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University Microfilms International
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300 North Zeeb Road. Ann Arbor. Ml 48106-1346 USA
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Order Number 1SS5855
Analysis, design and performance evaluation of a video and
computer teleconference system for distance learning
Stubblebine, Stuaxt Gerald, M.S.
The University of Arizona, 1988
UMI
SOON.ZeebRd
Ann Aibor, MI48106
ANALYSIS, DESIGN AND PERFORMANCE EVALUATION OF
A VIDEO AND COMPUTER TELECONFERENCE SYSTEM
FOR DISTANCE LEARNING
by
Stuart Gerald Stubblebine
A Thesis Submitted to Faculty of the
DEPARTMENT OF ELECTRICAL AND COMPUTER ENGINEERING
In Partial Fulfillment of the Requirements
For the Degree of
MASTER OF SCIENCE
WITH A MAJOR IN ELECTRICAL ENGINEERING
In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9 8 S
STATEMENT BY AUTHOR
This thesis has been submitted in partial
fulfillment of requirements for an advanced degree at The
University of Arizona and is deposited in the University
Library to be made available to borrowers under the rules of
the Library.
Brief quotations from this thesis are allowable
without special permission, provided that accurate
acknowledgment of source is made. Requests for permission
for extended quotation from or reproduction of this
manuscript in whole or in part may be granted by the head of
the major department or the Dean of the Graduate College
when in his or her judgment the proposed use of the material
is in the interests of scholarship. In all other instances,
however, permission must be obtained from the author.
SIGNED:
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
/ Ralph Martinez
Associate Professor ^
of Electrical Engineering
Date
ACKNOWLEDGEMENTS
The thoughtful criticisms, suggestions and guidance
from my professors have added greatly to this thesis.
particular
Martinez
William
I
for
wish
his
Sanders
to
thank
my thesis
guidance.
for
his
evaluation.
Dr.
Larry
suggestions,
and
Don
I
am
also
direction
Schooley
lozia
and
invaluable technical assistance.
iii
advisor
Dr.
indebted
In
Ralph
to
Dr.
in
the
performance
for
his
noteworthy
John
Gross
for
their
TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS
viii
LIST OF TABLES
x
ABSTRACT
xi
CHAPTER
1
INTRODUCTION
1.1
1.2
1
The Evolution of Teleconferencing ....
Teleconferencing and Educational
Television at University of Arizona . . .
4
1.2.1
6
Campus Facilities
1.2.1.1
1.2.1.2
1.2.2
Transmission Paths
1.2.2.1
1.2.2.2
1.2.2.3
1.3
1.4
2
Video Architecture
Audio Architecture
Tucson Broadcast
Fort Huachuca, Arizona Link.
National Technological
University
1.2.3 Remote Conference Centers
Motivation For Change
Thesis Objective
REQUIREMENTS ANALYSIS
2.1
2.2
1
8
9
9
9
11
12
13
14
15
16
Lecture Reception
16
2.1.1
2.1.2
2.1.3
17
18
20
Display
Interaction During Lecture ....
Course Material Reception
Lecture Delivery
21
2.2.1
2.2.2
21
22
Presentation
Course Material Distribution. ...
iv
V
TABLE OF CONTENTS —continued
2.3
3
22
2.3.1
2.3.2
2.3.3
23
24
26
Electronic Mail
Remote Use of Computing Resources .
Grading
ANALYSIS OF DESIGN APPROACHES
3.1
3.2
3.3
3.4
4
Course Support
Video Broadcast with Audio Conference . .
Video and Data Broadcast with Audio
Conference
Data and Audio Conference
Video, Data and Audio Conference Using
ISDN Technology
VIDEO AND DATA BROADCAST SYSTEM FUNCTIONAL
DESIGN
4.1
4.2
28
31
35
40
46
Overview
46
4.1.1
4.1.2
46
47
Design Choice
System Organization
Control Site
49
4.2.1
49
Conference Components
4.2.1.1
4.2.1.2
4.2.1.3
4.2.2
Audio
Video
Data
Transmission Components
4.2.2.1 Satellite
4.2.2.2 Microwave Radio
4.2.2.3 Television Broadcast (ITFS).
4.2.3 Conference Control Processes ...
4.2.3.1
4.2.3.2
4.2.3.3
4.3
27
Main Process
Presentation Software ...
Telecommunications Package .
51
53
53
55
55
56
60
63
64
67
68
Remote Site
70
4.3.1
4.3.2
71
74
Work Station Components
Work Station Processes
vi
TABLE OF CONTENTS —continued
4.3.3
Reception Components
4.3.3.1
4.3.3.2
4.3.3.2
4.4
Satellite
Microwave Radio
Television Reception (ITFS).
77
78
79
Lecture Generation Support Facility ...
79
4.4.1
4.4.2
80
80
Lecture and Class Note Generation .
Class Note Distribution
4.4.2.1
4.4.2.2
5
Bulletin Board System
Operation
Bulletin Board Choice
...
PERFORMANCE EVALUATION
5.1
5.2
5.3
5.4
5.4.1
92
Observed Data
File Sizes
Display Times
Transmission Protocol
Bit Error Rate
Transmission Rate
File Size
Display Time
92
93
96
97
Simulation Tests and Results
SUMMARY AND CONCLUSION
APPENDIX A:
.
Probability Distributions
Hypotheses Testing
5.5.1
5.5.2
5.5.3
5.5.4
5.5.5
6.1
6.1
6.2
84
84
85
85
91
5.4.2
5.4.3
5.5
82
83
Simulation Goals
Performance Variables
Model Development
Input Parameters
5.4.1.1
5.4.1.2
6
77
104
....
106
107
107
107
110
112
Summary
Cost Analysis
Future Work
112
114
114
SIMSCRIPT II.5 SOURCE PROGRAM FOR
SIMULATION
116
vii
TABLE OF CONTENTS —continued
APPENDIX B:
EQUIPMENT LIST AND APPROXIMATE COSTS ...
LIST OF REFERENCES
125
129
LIST OF ILLUSTRATIONS
Figure
Page
1.1
University of Arizona Microcampus
Components
7
1.2
Transmission to Remote Sites
10
3.1
Video Broadcast with Audio Conference
Approach
30
Video and Data Broadcast with Audio
Conference
33
3.3
Data and Audio Conference
38
3.4
ISDN Information Flow for Video, Data and
Audio Conferencing
43
3.2
4.1
System Components and Information Flow ... 48
4.2
Control Site Conference Components
50
4.3
Signal Channel Spectrum
57
4.4
Control Site
Components
58
4.5
Satellite Transmission
Control Site Microwave Transmission
Components
61
4.6
Overview of Control Site Software
65
4.7
Control Site Telecommunications Package
Flow Chart
69
4.8
Long Haul Remote Site Components
72
4.9
Local Remote Site Components
73
4.10
Overview of Reception Processes
76
4.11
Lecture Generation Support Facility
81
5.1
System Diagram
87
viii
ix
LIST OF ILLUSTRATIONS —continued
Figure
Page
5.2
SIMSCRIPT Processes
90
5.3
Histogram of Observed File Sizes
94
5.4
Histogram of Observed Display Times
95
5.5
Density/Histogram Over Plot for File
Sizes
103
Density/Histogram Over Plot for Display
Times
103
BER Threshold for Incorrectly Displayed
Files
108
BER Threshold for Files Requiring
Retransmissions
109
System Performance Due to a Shift in
File Sizes
Ill
5.6
5.7
5.8
5.9
LIST OF TABLES
Table
Paae
5.1
Observed Sample File Size Statistics
....
94
5.2
Observed Sample Display Time Statistics . . .
95
5.3
Model Parameters for File Size
98
5.4
Model Parameters for Display Time
99
5.5
Hypotheses Test Comparison for File Size
. . .
101
5.6
Hypotheses Test Comparison for Display Time . .
102
X
ABSTRACT
Video teleconferencing is a successful tool in the
education and business industry because of its ability to
reach a large audience at numerous remote locations.
New
computer and communications technology allows for advances
in
teleconferencing
analysis
of
performed
educational
to
develop
design approaches.
various
capabilities.
In
teleconferencing
viable
educational
this
thesis,
an
requirements
is
teleconferencing
These design approaches must consider
transmission
means
and
typical
methods
of
instruction.
One design
design
is
performed.
performance
language.
approach is selected
models
and
The
design
the
is
Simscript
and
a functional
evaluated
II.5
using
simulation
Curve fitting techniques are applied to observed
data to create probability distribution functions used in
creating an accurate model.
The performance evaluation is
used to optimize the transmission protocol and validate the
design.
The simulation results show that with a 9600 baud
transmission
rate,
the
effects
of
degraded
transmission
lines, short display times or abnormally large file sizes,
have no significant effects on the proper perfoinnance of the
system.
xi
CHAPTER
1
INTRODUCTION
Teleconferencing
denotes
the
technique
whereby
a
group of geographically dispersed people can hold meetings
and discussions via an intervening video, voice, and data
communications medium.
1.1
Evolution of Teleconferencing
Educators were the first to employ teleconferencing
concepts
courses
on
a
significant
scale.
available to students
audio conferencing techniques.
Teleconferencing
in distant
made
locations using
By the mid 1960's to 1970's
large scale audio conferencing systems, some linking up to
200 locations were dominant [5].
popular
because
of
its
Audio conferencing became
flexibility
in
linking
sites.
Technological
advances
eventually
gradual
replacement
of
large
the
multiple
resulted
antiquated
in
a
audio
conferencing systems.
In 1927 Bell Laboratories carried out experiments in
transmitting pictures.
but
it
was
not
A prototype system emerged in 1956,
until
1970
that
AT&T
produced
the
Picturephone Meeting Service which allowed service customers
to
hold
meetings
at
specially
around the country [5].
equipped
studios,
located
However, this system was not used
1
2
to a significant degree either.
a
major
boost
with
the
Video conferencing received
growth
of
satellite
broadcast
television from which special event conferencing started to
emerge.
The application of digital technology to slow-scan
video, and
appeared
about
the introduction of the electronic
in the middle 1970's.
'meet-me'
bridges
for
blackboard
The late 1970's
dial-in
audio
brought
conferencing.
'Meet-me' bridging allows conferees to independently call in
and
join
the
conference,
thus
eliminating
the
need
for
performing an extended call set-up procedure at some central
location prior to the conference.
Digital transmission and
microprocessor technology encouraged the investigation and
development
of
advanced
signal
compression
techniques
permitting the compression of speech and video images into
smaller bandwidthsThe
1980's
teleconferencing.
to
materialize
may
be
termed the digital decade
for
It was at this time that concepts began
in
technology
components.
Digital
transmission and digital bridges resulted in improved voice
quality.
The first video codecs entered the marketplace,
enabling wide band video signals to be compressed into 1.5
or 2 Mega bits per second (Mbps) digital channels.
The
codec takes the analog signals representing the picture,
converts them to digital form, and effects the compression,
before transmitting the digital signals to the distant site.
3
A
inverse
Similar
process
takes
technological
Computer
graphics,
place
at
advances
facsimile
the
have
remote
also
scanners
location.
resulted
and
in
electronic
tablets.
Much
Definition
now
Television,
international
[12],
research
High
studio
or
Definition
characterized
by
an
vertical
resolution
systems.
It also has
focuses
or
HDTV.
production
Television
improvement
of
on
the
area
Proposed
standard
(HDTV)
in
approximately
of
both
in
is
High
as
May
1986
television
horizontal
2:1
an
over
and
existing
greatly improved color rendition due
to component signals, a wide aspect ratio of at least 5:3
and stereophonic digital audio.
