successfully install the router, it might
be of interest and assist with troubleshooting efforts.
Definition of Terms and Acronyms
This section defines some networking terms you will encounter when gathering required
information and using Cisco 700 series router manuals to configure the router.
Access code
A number that must be dialed preceding the telephone number to dial outside of a
specific telephone system, such as a Centrex system.
AT commands
ATtention commands (used for modem communications)
British Telecom
Challenge Handshake Authentication Protocol (CHAP)
A form of PPP authentication that requires an exchange of user names and secrets
(encrypted passwords) between two devices. This security feature is supported on lines
using PPP encapsulation. CHAP passwords are called secrets because they are sent
encrypted. Both devices must support PPP.
Concepts and Descriptions 6-1
Definition of Terms and Acronyms
Directory numbers
The equivalent of telephone numbers. This is the number the router dials to connect to
a remote router. ISDN BRI lines are generally assigned two local directory numbers,
one for each B channel.
Electronic Point of Sale
Information Element of a Q.931 message
Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI)
A digital communication medium that operates over existing analog telephone lines.
The BRI provides two 64-kbps B channels (for voice and data) and one 16-kbps D
channel (for customer and call information). This channel combination is sometimes
denoted as 2B+D.
Internet Protocol (IP) address
A network address that uniquely identifies a device on an IP network. This type of
address consists of 4 bytes, represented as decimal values, separated by periods, as in
Media Access Control (MAC) address
Also known as a hardware address. This address is assigned by the device manufacturer,
for example, 1234.5678.9000.
Point-to-Point Protocol (PPP)
A direct connection between two nodes; a connection without any intervening nodes or
switches. In an internetwork, the term refers to a direct connection between two
Password Authentication Protocol (PAP)
A form of PPP authentication that requires an exchange of user names and clear-text
passwords between two devices. PAP passwords are sent unencrypted. Both devices
must support PPP.
Port Address Translation
Cisco 700 Series Router Installation Guide
Public Switched Telephone Network
Routing Information Protocol
Service Profile Identifiers (SPIDs)
Numbers assigned by the ISDN service provider that identify the ISDN B channels.
They are assigned only in North America. The SPID format is generally the ISDN
telephone number with several numbers added to it. Depending on the switch type
supporting your ISDN BRI line, your ISDN line might be assigned none, one, or two
Transmission Control Protocol
Terminal Packet Assembler and Disassembler
ISDN Ports
Cisco 700 series routers provide one basic rate interface (BRI). The ISDN BRI service
provided by your telephone service provider offers two bearer channels (B channels) and
one data channel (D channel). The B channel operates at 64 kbps and carries user data. The
D channel operates at 16 kbps and carries control and signaling information, although it can
support user data transmission under certain circumstances.
Outside North America, telephone service providers typically provide an S/T interface. The
S/T interfaces are four-wire (two pairs of two wires) interfaces that supports full-duplex
data transfer over two pairs of wires.
Inside North America, telephone service providers typically provide a U interface. The
U interface is a two-wire (single pair) interface that supports full-duplex data transfer over
a single pair of wires.
Concepts and Descriptions 6-3
NT1 and the ISDN Ports
Commonly, telephone carriers use a four-wire network within their system. The wiring in
your home or business is a two-wire local loop. A Network Termination 1 (NT1) device
connects the telephone carrier four-wire network to a two-wire local loop.
Inside North America, it is common to find an NT1 built into a network device. Outside
North America, the telephone carrier or the user must provide an external NT1. To use the
internal NT1, the telephone carrier line is connected to an ISDN U port. If an external NT1
is required, the telephone carrier line is connected the ISDN U port on the NT1, and the
router’s ISDN S/T port is connected to the ISDN S/T port on the NT1.
The Ethernet ports on hubs are wired differently than the Ethernet ports on nodes. This
allows the devices to communicate with a straight-through Ethernet cable. Basically,
transmitted data must be sent from the transmit pin on one device to the receive pin on the
other device, and vice versa. Nodes connected to hubs handle this crossover internally. If
the signal does not cross over, the transmitted data is sent from the transmit pin on the
sending device to the transmit pin on the receiving device, and communications fails.
To connect two nodes or two hubs, the signal must be crossed externally. Usually this is
accomplished using an Ethernet crossover cable. The pins of a crossover cable have been
rewired so the transmit pins are connected to the receive pins, as shown in Figure 6-1.
Cisco 700 Series Router Installation Guide
Local applique
Opposite applique
RJ-45 pins
RJ-45 pins
Not used
Not used
Not used
Not used
Not used
Not used
Not used
Not used
Figure 6-1
Your Cisco 761,Cisco 762, Cisco 765, Cisco 771, Cisco 772, or Cisco 775 router can be
either a hub or a node. The HUB/NODE switch eliminates the need for a crossover cable.
When the switch is in NODE position, the router is seen as a node and connects to a hub
with a straight Ethernet cable. When the switch is in HUB position, the router can connect
to a network interface card (NIC) installed in a PC.
Cisco 766 and Cisco 776 routers have an unmanaged 4-port Ethernet hub. If you are
connecting a Cisco 766 or Cisco 776 router to another Ethernet hub, you must use a
crossover cable.
For additional information on standard cabling specifications, use the following paths:
On CCO use
On the Documentation CD-ROM use
Concepts and Descriptions 6-5
Cisco 700 Series Router Installation Guide