The worldwide pioneer in HDTV for many years
been NHK, the Japan Broadcasting Corp., Tokyo.
has
NHK's studio
production standard calls for 1125 scanning lines per frame,
60 fields per second, 2:1 interlaced scanning, and a 16:9
aspect ratio.
The aspect ratio is the ratio of frame width
to frame height as defined by the active picture.
Also,
interlaced scanning is a process in which the distance from
center to center of successively scanned lines is two or
more times the nominal line width. The adjacent lines belong
to different fields.
one
frame,
one field
For instance, when two fields make up
is
formed
by scanning
all the odd
lines, the other by scanning all the even lines.
The 1125
4
lines
were
chosen
to
obtain
an
approximate
doubling
of
vertical resolution and to allow for a 9/5 and 15/7 down
conversion to Europe's 625-line standard and the National
Television System Committee's(NTSC) 525-line standard.
Teleconferencing is not new in the United States.
However, the growth of teleconferencing, with the exception
of audio conferencing, has not matched earlier expectations.
Nevertheless, a new age has come where the lessons of the
past
are
now
transform
combining
with major technical advances to
teleconferencing
into
a
effective communications tool.
practical
and
cost-
The new video, audio and
computer technologies must be incorporated into the existing
teleconferencing systems at
University of Arizona
for an
improved distant or remote learning capability.
1.2
Teleconferencing and Educational Television
at University of Arizona
Within
the
Department
of
Educational
Telecommunications at -t.he University of Arizona there is an
instructional television unit called Microcampus.
The word
"Microcampus" was coined by Dr. Walter J. Fahey, Dean of the
College of Engineering at the University of Arizona, 19691977.
He
had
the
foresight
Educational Delivery System.
part,
made
possible
in
to
envision a
new type of
This delivery system was, in
early
1972
by
developments
in
5
videotape recorder technology.
The Microcampus concept is to bring the classroom to
the
students
no
matter
where
they
are.
It
initially
consisted of a single classroom modified for the videotaping
of lectures.
campus
Video cassettes were mailed to students at off
locations.
The
Microcampus
system
has
been
in
operation since February, 1972, at which time the tapes were
black and white.
In August, 1973, a second classroom was
modified for the videotaping of lectures.
In
1978,
scan video.
some experimentation was done with slow
Slow scan video allowed transmission of video
images over a normal telephone line-
At that time each
frame took about 35 seconds to transmit.
Although a step
forward, the slow scan video approach was not satisfactory
for online broadcast of classes.
In
1979, a new approach for Microcampus outreach
project was tried.
audio
was
The project was abandoned.
televised
The black and white program video and
using
Instructional
Television
Fixed
Service, or ITFS, transmitters on channels H2 and H3 (2665
MHz and 2677 MHz respectively).
and
now
Tucson
Allied-Signal
locations,
Aerospace
IBM,
Company,
The project was a success
Hughes,
Burr-Brown
can watch their
and
classes
live.
In the early 1980's, construction was completed for
a full color production facility at its present location in
6
the
Harvill
building
Additionally,
a
at
the University of
microwave
transmission
Arizona (UA).
link
to
Fort
Huachuca, Arizona was added.
In 1984, a satellite connection was established to
the National Technological University (NTU).
The University
of Arizona can now televise their classes nationwide through
the NTU satellite system.
advanced
educational
NTU's mission is to serve the
needs
of
graduate
engineers
and
technical professionals as well as award, degrees at the
master's level.
offerings
from
Its consortium currently consists of course
31 universities
across the
United States.
Students, mostly corporation sponsored professionals, sign
up for the classes in hundreds of different receive sites.
In
June
1987,
NTU
graduated
its
first
set
of
Master's
students.
While 1985 brought the expansion of Microcampus to
an
additional
production room,
the last
major change in
transmission facilities occurred in August 1988, when the
Instructional
Television
Fixed
Service
(ITFS)
moved
its
point of origin from the UA campus to the FM Engineering
site in the Tucson mountains, on the west side of the city.
1.2.1
Campus Facilities
The University of Arizona Microcampus components are
shown in Figure 1.1.
7
MICROWAVE
FACILITIES
SATELLITE
TERMINAL
ITFS
TELEVISION
FACILITIES
VIDEO
PRODUCTION
ROOM
*1
TELEPHONE
SWITCH
CONTROL
ROOM
VIDEO
PRODUCTION
ROOM
*2
ADMINISTRATION
ENGINEERING
SUPPORT
L BRARy
Figure 1.1 - University of Arizona Microcampus Components
8
1.2.1.1
Video Architecture.
The particular portion
of Microcampus that we are concerned with in this section
consists of two video production rooms and a control room.
These
facilities create
the
NTSC color video signal
for
transmission to the remote sites.
One classroom contains four cameras, while the other
has three.
In both rooms, there are two cameras on either
side, at the back of the room, and one camera directly over
the instructor's desk.
The camera over the instructor is
used to display the course material.
One production room
has an additional camera at the front of the room to display
the student audience.
The video signals for a particular room are routed
to the control
room
Control Unit (CCU).
where they
interface
with
a
Camera
The CCU's primairy function is to form a
composite video signal. The video signal is then tied into
the Special Effects Generator (SEG).
The SEG provides the
control room operator with a variety of options to modify
the video signal before it becomes the final product.
features include
mixing, switching or keying video sources
to the program line output.
cameras,
SEG
computer
generated
Various inputs exist including
text,
VCR's,
and
character
generators.
After the
output
is
sent
signal
to
the
is
manipulated by the SEG, the
routing
switcher.
The
routing
9
switcher permits the signal to be routed to an assortment of
transmission media discussed in Section 1.2.2 Transmission
Paths.
1.2.1.2
component
incoming
of
Audio
the
Architecture.
Microcampus
telephone
lines
and
provides
one
The
audio
for
bridging
dedicated
return
audio
two
line.
These telephone lines allow remote site students to call in
during the lecture, or conference, and ask a question.
Each
video production classroom has microphones located in the
audience, at the presenter's desk and on the instructor's
body.
The microphones are mixed
with the incoming phone
lines and are fed out to the lecture room, VCRs, routing
switch and playback amplifiers.
adjusts
the
input
audio
The control room operator
volume
on
the
control
panel
according to location of the input source.
1.2.2
Transmission Paths
The
NTSC
switch
of
the
Tucson
sites,
video
signal
Microcampus
and
long
throughout the country.
is
sent
control
haul
room
sites
from
the
routing
to
local
remote
within
Arizona
Figure 1.2 provides a generalized
topology of the transmission paths.
1.2.2.1
and
Tucson Broadcast.
After leaving the
10
NTU
SATELLITE
niCROWAVE
MICROCAMPUS
LONG HUAL
REMOTE SITES
(FT. HUACHUCA.AZ)
ITFS
TELEVISION
LOCAL SITES
( TUCSON )
Figure 1.2 - Transmission to Remote Sites
11
routing switch in the control room, the video and audio is
sent to the microwave transmitters located on the roof of
the building.
The
Studio to Transmitter Link, or STL,
microwave radio has the capability of transmitting one video
6 MHz NTSC signal with two audio subcarrier channels.
microwave
signal
is
transmitted
at
120
milli-watts
The
at
a
distance of nine miles to the Tucson FM Engineering Site
located on the west side of Tucson.
There the signal is
received, demodulated, and the base band video and audio is
input
to
D1
and
D3
ITFS
retransmitted
utilizing
antenna.
is
It
Allied-Signal
an
received
Areospace
transmitters.
The
omni-directional
signal
is
transmitting
by IBM, Hughes, Burr-Brown and
Company,
by
means
of
parabolic
dishes pointed at the transmitters -
1.2.2.2
the routing
Ft. Huachuca, Arizona Link.
switcher the
video and
audio
separately to the microwave transmitter.
As they leave
signals travel
The transmitter is
located in a room approximately 50 feet from the control
room in the University of Arizona's Harvill building.
The
video and audio signals are split, each pair transmitted
onto two separate wideband channels on the Microwave Video
Radio, or MVR.
The microwave dish is located on top of the
Harvill building and
is aimed at the Mount Bigelow relay
station located Northeast of Tucson.
The transmit frequency
12
to Mount Bigelow is at 1730 MHz and 1760 MHz-
The shot is
sent to "TV Hill" in Sierra Vista, Arizona at 1810 MHz and
1840 MHz and again relayed to its final destination at the
education center on Fort Huachuca at 1730 MHz and 1760 MHz.
The signal is received, demodulated and split.
feeds
the television
monitor
in the classroom
One leg
while the
other is routed to a VCR for taping of the lecture.
1.2.2.3
satellite
based
National Technological University.
delivery
system
delivers course
The NTU
material
through the Ku-band on the GSTAR 1 satellite located at 103
degrees west longitude.
11,700
MHz to
12,200
The Ku-band occupies the spectrum
MHz.
NTU
broadcasts
simultaneously over one transponder.
two
channels
The equipment needed
at any site for receiving NTU transmissions includes a Kuband antenna, low noise amplifier or block down converter,
video/audio demodulator (receiver) and a splitter, if two
simultaneous
channels
are
desired.
The
University
of
Arizona has the capability of transmitting to the satellite
on either channel.
The vertically polarized uplink video
frequencies
are
follows:
channel
14,289
B:
as
MHz.
channel
There
are
A:
14,259
two
frequencies at 6.2 and 6.8 MHz. frequency.
audio
MHz
and
carrier
The receiver
band width is 22 MHz.
The Microcampus is linked from the routing switcher
13
to the NTU satellite system. The composite NTSC signal is
guided through a few band pass filters to the top of the
Harvill
building
where
the
modulation
and
transmission
equipment resides.
1.2.3
Remote Conference Centers
The Tucson remote conference centers receive their
video signal through the ITFS transmission system described
in Chapter 1.2.1.1 above.
The conference center consists of
a conference room with a television monitor and telephone.
These centers are located at IBM, Hughes, Burr-Brown, and
Allied-Signal Areospace Company.
The Fort Huachuca educational center has the Video
Microwave Radio on location.
The output of the wideband
video signal of the radio is split to the classroom and a
monitor/VCR taping location.
The conference room contains a
telephone for the audio feedback portion of the conference.
The
typical
NTU
remote
solely of a television monitor-
conference
room
consists
Until Fall 1988 no audio
feed back capability was provided for remote NTU sites.
Now
a speaker phone for use with NTU remote sites calls directly
to
the
professor's
desk
on
phone
#(602)621-3332.
equipment needed at any site for receiving
transmissions
includes
a
Ku-band
The
NTU satellite
antenna,
low
noise
amplifier or block down converter, video/audio demodulator
14
(receiver) and splitter if two simultaneous channels are
desired.
The
frequencies
are
horizontally
as
follows;
channel B: 11,987.5 MHz.
polarized
channel A;
Most
receive
11,960.5
Ku-band
video
MHz and
receivers
may
terminate two audio channels simultaneously.
1.3
Although
teleconferencing
several
Motivation For Change
Microcampus,
are
complaints
generally
have
arisen
NTU
and
educational
considered
regarding
successful,
the
existing
delivery of courses.
NTU queries the students who participate in their
teleconference educational courses [27].
Results of these
surveys indicate that the complaints of televiewers at NTU
sites are almost identical to those of the Microcampus at
the University of Arizona.
Some of the grievances from the
two groups are as follows;
a. Manual distribution of class material, such as
notes, homework, tests and graded work takes too
long.
b. Difficult to send completed homework and tests to
instructors.
c. Poor student/instructor interaction for remote
students.
d. Course material and charts not readable by TV.
e. Camera shows instructor when he talks about a
view graph; therefore, insufficient time to take
notes.
15
f. Poor resolution; therefore, difficult to read
notes.
g. Small and illegible writing on board.
h. Camera should spend more time on what the prof is
writing and less on prof.
The teleconferencing components at the NTU remote
sites are essentially identical to those components at the
Microcampus remotes.
1.4
Thesis Objective
The objective of this research is to functionally
design
an
architecture
teleconferencing
system
for
an
improved
for
distance
educational
learning.
A
requirements analysis will be performed using the University
of Arizona Microcampus as a model.
Several teleconferencing
approaches will be examined from which one approach will be
functionally designed and a performance evaluation of the
design will be conducted-
CHAPTER 2
REQUIREMENTS ANALYSIS
This
educational
chapter
outlines
teleconferencing
requirements
facility.
for
Monetary
an
and
technological constraints are not considered here but may be
barriers to the implementation of requirements in the later
design stage.
The requirements for an improved educational
teleconferencing facility at the University of Arizona are
based on information from a variety of sources.
Input was
primarily obtained from students that regularly attend oncampus Microcampus classes, remote site students. National
Technological University students, professors, and employees
of the teleconferencing facility.
2.1 Lecture Reception
Independent
reception
educational
is
the
of
most
the
lecture
important
teleconference.
This
media,
key
to
section
good
a
lecture
successful
addresses
the
reception of video or computer images, or a simultaneous
combination of both-
Also included in the lecture reception
section is the distribution of course material.
Course material consists of class notes and support
material.
Throughout this document, class notes will be
considered to be the hard copy documents produced by the
16
17
instructor and used by the student as a learning aid.
Class
notes may be a subset or the entire collection of slides
used by the instructor during the lecture.
Support material
refers to the hard copy documents other than class notes
which are provided to the students by the instructor.
These
can include reference articles, or reprints, homework, and
test material.
The
remainder
of
Section
2.1
describes
requirements for acceptable lecture reception.
requirements
display
of
are
categorized
course
in
presentation,
the
The primary
following
interaction
the
groups:
and
course
material reception.
2.1.1
Display
Independent
of
the
media
(i.e.
video,
computer
graphic) used during the conference, all displays must be
clear
and
legible.
Both
video
displays will be considered.
and
computer
conference
All forms of display must be
readable with little strain from the furthest point in the
local and remote conference rooms.
An unclear or unreadable
presentation of course material makes learning for students
difficult,
if
not
attributed
to
several
students
impossible.
indicates
factors.
that
poor
Inferior displays can
An
NTU
contrast
survey
between
of
be
its
course
material and the board, rapid camera switches between the
18
slides
and
the
instructor,
and
poor
video reception are
causes of problems [27].
The requirements for an improved display include the
following:
1. Display screens must be visible without strain
from the farthest point in the conference room.
2. The remote student needs the flexibility of
looking at the lecturer or the course material.
Thus, simultaneous display of course material and
the instructor is ideal.
2.1.2
Interaction During Lecture
Interaction between instructors and students during
the lecture must be improved for a more effective learning
environment.
Interaction is considered a major problem for
both
and
local
remote
teleconferencing
interaction
with
students
environment.
an
instructor
in
the
The
sole
a
remote
for
educational
source
of
Microcampus
student during a lecture is through the telephone linkage.
The
audio
students,
feedback
local
link
or
has limited
remote,
NTU/Microcampus environment.
ask
effectiveness.
questions
to the "fishbowl"
environment
educational video teleconferencing.
audio-shy.
the
Far fewer remote Microcampus
students ask questions during the lecture.
attributed
in
Few
This problem is
associated
with
Students are camera and
19
For the most part, NTU remote students are not given
the opportunity to participate through the audio conference,
because it is not a standard feature for NTU lectures.
outlined
in
the
existing
audio
architecture
As
Section
1.2.1.2, current capabilities for multiple remote student
audio
conferencing
with
the
University
severely limited to two outside calls.
feature
is
only
offered to
Fort
of
Arizona
are
In practice this
Huachuca
and
the
major
Tucson remote Microcampus subscribers.
State of the art computer Decision Support Systems
allow
a
computer
remote users.
send
"brain
anonymously.
conference
between
multiple
local
and
Some of these systems permit conferees to
storming"
solutions
to
other
conferees
Similarly, in the educational teleconferencing
environment, students should be able to send questions to an
instructor without being identified. Remember the old adage,
"The only dumb question is the one that is never asked."
An
on-line question feature provide remote students with the an
added edge of increased student-instructor interaction over
the
local
classroom
teleconferencing
student.
systems
may
The
future of
include
educational
Decision
Support
Systems as a vital component of the conference.
Interaction requirements include the following;
1. Additional interaction tools over and above the audio
link for Microcampus students.
20
2. A means of improving the interaction between the
local student and the instructor.
2.1.3
Course Material Reception
Reception
material
student.
is
of
both
especially
class
notes
important
and
to
other support
the
remote
site
The critical factors in satisfactory reception of
course material are the time lag or delay in reception,
clarity
and
delivery.
logistics,
Both
costs
as
well as costs associated
and
logistical
with
requirements
are
addressed in the Course Material Distribution Section 2.2.2.
Human factors often cause the time lags associated
with slow delivery of course material to remote sites.
The
instructor may forget to deliver course material through the
manual
distribution
facility.
As
a
consequence, course
material may not be available for delivery until the remote
student
queries
the
instructor.
Also,
instructors
may
prepare course materials at the last minute, in which case
the material is not available for delivery.
A lag of a few
days may be the result of the distribution system itself.
Today's teleconferencing systems require end-to-end
transfer of graphic course material which may need to be
printed as well as displayed.
have readable copies
of
Remote site students must
course material.
Such material
varies from instructor to instructor and lecture to lecture.
21
Most instructors prepare class notes from a transparency,
thus
printing
them
on standard
8
1/2
by 11 inch
paper.
These notes are prepared ahead of time or constructed during
the lecture as the instructor speaks.
Since lecture notes
often contain images of the subject material, a simple ASCII
text transfer of course material is insufficient for course
instruction methodology.
Therefore, an improved educational
teleconferencing system
has the following Course material
reception requirements:
1. Reduced time lag associated with the delivery of
course material.
2. Remote site user equipment that includes a printer
capable of creating graphics and textual course material.
2.2 Lecture Delivery
2.2.1
Presentation
An improved
system
should
instructors teaching methods.
must
not
be
trapped
behind
presenting his lecture.
not
interfere
with the
For example, the instructor
a
computer
terminal
when
The system should be flexible to
accommodate several professor's teaching styles and methods.
The
presentation
instance,
easy.
advancing
or
must
going
be
in
be made
easy.
user
back to
Also such tasks as drawing
lecture should
mostly
system
a
a
friendly.
slide
For
should
be
picture during the
These two scenarios occur
response to a question or to clarify a
point
22
further.
2.2.2
Course Material Distribution
Just as the slide presentation should be easy, the
course
note
distribution
should
be
hassle
free.
Human
manpower needed for course material distribution should be
minimized.
Ideally distribution costs should be reduced.
The requirements are:
1. Limit manpower necessary for course material
distribution.
2. Reduce course material distribution costs.
3. Automate the course material distribution system.
2.3
2.3.1
Course Support
Lecture Generation
Although every course does not use slides, course
notes are used to
supplement the course lecture and may
serve to relieve the students from having to rewrite every
slide
presented
typically
just
lectures.
It
slides
as
during
copies
is
the
of
lecture.
the
slides
Course
notes
presented
in
are
the
important that the instructor make the
interesting
as
possible
to
keep
the
students
of
computer
alert to the course material.
There
are
numerous
brands
and
types
generated slide creation and presentation software available
23
which allow a broad range of functions.
the
IBM
PC
Graphics.
are
Show
Partner,
Some available for
Storyboard,
and
Harvard
Software must be compared and selected based on
the desired features.
At a minimtun, the selected software
must be interesting and easy to use.
Requirements:
1. Creation of a slide or story should be uncomplicated and
easy to learn.
2. Conversion of class notes to the new version should be
easy.
3- Creation of a slide and lecture using computer tools must
not require a substantial amount of time.
4. Once created, slides should be easy to modify to include
new material.
2.3.2
Electronic Mail
A
recent
article
concludes
that
while
students
prefer electronic mail to supplement their interaction with
faculty, it also saves faculty time and department resources
[19].
Electronic mail is a common network service.
A user
composes a message on a local computer; supplies the address
of
the
recipient's
mailbox,
which
may
be
on
a
remote
computer; and instructs the local mail systems to send the
message to the indicated recipient.
The local mail system
assumes responsibility for the message.
via
the
network
to
the
destination
appears in the recipient's mailbox.
The message is sent
host
and
eventually
The flow of information
24
within an educational institution is instructor to student,
student to instructor, and student to student communication.
The electronic mail facility may bridge the information gaps
outside of the class.
The instructor sends mostly course information to
the students.
These electronic mail messages may be the
class syllabus, homework assignments, take home tests or
class
announcements.
It
is
also
possible
that
graded
homework and tests, or just the results, may be sent to the
students.
Students communicate to both the instructor and to
each other.
completed
Messages to the instructor are likely to be
homework assignments.
Homework assignments may
consist of text files or large computer programs.
Students
may also send messages to the instructor for clarification
of assignments or the lecture.
other
students
Students send messages to
for coordination of
assignments and group
projects.
2.3.3
Remote Use of Computing Resources
The university environment typically has extensive
computing facilities which, among other uses, provide class
support.
The
computing
programming
in
application
programs.
higher
facilities
level
There
languages
are
two
may
be
used
or simply
ways
to
for
running
provide
25
computing resources to studentsremote
login
modems
and
necessary
provides
access
communication
computing
Remote students access or
to these resources through
lines.
resources
may
be
Alternatively,
the
duplicated
the
at
remote site.
Access to remote facilities is commonly performed
via
computer
networking.
Mainframes
are
often
linked
together through dedicated communication lines, such as 9600
baud,
which
services .
provide
remote
This
method
login
and
results
electronic
in
some
mail
added
telecommunication costs, but little duplication of hardware.
The
benefits
of
computer
networking
include:
increased
opportunity for collaboration with colleagues, computer and
information resource sharing, rapid dissemination of reports
and
information,
easy
access
to
data
and
information,
development of special interest groups and development of
specialized services [19].
Duplication of computing facilities may include down
loading application software running on a mainframe or PC to
a
personal
computer
(PC)
at
the
remote
application programs executing on VAXs at
have sister versions which run on PCs.
site.
Some
the university
Such an application
program, like NETWORK 11.5 or HPSIM, may be stored on a
university
execution.
mainframe
for
down-loading
to
remote
PCs
for
Compatible code is developed by students which
26
may
run
in
either
the
PC
or
mainframe
environment.
Similarly, PC software might used at the university may be
provided to other remote PCs for execution via a bulletin
bocircl sys tein.
2.3.3
Grading
A fully integrated system may have the capability of
computer graded tests or
homework.
Computerized grading
depends heavily upon having a machine readable source.
It
may be impractical to limit students to using mark-sense
type forms for computer input.
Much research is necessary
in handwriting recognition and interpretation, as well as
other aspects of the Artificial Intelligence (AI) field of
"intelligent" grading.
Computer programs which administer
homework and test material could also be used to grade and
tabulate the student response.
CHAPTER 3
ANALYSIS OF DESIGN APPROACHES
Approaches to teleconferencing vary substantially as
do the types of media and technology that are used.
important objective of
A
simple
design
is
communication faults.
the design approach is simplicity.
less
likely
to
have
system
important
to
and
It is useful to keep in mind state of
the art as well as future technological advances.
also
An
note
the
capabilities
of
each
It is
design
approach with its unique features.
The design approaches in this chapter are labeled
according to their featured media and mode of transmission.
The media options include video, audio, and data.
Data
transfers may contain files or messages controlling remote
processes.
conference.
Two communication mode options are broadcast and
In this chapter, broadcast is regarded as a one
to many simplex transmission.
For a particular broadcast
media, remote users have no means of transmission to the
originating
end.
For
the
conference
mode,
using
a
particular media, communications can occur in full duplex or
half duplex.
That is, communication transfers occur in both
directions.
27
28
3.1
Video Broadcast with Audio Conference
The Video Broadcast with Audio Conference approach
is similar to the existing teleconferencing scheme, but it
also
provides
generated
the
added
graphics
into
feature
an
of
NTSC
converting
television
computer
signal
for
broadcast.
A test trial of this option was performed at the
University
of
Arizona
Summer of 1988.
3.1.1
Microcampus
facilities
during
the
ability
to
Test results were favorable.
Operational Description
This
design
approach
features
the
transmit computer generated video images in addition to the
features provided by the existing architecture outlined in
Chapter 1.
most
Currently, video based delivery is one of the
common
means
for
transmitting
educational
courses.
Course material is prepared in advance on paper and then
displayed in front of the camera by the instructor during
class.
Preparation of course material occurs at a Lecture
Generation
Support
Facility
described in Section 4.4.
(LGSF)
similar
to
the
one
As an example, the presentation
software IBM Storyboard Plus has a program called "PictureMaker" which allows users to generate picture files using an
electronic mouse, keyboard or RGB camera with a specialized
frame
grabber
[18].
Slides
are
prepared
and
then
put
29
together in a "story".
IBM's Story-Teller software allows
for an ordered arrangement of picture files.
Many special
effects may be used to create the story, resulting in a more
interesting presentation.
At
the
Story-Teller,
mouse.
source
start
of
advancing
a
lecture
slides
the
using
instructor
the
runs
keyboard
or
a
The video control room operator switches the input
between the computer
and
the
video
image
of
the
instructor.
3.1.2
Detailed Description
Figure
3.1
shows
the
components
of
broadcast with audio conference approach.
the
video
All components
are the same as those in the existing system except for the
additional
video
source
input
to
the
Special
Effects
Generator, RGB-NTSC encoder, PC to RGB level converter, and
work station.
IBM PCs generate graphic signals in a unique format
containing RGB and intensity bits.
picture
element
primary.
expression
one
bit
deep
per
color
That is, the picture element is either red or
black along the red axis.
axis, and
only
RGB bits result in a
Green or black on the green
blue or black on the blue axis.
If
you
add
another bit, intensity, then you have up to 15 different
colors compared to only 8 in the 3 bit case.
30
CONTROL
SITE
TRANSMISSION
FACILITY
AUDIO
VIDEO
( 6MHZ)
VIDEO
0-4.2 MHZ
VIDEO
PRODUCTION
EQUIPMENT
VIDEO
SWITCH
NTSC ]
ENCODER
COURSE NOTE
PRESENTATION
SOFTWARE
CCA GRAPHICS
AUDIO
MICROPHONE
TELEPHONE LINES
MIXER/
AMP
SPEAKER
Figure 3.1 - Video Broadcast with Audio Conference Approach
31
The raster scan standard of graphic output boards
such as the monochrome graphics card. Color Graphics Adaptor
(CGA), and Extended Graphics Adaptor (EGA) differs for each,
and is incompatible with television rasters.
An encoder is
necessary to convert the scan rate for both horizontal and
vertical
frequencies
to the
National
Television
Standard
Committee (NTSC) standard used in the United States.
The
CGA horizontal scan rate is just above 15 KHz whereas the
EGA
and
other
higher
resolution color
range up to the high 30 KHz.
graphic
standards
The encoder needed to convert
EGA to NTSC is approximately an order of 10 higher in cost
to that of a CGA encoder.
3.2
Video and Data Broadcast with Audio Conference
Despite
the
high
over
the
last
enjoyed
level
of
decade,
publicity that
the
growth
conferencing has failed to meet expectations.
it
of
has
video
A fundamental
reason for the slow rate of growth has been the scarcity and
high cost of the wideband transmission circuits required for
full-motion video.
full-motion
video,
capabilities
channel.
many
of
Our approach utilizes existing wideband
but
without
adds
graphics
requiring
The
approach
the
logistic
an
and
text
additional
image
wideband
described in this section solves
problems
distribution of course material.
associated
with
the
Though a brief operational
32
description of this approach is presented below, detailed
implementation is discussed in Chapter 4, Video and Data
Broadcast Systems Design.
3.2.1
Operational Description
The three major facilities in the teleconferencing
system consist of the Generation Support Facility or LGSF,
Control Site and Remote Sites (see Figure 3.2).
The LGSF is an independent facility used to support
the generation and distribution of course material.
lecture is prepared using graphic software.
A class
Once all the
notes are created, another application program is used to
arrange the slides in presentation order.
The
lecture
is
hand
carried
on
diskette
or
electronically sent to the Control Site via the university
broadband
network.
Non-ASCII
files
may
be
transferred
through the university broadband network (Sytek Local Net 20
and 2000) by use of communication protocols such as Kermit
[9].
Kermit
has a feature called 8 bit prefixing which
converts all non-printable characters to two byte printable
characters.
bit
Upon reception, the original non-printable 8
sequences
are
recreated.
This
feature is
necessary
because the communications network interprets certain eight
bit combinations
characters.
in the
graphic
file
as its own control
A test of this procedure was performed during
33
corrTROL
3ITE
TRANSMISSION
FILCILITV
LAPC-E
PROJECTION
SCREEN
VIDEO
C 6 MHZ )
DATA
Q
VIDEO f
0-4.2 MHZ
MOUSE
AUDIO
VIDEO
SWITCH
NTSC
ENCODER
COURSE NOTE
PRESENTATION
SOFTWARE
CGA GRAPHICS
SERIAL PORTS
MICROPHONE
MODEM
AUDtO
LOCAL
REMOTE
SITE
ACCESS
LONG HAUL
REMOTE
SITE
ACCESS
VOICE/DATA
MODEM
AUDIO
.AMP.
aPCAKEO
VOICE/DATA
MOO&1
AUDIO ONLY
Figure 3.2 - Video and Data Broadcast with Audio
34
the Fall 1988 with successful results.
The Control Site is the physical location where the
course is held.
It consists of work station components and
transmission facility.
In the classroom, a dedicated worJc
station is used by the instructor to display the computer
generated images on a monitor.
Simultaneously, the files
are
sites
transmitted
to
the
microwave radio link.
remote
via
satellite
and
All Remote Site work stations are
sent commands by the Control Site work station to cause each
consecutive slide to be displayed.
There are two basic types of Remote Sites:
haul
and
short
haul.
The
long
haul
site
the long
receives
its
teleconference via satellite or microwave transmission.
The
local remote site receives its teleconference via television
broadcast
and
telephone.
The Remote Sites consist of a
reception facility and work station components.
Students
sit in the remote classroom and view both a video monitor of
the
instructor
and
a
computer
monitor
which
displays
pertinent course material.
The system described in this chapter may be operated
in a lecture presentation mode or merely a file transfer
mode.
The
necessary
to
file
transfer
send
solely
mode
may
support
be
used
material
when
it
through
is
the
transmission medium.
When operated in this fashion, the
teleconference
not
does
include
a
electronic
slide
35
presentation.
The
full
motion
video
component
of
this
approach remains the same as the existing architecture with
the
addition
described
of
the
in the Video
NTSC
computer
generated
graphics
Broadcast with Audio Conferencing
Approach.
3.2.2
Detailed Description
Figure 4.2 shows the Control Site components of this
approach.
A detailed discussion is presented in Chapter 4,
Video and Data Broadcast Systems Design.
3.3
The
Data and Audio Conference
data
and
audio
conference
approach
is
a
relatively low cost choice for "improved teleconferencing."
This
approach
may
be
classified
as
an
audio
graphic
conferencing approach where the speech channel is augmented
by the ability to send a variety of material in the form of
graphics,
diagrams,
Conferencing
does
tables
not
and
include
text.
the
Data
and
Audio
communications
costs
associated with a wideband video channel nor does it derive
the benefits associated with one.
by
AT&T
software.
in
the
form
of
It is currently marketed
still-frame
teleconferencing
The name of AT&T's data and audio conferencing
system is called the Education Information Delivery System
and consists primarily of AT&T's Truevision (TM) line of
36
microcomputer graphics hardware and software [31].
It is important to note that this approach allows
for a high degree of interaction between the instructor and
the student.
drawings,
This interaction is in the form of scratch pad
picture
file
transmissions
and
the
audio
conference.
3.3.1
Operational Description
With audio graphic conferencing, grabbed images may­
be manipulated and incorporated
into the electronic slide
show, which may be distributed to other conferees in advance
through the mail on tape cartridges or telephonically using
high speed modems at night.
The
AT&T's
Telewriter3
Broadcast
images to be called up in three ways.
Software
allows
First, images can be
arranged and distributed in advance through the mail on tape
cartridges or
sent using a high speed modem.
stored at the receiving end until it is
them during the presentation.
They are
time to display
Second, slides which were
previously stored, may be retrieved, and transmitted in any
order during a teleconference.
Third, live images can be
captured and sent over the phone lines using the capture
board.
Product
information provided
by AT&T's
Electronic
Photography and Imaging Center reveals that its full color
37
files require approximately 120 seconds at 9500 baud to be
transmitted.
Reduced
color
requires
about
60
seconds.
After 15 seconds the image can be discussed because enough
black
and
white
pixel
image
has
been
sent
to
make
the
picture recognizable.
The
files
may
be
broadcast
to several
sites using the Alliance system developed by AT&T.
the
AT&T
Network,
the
Alliance Services
different
Based on
bridge lets
one
connect personal computers at up to 58 other locations on a
common telephone line.
With audio graphic conferencing, the
Alliance Services is used to connect the remote conferees to
the main site.
Voice is transmitted on this system as well
as presentation and scratch pad information.
3.3.2
Detailed Description
The hardware component of this system is shown in
Figure 3.3.
The graphics boards let one grab full-color
images from a video source in real time and display them on
a variety of monitors.
The graphics board has high color-
resolution and medium to high spatial-resolution.
A variety
of image PC-based frame grabbers may be used.
The most
popular is the Truevision Advanced Raster Graphics Adapter
(TARGA) board model 16.
RGB
video
The TARGA 16 board takes a analog
camera source and
produces
resolution with 32,768 possible colors.
a 512
x 480
pixel
The board includes
38
rh
CAMERA
/
IBM COMPATIBLE
OJMPUTER
IMAGE CAPTURE
BOARD
sm
COMPRESSION BOARD
GRAPHICS CARD
SERIAL PORT
DATA MODEM
MICROPHOfe
AUDIO
VOICE / DATA
r«DEM
19iKBS
DATA
<53-
Figure 3.3 - Data and Audio Conference
TELEPMJNE
CONFEREfCE
BRIDGE
39
a half megabyte of RAM as well as a built-in hardware zoom,
pan, and scrolling.
or NTSC output.
The TARGA 16 board can produce an RGB
The camera produces a RGB or NTSC composite
signal as a video source for the image capture board.
The Video Display Adaptor with Digital Enhancement
(VDA/D) may be used in place of the TARGA 16 board for those
remote sites that need only to display the images without
having to grab them.
The three basic Truevision software products which
are
used
in
the
generation
teleconference are described
Processing
Software,
or
and
here.
TIPS,
presentation
The
allows
of
the
Truevision Image
for
a
variety
of
functions to be performed on the images created by the TARGA
16 board.
colors
With the TIPS software, one can airbrush, change
copy
portions of
the
screen,
move
items
componements, or eliminate them altogether.
and
add
With drawing
functions, TIPS allows one to create his own graphics from
scratch.
PC
Carousel
assistant create
disk.
lets
the
presentations
instructor
or
from the images
teaching
stored on
The images form an electronic slide show which can be
pre-timed and pre-arranged to go from one image to another
in
any
of
twelve
different
fades, dissolves, and
wipes.
Finally, the Still-Frame Teleconferencing Software or STS
sends images over telephone lines to make them available
•r«=a 1 — "h 1 mo for
ions?.
40
3.4
Video, Data and Audio Conference
Using ISDN Technology
The Integrated Services Digital Network, or ISDN,
will be a world-wide digital network offering a wide range
of voice and data services based on 64 Kbits/s channels.
Although the ISDN will most likely be comprised of logically
separate
networks,
it
will
provide subscribers
with the
functionality of a single, integrated network by offering
standardized, integrated user access to services.
3.4.1
Operational Description
Since ISDN allows the user to "call-up" any type of
service
on
demand,
many
types
configurations are feasible.
and
audio
likely
be
conferencing
determined,
rather than
by a
of
applications
and
The approach to video, data
using
ISDN
technology
in the future,
standardized
media
session
format.
will
most
by session
Some class
sessions might require computer or data applications whereas
others do not.
The set of features potentially provided by an ISDN
communications
feature
that
architecture
is
sure
to
is
be
virtually limitless.
available
directional video teleconferencing.
early
is
One
multi­
Ideally, the digitally
encoded video image generated at the classroom is sent to
each remote location throughout the entire lecture.
At some
41
point in the lecture a remote site student at any location
may have a question which he would be able to transmit.
A
second video broadcast session is established which again is
circuit switched either to every other remote location or
solely to the instructor.
Potentially, any student could
have a very direct interaction with the instructor.
Instructional
computer
conferencing
is
another
feature which has potential to be an ISDN teleconference
forerunner.
Instructional computer teleconferencing could
take many forms.
of
students
In one application, each student or pairs
have
access
to
a
computer
terminal
communicate with every other student and instructor.
to
The
instructor could present a realistic scenario which would
challenge the students to work with one another in solving
the problem.
Computer access would also allow the students
to communicate freely with the instructor during the class.
Access
to
shared
computing
facilities
students
expanded
is an
power
data
bases
and
educational tool
in
solving
even
remote
which allows
problems.
ISDN
networking to other computing facilities could permit the
instructor to demonstrate the most current technologically
advanced approaches
used by industry or other university
research centers.
Also, audio conferencing in stereo might
be
an
provided
conferencing
as
options
added
feature.
provide
the
The
highest
above
degree
ISDN
of
42
interaction possible without actually being there.
3.4.2
Detailed Description
The
educational
teleconferencing
application
area
described in this section requires channels for voice, data
and video.
Figure 3.4 shows a possible configuration for
the ISDN information flow.
ISDN Access Node.
The ISDN terminal connects to an
The data channel requirements for this
application call for the basic access of 2B + D, where the B
channels are 64 Kbps and the D channel is 16 Kbps.
The two
B channels are used for the voice and computer generated
data.
Additionally, a broadband channel is necessary for
the video.
would
A modular and flexible design for broadband ISDN
allow
services
and
subscribers
to
be
expanded
in
stages without large changes in the network. The channel
rates vary for video and High Definition Television (HDTV),
but
at
this
time
we
shall
consider
an
IIH (1536
Kbps)
channel for the video signal.
The 16 Kbits/s D channel provides for intelligent
out-of-band
signaling
and
user
control.
The
user
may
control both the network connections and the delivery of
user services and applications.
This channel translates to
a Packet Switched Network and Signalling System No. 7, shown
also in Figure 3-3. The D channel may allow conferees to
specify the use of a Teleconference Bridge.
43
REMOTE
ISDN TERMINALS
ACCESS
NODES
CURCOIT SWITCHED NETWORK
DATA
/
MULTIPOIHT AU>IO AND >
AUDtO-GRAPHICS TELECONFERENCE;
BRIDCE
DATA
IICE
VOICE
VIDEO SWITCH
VIDEO
PACKET SWITCH
/ NETWORK V
SIGMALLING SYSTEM
Figure 3.4 - ISDN Information Flow for Video, Data and
Audio Conferencing
44
The multiplex and switching technology used within
the
ISDN
network
is
an
important
topic.
The
ISDN
application calls for a Multi-point Audio and Audio-Graphics
Teleconference
datachannels
terminals.
through
Bridge (MAATB).
from
the
This
Control
Site
device
to
bridges
the
the
remote
ISDN
Each ISDN terminal connected to the conference
the
bridge
broadcast data.
receives
an
identical
copy
of
the
The video teleconference bridge performs an
identical function at higher data rates.
The
UA's
new
5ESS
Switching
System,
to
be
operational in the 1990's, can be used to build and test
this approach [16].
and
software
The 5ESS switch has modular hardware
architectures
and
its
feature-customization
capabilities provide this flexibility, and form the base for
The 5ESS switch provides both the
adding ISDN capabilities.
CCITT standard, 2B + D basic-rate interface and 23B + D and
30B + D primary rate interfaces.
The AT&T Technical Journal
[16] indicates that plans are being formulated by AT&T to
build incrementally on the 5ESS switch ISDN architecture the
components
that
will
further
enhance
the
switch's
capabilities for universal information services.
Services such as the Multi-point Audio and AudioGraphic Teleconferencing Bridge devised and shown Figure 3.4
should
be
approaches
proposed
are
as
available
a
research
in
option.
combining
the
Countless
5ESS
ISDN
45
communications
architecture
teleconferencing system.
with
the
UA
Microcampus
CHAPTER 4
VIDEO AND DATA BROADCAST SYSTEM FUNCTIONAL DESIGN
The purpose of this chapter is to outline the design
specifications for the combined design approach for video
and data based delivery.
4.1
Overview
The design described
Variations on th.e basic
in this chapter is modular.
design may be made to tailor the
teleconference to the changing needs of users, and to keep
current with technological advances.
design
degree
are suggested
of
in
interaction,
Section
at
the
6.3
Modifications to this
to
cost
create
of
a
added
higher
system
complexity.
4.1.1
Design Choice
The
video
ideal
display
material.
of
educational
both
the
teleconference
includes
presenter
the
and
a
course
The Data Conference Approach provides the digital
display of class notes yet lacks the video component.
The
Video and Audio Broadcast Approach has the video component
but lacks the benefits derived from the data conference.
The ISDN approach is an ideal solution.
However, other than
ISDN primary access service, the wideband service necessary
46
47
for video teleconferencing will not be available for years
to come.
Thus, Video and Data Broadcast approach is selected
for further study.
It combines the benefits derived from
both the Video and Audio Broadcast Approach and the Data
Conference Approach.
The technology necessary for the Video
and Data Broadcast approach is presently in existence, and
is
far less expensive than a two channel video broadcast
alternative.
4.1.2
System Organization
The system components and information flow are shown
in
Figure
4.1.
The
three
major
facilities
in
the
teleconferencing system are the Control Site, Remote Sites
and Lecture Generation Support Facility (LGSF).
Site is the
held.
It
physical
consists
The Control
location where the course is being
of
transmission facility.
the
work
station
components
and
As noted, there are two basic types
of Remote Sites: long haul and short haul-
The long haul
site consists of the site which receives its teleconference
via satellite or microwave transmission.
The local remote
site receives its teleconference via television broadcast
and telephone.
Control
and
For the purpose of this discussion, the
Remote
sites
are
divided
reception/transmission facility and work station
into
the
48
REMOTE
SITE
(LONG HAUL)
LECTURE
GENERATION
SUPPORT
FACILITY
RECEPTION
COMPONENTS
WORKSTATION
COMPONENTS
REMOTE
SITE
(LONG HAUL)
CONTROL SITE
TRANSMISSION
COMPONENTS
CONFERENCE
COMPONENTS
UNIVERSITY
BROADBAND
NETWORK
REMOTE
SITE
(LOCAL)
EVAX
REMOTE
SITE
(LOCAL)
Figure 4.1 - System Components and Information Flow
49
components.
The LGSF is an independent facility used to
support the generation and distribution of course material.
The system described in this chapter may be operated
in a lecture presentation mode or merely a file transfer
mode.
The
file
transfer
mode
may
be
used
when
it
is
necessary to send solely support material.
When operated in
this
not
fashion,
the
teleconference
does
include
an
electronic slide presentation.
The
Control
Site
broadband
network
so
connected
to
network
the
that
is
a
linked
user,
may
to
the
perhaps
transfer
his
at
university
the
file
control site for later transmission to remotes.
LGSF,
to
the
Also, in
another application, the instructor at the control site may
remote
login to the
conference to
Engineering
demonstrate
an
Vax
or
"EVAX"
application
during
program.
a
This
remote login demonstration uses the NTSC encoding feature of
the
design.
allows
the
One
last
instructor
application
to
make
of
files
this
connectivity
available
from
the
electronic bulletin board on the Control Site work station.
4.2 Control Site
4.2.1
Conference Components
As shown in Figure 4.2, the conference components
of the Video and Data Broadcast design include the audio,
video and data sub-components.
50
COPJTROL
SITE
TRANSMISSION
LARGE
PROJECTION
SCREEN
FACILITY
VIDEO
DATA
( 6MH2)
VIDEO
0-4.2 MHZ
MOUSE
AUDIO
VIDEO
SWITCH
COURSE NOTE
PRESENTATION
SOFTWARE
NTSC
ENCODER
-€
cga 01aphics
serial ports
MICROPHONE
modem
AUDIO
voice/data
modem
local
remote
site
access
voice/data
modem
long haul
remote
site
access
AUDIO ONLY
Figure 4.2 - Control Site Conference Components
51
4.2.1.1
teleconference
Audio.
must
The audio portion of the
be
expanded
from
the
existing
three
line conference to that of conferencing each remote site
location.
provide
The two functions of the audio conference are to
an
audio
feedback
for
all
remote
sites
and
to
provide a low speed data transmission from the Control Site
to the Local Remote sites as outlined in Section 4.3.2.3.
Ideally,
an
audio
conferencing
bridge
should
provide smooth voice switching and distribute signals with
equal strength to all locations.
It should also protect
against noise, echo and transmission loss, and, in general,
assure good audio quality.
Noise on telecommunications channels originates from
a number of sources: amplifiers, line induction, cross-talk
and background noise at the end locations.
Echo refers to
reflections of signal energy that cause it to return to the
transmitter or receiver.
This is rarely a major problem
over short distances, but can be important over the long
haul.
Transmission
loss
or
signal strength with distance.
role
in
minimizing
and
attenuation
is
the
loss
in
The bridge has an essential
balancing
the
effects
of
these
factors to provide an acceptable sound quality.
Audio
bridging
may
be
performed
using
a
central
service or by obtaining an on-premises bridge.
The AT&T
ALLIANCE
or
Service
allows
for
multi-point
audio
audio
52
graphic
conferencing
locations.
This
by
bridging
service
is
up
to
59
separate
obtained
by
calling
the
ALLIANCE Service phone number and following the procedures
to add
a party to the conference.
The Quorum Teleclass Bridge provides almost the same
type of service as the ALLIANCE Service by accommodating up
to 20 audio conferences in as many as 3 groups.
In this
design two separate groups will be utilized, one for the
Local
Remotes
and
another
for
the
Long
Haul
Remotes.
Conferencing bridge equipment is bought off the shelf and is
easily installed by replacing the existing three line audio
bridge with the new one and
lines for each remote site.
adding the additional phone
Both Local and Long Haul Remote
work stations will access the bridge.
Local remote students
access
to
the
voice
data
modems
receive
their
DISPLAY.COMMAND messages form the Control Site work stationThe Teleclass Bridge allows modular expansion to over 100
audio locations.
Notice in Figure 4.2, one leg from the
bridge
audio
provides
input
to
the
speakers,
VCRs,
Satellite, Microwave and other production equipment.
Although either bridging approach is acceptable, the
on-premises
Quorum
Teleclass
Bridge
is
selected
as
the
preferable option, because many of the conferees are local
to the conference control site.
As a result, purchase of
the on-premises bridge results in reduced toll charges as
53
compared to the service charges associated with the ALLIANCE
Service.
4.2.1.2
Video.
The
video
components
for
the
Control Site are the same components as those described in
the
Video
Section
Broadcast
3.2.
The
with
only
Audio
change
Conference
from
the
approach
existing
in
video
Microcampus architecture is the addition of the NTSC encoded
computer generated graphics.
4.2.1.3
Data.
The data broadcast portion of the
conference is centered around the same computer work station
used to produce the computer generated graphics discussed in
Section 3.2 Video Broadcast with Audio Conference.
Two RS-
232C serial ports are used to transmit data to the Control
Site Transmission Facility.
MS-DOS is selected as the operating system
Control Site work station.
for the
Though MS-DOS does not support
multi-tasking, it does provide the programming environment
to perform the integrated tasks outlined in Section 4.2.3
Control Site Software.
users, supports
software
a
products,
MS-DOS is familiar to many computer
large number of
and
provides
different
the
presentation
necessary
operating
environment for this application.
The
MODE command
of
MS-DOS lets one define some
54
operating
characteristics
of
the
computer.
The
RS-232C
serial interface ports may be selected to run at 110, 300,
600, 1200, 2400, 4800, 9600, or 19,200 baud on the latest
version of MS-DOS.
Although, at this time, a maximum of
9600 baud will be used, it is conceivable in the future that
a 19,200 baud circuit be tested.
The COMl RS-232C serial port is used to send data to
the long haul remote sites, while the COM2 port provides
data broadcast to local sites.
port
will
be
9600
bits
per
The baud rate for the COMl
second.
This
parameter
verified in the performance evaluation in Chapter 5.
is
The
COM2 port is set to 1200 baud because only short display
messages
will
be
passed
to
local
remote
sites
telephone lines connected to the audio bridge.
over
Available
voice/data modems on the market operate with a 1200 baud
data channel rate.
An
IBM
PC/AT
compatible,
running
at
16
MHz,
is
sufficient to perform the processing tasks of the control
site work station.
memory.
The
work station must have 640 KB of
The IBM Storyboard Plus file display program. Story
Teller, described in Section 4.2.3.2 Presentation Software,
uses
approximately
software
may
use
75
up
KB
to
of
150
RAM.
KB.
Other
The
presentation
telecommunication
additions to the presentation software may include up to 50
KB more of memory, while the main program control requires
55
up to 50 KB additional memory.
presentation
package
The main program control and
including
the
telecommunication
additions along with associated data structures, all reside
in
RAM
to
eliminate
disk
access
times.
The
entire
presentation package will not constime more than 200 KB of
RAM.
An additional
15 KB of
RAM is
needed to run the
electronic mouse to advance slides.
The
average
access
time
for
PC
hard
disks
is
sufficient for this presentation application and is not a
major factor in disk selection.
5
1/4
inch
or
recommended.
3
Presentation from a floppy
1/4 inch disk is
too slow
and
is
not
A floppy drive is needed to load a new story
on to the hard disk before a lecture.
The work station should have a minimum of 30 MB hard
disk.
about
An average lecture contains up to 75 slides, taking
500
KB
of
disk space.
Additional
required to store support material.
disk
space
is
The work station should
have a minimum of 30 MB hard disk to provide support for the
current
lecture and
instructors.
maintain recent
lectures
for several
The lecture room is equipped with large screen
projection equipment to display the course material.
4.2.2
Transmission Components
4.2.2.1
the
NTU
Satellite. The
satellite
based
existing
teleconferencing
conficfuration
of
architecture
is
56
discussed in Chapter 1.
NTU leases one transponder on the
satellite which has an available bandwidth of 54 MHz with a
carrier
frequency
of
11,974
GHz.
NTU
broadcasts
channels simultaneously over one transponder.
This approach
results in NTU receivers requiring a 22 MHz band width.
NTSC
color
subcarrier
signal
requires
frequencies
exist
about
at
5
two
MHz.
The
6.2 and 6.8 MHz.
The
audio
See
Figure 4.3 for the signal channel spectrum of the satellite
system.
Only one of the two audio channels is used in NTU's
present configuration.
The opportunity exists to modulate
data on the unused audio channel.
audio
subcarriers
in
The minimum band width of
satellite
modulation
is
although three times that band width is common.
the
second
audio
channel
requires
current
15
KHz,
The use of
satellite
receivers to have two audio subcarrier demodulators.
Figure
Transmission
4.4
shows
Components.
the
The
Control
modulated
Site
signal
Satellite
from
the
digital output of the COMl RS-232C port will be converted
from digital to analog.
The carrier frequency of the analog
signal must be within the audio range.
the modulated signal is then split.
second
of
two
satellite
The analog signal of
One leg is input to the
audio channels, while the other
feeds the microwave audio channel.
4.2.2.2
Microwave Radio.
As discussed in Chapter
Q - 6.0
6.2
6.3 RIHC
VIDEO
AUDIO 2
DATA
AUDIO I
SATELLITE
AUDIO
HZ
DATA
'15
KHZ
./IDEO
T
100
6 MH2
KHZ
5U8CARR1ER
MICROWAVE
Figure 4.3 - Signal Channel Spectriam
POWER
AMPLIFIER
14 GHZ
UP
CONVERTER
VIDEO
MODULATOR
AUDIO CH 2
AUDIO CH 1
T
UJ
O
>
o
•V
CONTROL SITE CONFERENCE COMPONENTS
Figure 4.4 - Control Site Satellite Transmission Components
59
1, the Fort Huachuca video linkage currently exists as a one
way transmitter originating at the University of Arizona
Microcampus. As a simplex circuit, there are modulators and
transmitters on the University of Arizona Control Site side
and demodulators and receivers on the Fort Huachuca side.
The
current
analog
microwave
radio shot
transmitter and receive sides.
in
degraded
two
The video signal is split
and transmitted on both wideband channels.
received
consists of
quality,
the
When one side is
receive
at
Huachuca end is patched over to the backup side.
the
Fort
Some time
latter troubleshooting takes place and the degraded side is
restored.
The Microwave Video Radio (MVR) system used on this
link
has
the
capability
of
transmitting
at
a
carrier
frequency band of 1700 to 2300 MHz. This link has A side and
B side transmitters and receivers.
There are three separate
microwave hops from University of Arizona to Fort Huachuca.
The
A
and
B
side
transmitters
have
different
transmit
frequencies within the above frequency band for each hop.
The transmission capability of this radio allows for
one
NTSC 525 or 625 line video channel and up to four optional
subcarrier channels.
There is no available band width for
an additional video channel, though, the subcarrier channels
offer us some great potential.
The subcarrier channels for the MVR
are designed
60
with the following two options: a 40 Hz to 15 Khz frequency
input or a 40 Hz to 100 KHz frequency input.
sub-carriers may
be purchased
for this
Four of these
particular radio.
Only one subcarrier exists currently on the radio shot.
The
coupling
FM
subcarrier
subsystem
modulation
to
a
to
modulator
apply
subcarrier
broadcast
spectrum
on
the
quality
microwave
used
in
a
video
an incoming audio signal as
that
particular module in our radio.
provides
is
FM
is
developed
by
this
The subcarrier modulator
channels
above
radio baseband.
the
video
The existing
configuration consists of one subcarrier channel strapped
with a 40 Hz to 15 KHz band width.
This subcarrier carries
the audio signal from the lectureA change of strapping option to a 100 KHz bandwidth
subcarrier channel creates the
potential to transmit the
required 40 Hz to 15 KHz audio signal plus a modulated data
signal within the 50 to 100 KHz range.
Control
above.
Site
microwave
transmission
Figure 4.5 shows the
components
discussed
To avoid confusion, both Figures 4.4 and 4.5 for the
satellite
and
microwave
facilities
modulator for the digital signal.
each
show
a
separate
In actual implementations
only one digital to analog modulator is used to feed both
transmission facilities.
4.2.2.3
Television Broadcast (ITFS).
Local remote
sites within the surrounding ITFS television broadcast range
61
1730 MHZ
VIDEO
40H2-tOOKH2
band pass
digital to
analog
modulator
H
subcarrer
modulator
transmitter
—(filter
50-100 KHZ
DATA
AUDIO
VIDEO
CONTROL SITE
CONFERENCE COMPONENTS
Figure 4.5 - Control Site Microwave Transmission Components
62
will receive a video image as they do now in the existing
system.
or the
This video image will be either of the instructor
computer
graphics
converted
via the
NTSC encoder
described in Section 3.2.
The transmission media for course notes and support
files
will
be
telephone
based
to
take
advantage
of
inexpensive telecommunication charges.
The
satellite
and
microwave
transmission
systems
have the band width capacity to send files in the future at
substantially higher data rates, while the telephone system
presently
used
has
comparatively
limited
data
rates.
Section 4.4 discusses the possible near term requirement for
higher transmission speeds essential for real-time display
of high resolution graphics.
As an example, the AT&T Data
and Audio Conferencing approach
described
in
Section 3.3
requires approximately 120 seconds at 9500 baud for a 512 x
480 pixel color resolution image to be transmitted fully
over telephone lines [31].
telephone
system
Since limited band width of the
prohibits
satisfactory
real-time
transmission of high resolution graphics, data transfers to
Local Remote Sites using telephones, will occur both before
and during the lecture.
Data files and support material will be sent to the
remote site via the electronic bulletin board system prior
to the lecture whereas presentation commands to change the
63
slides will be sent real-time during the lecture.
design upgrade to the Telecommunications Package
A future
for the
Control Site work station might allow file transfer to Local
Remote Sites through the voice/data telephone channel.
A
discussion of the Telecommunications Package may be found in
Section 4.2.3.2.
The Conference Control Work station has two serial
RS-232C communication ports.
The COMl port will be used for
transmission via satellite and microwave, while COM2
be connected to a teleconferencing bridge.
commands
will
associated
board
data
system
be
sent
files
to
will
the
local
Only display
users
because
be sent through the
described
in
Section
will
the
bulletin
4.4.
The
teleconferencing bridge is discussed in Section 4.2.1.3.
Files sent in advance using the
bulletin board system falls
within the scope of the Lecture Generation Support Facility
(LGSF) described in Section 4.4.
An announcement may be
made by the instructor if additional files are available on
the electronic bulletin board system and last minute changes
may be made available shortly after the lecture.
4.2.3
Control Site Software
An
overview
of
presented in Figure 4.6.
the
control
site
software
is
The three main components of the
Control Site Software are the Main Process, Presentation
64
Software (PS) and Teleconununications Package (TP).
The Main
Process includes the initialization routines and statistical
display routine, and calls the PS and TP when appropriate.
Control site software is purposely designed in a modular
format
to allow for flexibility.
Different presentation
packages may be integrated into the design easily.
4.2.3.1
Main Process.
The main process controls
the overall running of the Conference Control Software.
activates
the Presentation Software and
Package
when necessary.
process
operates
is
detail
of
the
how
A
description
contained
Main
Telecommunication
of
how the
in this section.
Process
It
interfaces
main
Further
with
the
Telecommunication Package and Presentation Software is given
in the Simulation Listing in Appendix A.
Initially, the Main Process queries the instructor
to begin a lecture.
files
to
be
The lecture must specify the display
presented
and
the
support
files
to
be
broadcast.
Next,
the
Telecommunication
main
Package
process
(TP).
must
The
Package is described in Section 4.2.3.2.
call
up
the
Telecorimunications
The TP must run
before files may be displayed because simulation results
showed that some of the first few slides of a lecture were
not being received correctly before the first
BEGIN
SPECIFY
LECTURE AND TRANSMIT
FILES
TRANSMIT
HEADER INFORMATION
N TIMES
TELECOMMUHICATIOMS
PRESENTATION
PACKAGE
SOFTWARE
DISPLAY
TRANSMIT
STATISTICS
r END >
SESSION?
NO
YES
END
Figure 4.6 - Overview of Control Site Software
56
DISPLAY.COMMAND was received from the Control Site.
The
number of different files sent in advance is an adjustable
parameter in the simulation.
The main
Software (PS).
process then starts up the Presentation
The PS displays the first slide and then
reverts back to the main process.
If no keyboard entries
are received by the Main Process, control is passed to the
Telecommunication
Package.
The Telecommunication
package
determines which file should be sent next. After a file is
sent
by the Telecommunications Package, control is passed
back to the Main Process.
Three types of keyboard entries may be received and
interpreted by the Main Process and Presentation Software.
The possible entries
carriage
return,
indicating
slide, a "+" or
go
back
one,
are a numeric
the
string followed
display
of
a
by a
particular
indicating to display the next slide or
an
<esc>
key
indicating
presentation or a invalid key sequence.
the
end
of
a
A display command,
such as advance to the next slide or go back one, results in
calling up the TP to send a command packet, after which
control is passed to the Presentation Software where the
slide is displayed locally.
When the last slide is displayed the PS sets the
End.Of.Presentation flag which results in the main process
invoking
the
Telecommunications
package,
with
an
67
END- OF.PRESENTATION command.
Control is passed back to the
Main process which subsequently concludes by executing the
Display.Transmit.Statistics Routine.
The statistics routine
accesses the transmit file tables and alerts the instructor
if any files were never sent.
The main process queries the
presenter to see if the presenter cares to end the session.
4.2.3.2
has
been
design.
Presentation Software.
selected
as
the
IBM Storyboard Plus
presentation softv/are
for this
IBM Storyboard Plus consists of the following
five
major parts that are used for story creation and display:
Picture Maker, Picture Taker, Story Editor, Story Teller and
Text Maker [18].
The Picture Maker allows the instructor to create
pictures
Maker.
and
modify
previous
pictures
saved
by
Picture
A "mouse" is used to draw free-form figures, boxes,
lines and ellipses.
may be created.
Various fonts and forms of graphic text
The Picture Taker allows the contents of
screens created by IBM Personal Computer DOS programs to be
"captured" and saved on disk for later inclusion in a story.
The Story Editor allows you to display pictures previously
made
by
Picture
Maker,
Picture
Taker or
Test
Maker
and
sequence those pictures into stories using special dissolve
techniques both between pictures and within pictures.
Story Teller allows you to display stories previously
The
68
created by Story Editor.
Text Maker allows you to create or
modify text screens created with Text Maker.
Although this design centers around the Storyboard
presentation software, other presentation software products
may be selected to be integrated into the teleconferencing
design package.
software
The key criteria is that the presentation
responds
to
interrupts
communication handling routines.
and
branches
to
IBM Storyboard Plus allows
easy jumps to predesignated memory locations.
The routines
are the implementations of the protocols described in the
next section.
4.2.3.3
Telecommunication Package.
The broadcast
protocol for transmission of files and control commands was
developed
specifically
application.
for
this
teleconferencing
The Microcampus application calls for the use
of existing satellite and microwave wideband channels for
the
distribution
of
the
data.
Both
types
of
wideband
channels are uni-directional or simplex.
The objective in protocol design is to develop a
working
protocol
application.
that
is
simple
yet
adequate
for
the
Figure 4.7 shows the flow chart structure of
the algorithm.
The DETERMINE.NEXT.FILE routine determines which
file should be sent next.
It maintains a SEND.FILE.INDEX
69
START
INSTRUCTOR
INPUT ->
SPECIFY STORY/FfLES
TO SEND
SEND HEAOERXnO
INCR(HEAOER.CNT)
-^HEAOERXHf^
^ .REPEAT.HEA0ER3
Y£S
iNCR<FILE.CNT}
.^-^ILEXirns^
.N.FILESJkHEAD *
^REPEAT.FILES 2-
BEGIN LECTURE
YES
EMO
^
PRESENTATION?
I
YES
s?SD
ERniNAL.SUFFER
^ - EMPTY? ^
YES
END.PRESENTATiON
MESSAGE
NOTIFY INSTRUCTOR
OF UNSENT FILES
YES ^^TERM.BUFFER"^
= <£SC> OR
\|1I0.DISPUAY^-^
END
END.PRESENTATION
= TRUE
Figure 4.7 - Control Site Telecomunications Package
70
which represents the file nxmber to be sent next.
is
sent
.REPEAT.FILES
times
to
help
insure
Each file
a
file
received without errors by the time it is displayed.
is
When
the routine has cycled through the files that need to be
sent,
the
N.CYCLED
DETERMINE.NEXT.FILE
variable
routine
is
is
incremented.
called,
it
When
the
compares
the
CURRENT.DISPLAY variable to the SEND.FILE.INDEX.
If the
SEND.FILE.INDEX has already been displayed and the routine
has
not
cycled,
following
the SEND.FILE.INDEX
the
CURRENT. DISPLAY
is
file,
set
to
the
file
otherwise
the
SEND.FILE.INDEX file is sent and variable is incremented.
DETERMINE.NEXT.FILE routine is implemented in detail in the
simulation
listing.
Appendix
A.
A
simple
scheme is used to detect transmission errors.
block
parity
The parity
bits are computed for every n or fewer bits transmitted.
The
parity
bits
added
to
the
end
of
the
message
are
rechecked at the remote site to determine if there was an
error.
As
modeled
station
only
if
files
they
are
saved
contain
by the
fewer
remote
errors
work
than
corresponding file previously received.
4.3
Remote Site
As noted previously, there are two basic types of
Remote Sites, long haul and short haul.
The long haul site consists of the site which
a
71
receives
its
teleconference
transmission.
teleconference
Thebasic
though,
The
via
components
the
different.
via
local
remote
television
of
the
operations
of
satellite
site
broadcast
Remote
or
Sites
microwave
receives
its
and
telephone.
are
the
the work stations is
same,
somewhat
The Long Haul Remote Site is depicted in Figure
4.8 and the Local Remote Site is shown in Figure 4.9.
4.3.1
Work station Components
The work station hardware components is the same for
all remote stationsSince little processing
occurs at the Remote Site,
the required processing speed for the remote work station is
less than that required of the Control Site work station.
The majority of the processing power at the remote site is
used to display the picture files and check for errors in
the
received
maintains a
files..
The
remote
work
data structure on received
station
software
file status.
In
addition to the "on-line" processing performed during the
conference, the same work station may be used during nonconference periods as the Bulletin Board System or BBS.
The
Presentation
Software,
combined
with
the
Telecommunications Package, runs during the conference in
the remote work station.
This software as described in
Section 4.3.2, Remote Work Station Processes, requires
72
CONFERENCE
CONTROL
FACILITY
LONG HAUL
REMOTE
SITE
[IR'
VIDEO, AUDIO
DATA
CONTROL SITE
TRANSMISSION
FACILITY
& a a
COMPUTER
MONITOR
VIDEO
remote
site
reception
facility
CONFERENCE
CONTROL
CENTER
N.
\
o o o
' TELEVISION
MONITOR
a
t COMPUTER
±
A
AUDIO
(.OPTIONAL)
university
computing
facilites
^ MOM-CONFERENCC^
^
DATA
•
DATA
—(coMPurreJ
modem ,
PAGE
SCANNER
Figure 4.8 - Long Haul Remote Site Components
_L
ixaot pwtwcR
73
LOCAL
VIDEO / AUDIO
CONTROL
FACILITY
REMOTE
FACILITY
^
Vf
BROADCAST
few
.MFL
CONTROL SITE
TRANSMISSION
FACILITY
1
a A <5
o o o
COMPUTER
MONITOR
VIDEO
S-
TELEVISION
MONITOR
CONFERENCE
CONTROL
CENTER
ir=
R COMPUTER.
fkHCEytiATA
r-
UNIVERSITY
COMPUTUIG/
LGSF
LOV SPEED DATA
•
AUDIO
NOW-COHFERENCE
DATA
^
i modem
PATA
^ oiMPurtR^
"m modem ,
PAGE
SCANNER
Figure 4.9 - Local Remote Site Components
^
LASmWWCR
74
approximately 200 KB of RAM.
This niimber depends primarily
upon the size of the particular presentation software.
IBM
Storyboard
Plus
presentation
Teller" requires 75 KB of RAM.
software
called
The
"Story
The additional memory is
used by the Reception Telecommunication Package.
Only 512
KB of memory is necessary for the remote work stations.
The workstation's hard disk should be at least 20
MB.
If, in addition, the
should
allow
a
minimum
of
BBS resides on the disk, one
30
MB
for
its
use.
Taking
everything into account the size of a remote work station
hard disk should be as a minimum 30 to 40 MB.
Disk access
time must be reasonably short to allow a picture file to be
retrieved and displayed within 1/2 a second of the command
message being received.
The standard access time for PC
hard disks is sufficient for this application and is not a
significant factor in hardware selection.
A laser printer is necessary to recreate hard copy
class notes received through the transmission system.
Also
a page scanner is recommended for transmission of material
to
the
instructor
overnight
through
the
Bulletin
Board
System described in Section 4.4 [4].
4.3.2
Work Station Processes
The software for the satellite and microwave work
stations or Long Haul Remote Sites differs slightly from
75
that
of
systems
the
local
receive
television work
only
command
stations.
type
messages
The
local
because
file
transfers are performed through the BBS.
The Remote Site processes are similar to the Control
Site
process.
Figure
reception processes.
4.10
shows
an
overview
of
the
Prior to the start of a lecture the
BBS is taken down if it resides on the same work station as
the Remote Presentation Package.
Package is executed.
Control Site.
The Remote Presentation
It waits for a header message from the
The header message specifies the STORYNAME,
and N.DISPLAY which is the number of picture files to be
shown in the story.
File and Command Packets are received at the Long
Haul
Remote
Sites,
whereas
only
Command
received at the Local Remote Sites.
Packets
are
Files are displayed
upon receipt of a DISPLAY.COMMAND from the Control Site.
At
the
end
of
the
presentation,
END.OF.PRESENTATION Command is received.
an
At this time the
Long Haul Remote Sites check the file status of all files.
If files are received in error or not received at all, the
remote user is notified by the program.
Upon notification,
the remote user makes a verbal request through the audio
feedback to the Control Site.
rebroadcast
of
specific
files.
The remote user requests
Ideally,
rebroadcast should occur infrequently.
a
request
This will be a
for
RECEIVE
HEADER MESSAGE
RECEIVE
PRESENTATION
FILES
DISPLAV
FILES
RECEIVE
END OF SESSION "
MESSAGE
CHECK
RETRANSMIT
ERROR
IN ANY
FILE?
DISPLAY
STATUS
END
Figure 4.10 - Overview of Reception Processes
77
critical
performance
parameter
in
the
simulation-
The
Local Remote Site has no need to request retransmissions
because files are sent without error through the BBS.
4.3.3
Reception Components
Reception
components
are
very
similar
to
their
transmission counterparts.
4.3.3.1
site
for
Satellite.
receiving
antenna,
low
noise
NTU
The equipment
transmissions
amplifier
or
needed at any
includes
block
down
a
Ku-band
converter,
video/audio demodulator with two audio channels (receiver)
and a splitter if two simultaneous channels are desired.
This
design
takes
advantage
of
the
two
audio
transmit
channels to pass its data.
One channel is used for audio
reception
is
while
the
other
used
to
pass
data.
The
required satellite receiver must feature two audio channel
reception.
This type of receiver is often used when two
channel stereo sound is wanted or when an "orderwire" is
needed.
Most Ku-band receivers have a two audio channel
receive capability.
The audio channel 2 output is connected
to the analog to digital demodulation equipment.
From the
demodulator, data is passed directly to the RS-232C COMl
port of the remote work station.
The telecommunications
package receives the data from the serial port buffers.
78
4.3.3.2
Microwave Radio.
The video microwave radio
is described in Section 4.2.2.2.
the
radio
microwave
signal.
receiver
baseband,
separates
The demodulator within
an
amplifies
FM
and
subcarrier
amplitude
from
the
limits
the
As discussed in Section 4.2, internal strapping
options provides an audio band from 40 Hz to
15 Khz or from
40 Hz to 100 KHz.
The wideband strapping option has been chosen.
An
analog to digital converter is connected to the output pins
of the MVR wideband channel.
The carrier frequency of the
modulated signal is well above 15 KHz to reduce bleed over
onto the adjacent audio channel.
The demodulated signal is
fed into the COMl RS-232C serial port of the computer.
The
data rate of the analog to digital converter is 9600 baud
and it evaluated in Chapter 5 Performance Evaluation.
Remote conference speakers are also connected to the
audio output pins of the radio.
An audio band pass filter
is inserted between the output pins and speakers.
4.3.3.3
Television
Reception (ITFS).
The
data
portion of the conference has two components: the real-time
remote control presentation and the Bulletin Board System
(BBS).
Both
components
utilize
transmission media (see Figure 4.9).
the
telephone
as
a
79
The
real-time
commands
are
the
display
generated by the Control Site Work station.
commands
The commands
are received through a telephone connection with the audio
teleconferencing bridge located at the central site.
connection
is
established,
the
frequency
When a
band
of
telephone line is split to utilize a portion in the
the
audio
conference, while the remainder of the bandwidth is used to
create the data conference.
The data line from the voice
data modem connects to the serial port of the remote site
work station.
The BBS system is responsible for transferring all
picture files and any support files between the instructor
and student.
4.4.2.
Details of the BBS are presented in Section
The equipment for the video reception portion of
this system does not change from that of the existing system
outlined in Chapter 1.
4.4
Lecture Generation Support Facility (LGSF)
The LGSF is a independent facility used to support
the generation and distribution of course material.
Figure
4.11 shows the components of this facility.
4.4.1
Lecture and Class Note Generation
Class note generation is performed on the LGSF work
station.
Class
notes
are
generated
using
a
picture
80
generation package.
Once all the notes are created another
application
is
program
presentation order.
used
to
arrange
the
slides
in
Section 4.2.3.1 Presentation Software
describes the Storyboard Plus software which allows for the
generation and arrangement of slides.
An
advanced
method
of
class
note
generation
through the use of an RGB camera, and digitizer.
of class
note generation
has
is
This form
been described in the Data
Conference approach outlined in Chapter 3.
A completed lecture may be hand carried on diskette
to the Conference Control Center or it may be transmitted on
the communications LAN.
University
of
Arizona
Picture files may be sent to the
Computer
Aided
Engineering
Center
where 35mm slides can be created from IBM Storyboard Plus
picture files.
4.4.2
Class Note Distribution
The LGSF has a telephone line and modem to support
the electronic Bulletin Board System (BBS).
The BBS is used
to send course material to sites that receive their course
from local ITFS television broadcast.
It may also be used
by remote long haul sites that are unable to receive any
material from their primary method of satellite or microwave
transmission, i.e., if they have equipment problems or
81
CAMERA
LASER PRINTER
IBM COMPATIBLE
COMPUTER
IMAGE CAPTURE
^RD
COMPRESSION BOARD
GRAPHICS CARD
SERIAL PORT
DATA MODEM
DATA
BULLETIN BOARD ACCESS
UNIVERSITY
BROADBAND
NETWORK
Figure 4.11 - Lecture Generation Support Facility
82
choose
to
advance
the
data
portion
of
the
conference
independently.
The
student
and
Bulletin
Board
instructor to
located computer system.
System
or
BBS
exchange files
allows
every
in a centrally
The BBS consists of a dedicated
AT-compatible computer with a large hard disk and one or
more modems.
Most BBS offer the capability of sending mail
from user to user; up-load and down-load files; and support
multiple
phone
specialized
lines,
either
inherently
or
software package like Quarterdesk's
with
a
Deskview.
The BBS also may restrict unauthorized callers to limited or
no data access [17].
4.4.2.1
Bulletin
Board
System
Operation.
The
electronic bulletin board is composed of the control site
and remote site components.
Each BBS is needed to perform
specific functions.
The control site bulletin board system performs the
following functions:
1. Overnight delivery of picture files to remote sites.
Distribution of picture files will primarily be to a list
of local phone numbers.
2. Reception of files from remote sites when the
Central BBS calls the remote site.
3. Toll saving. When long distance calls are
necessary, the BBS should have the capability of
waiting until after peak hours to make a call.
83
4. Multiple phone capability. The control site BBS must be
able to handle multiple phone lines. Multiple phone
lines are necessary when files must be distributed to
several remote stations at
the last minute. This may
occur when an instructor has made last minute changes or
never released a copy of his file.
4.4.2.2
Board
System
BBS Choice.
for
PCs
is
RBBS-PC or Remote Bulletin
the
recommended
system for this design application.
by
Capital
[17 J.
tested
PC
It
in
Users'
Group
is the most
a
recent
and
bulletin
board
RBBS-PC is distributed
is
considered
highly recommended of
product comparison
and
shareware
many
BBS's
provides
attractive features described in the preceding section.
many
The
package internally supports many protocols and may support
external
Every
protocols, such as
file
may
be
combination of locks.
given
Kermit, Sealink,
its
own
and Zmodem.
security
level
or
CHAPTER 5
PERFORMANCE EVALUATION
A performance evaluation of the system
conducted in this chapter.
using
models
developed
in
design is
A simulation approach is used
the SIMSCRIPT
II-5
simulation
language.
SIMSCRIPT II.5 provides the necessary flexibility in
program control based on logical conditions.
allows
for
direct
correlation
and
This feature
simulation
of
the
transmission protocol developed and described in Chapter 4.
Built in distribution functions make SIMSCRIPT easy to model
the random input parameters of file sizes and display times.
The
TALLY statement
functions
also
combined
permit
with the
convenient
Mean and
creation
intervals for the extimated variables.
of
Variance
confidence
These are described
in Section 5.5.
5-1 Simulation Goals
Simulation of the system design allows for a more
accurate determination of the speeds required to transmit
the
data
over
Necessary
the
design
microwave
parameters
and
satellite
must
be
facilities.
determined
by
simulation.
It
is
important
to
84
optimize
the
transmission
85
protocol to insure files are received in good quality by the
designated display time.
Alternative protocol policies may
be compared to determine the best transmission protocol for
the system.
The bit error rate (BER) can be changed to
determine the effects of a noisy channel on the lecture.
Internal design parameters within the transmission protocol
peormit adjustment such as the:
a.
Number of files which are sent prior to the start of the
presentation.
b.
Niimber of times a file is repeatedly sent to reasonably
assure it is received correctly prior to display.
The
study
permits
us
better
control
over
the
conditions of the system which may not otherwise be readily
obtainable
in
simulation
parameters
a
real-time
effort
and
system.
permits
transmission
an
In
accurate
protocols
summary,
this
estimation
necessary
of
for
an
must
be
effective design.
5.2
In
a
Performance Variables
working
system,
all
graphic
files
available for display when demanded and pictures should be
displayed correctly (without errors).
Few, if any, files
should need retransmissions at the end of a lecture.
be
represented
by
several
These
conditions
can
performance
variables.
In particular, the following probabilities are
86
estimated:
a.
P[ # Incorrectly Displayed Slides > 0].
b.
P[ # Slides not Available for Display > 0].
c.
P[ # Files that Need Retransmissions > 0].
The files that need retransmissions. Part c., are
the files which may fall in Parts a. or b. above, yet were
never received correctly by the end of the session.
In
other words, files that need retransmission are those which
were never received without error by the end of the class
session.
5.3 Model Development
The three major components of the teleconferencing
system are the control site, consisting of instructor and
workstation, communication equipment and paths, and remote
site workstation.
Figure 5.1 shows a diagram of the system
components.
The details of the control site conference and
transmission
components
along
with
the
remote site work
station and reception components were given in the video and
data broadcast systems design in Chapter 4.
Design elements which may have some impact on the
overall system performance are included in the simulation
model.
Some
assumptions
simulation model.
can
be
made
in
describing
First, the system clock rate of the
the
CONTROL SITE
WOBK STATION
INSTRUCTOR
COMMANDS-^
com
RAM
con2
COMttUNICATJON PATHS
AND
TRANSMISSION
COMPONENTS
• SATELLITE
REMOTE SITE
• MICROWAVE
• TELEPHONE LINE
WORK STATIOM
COMt
COM2
Lf!!vj te'
Figure 5.1 - System Diagram
88
personal computers (PC) described in both the control and
remote site computers runs at 15 MHz.
exceeds
the
transfers,
rate
necessary
operating
to
This processing speed
handle
system,
the
and
serial
port
teleconferencing
application program.
Therefore, computer processing speed
is
relevant
not
considered
evaluation.
second
access.
It
a
is
factor
acceptable to
delay in displaying a
The remote disk
in
the
allow a
performance
fraction of
a
file resulting from a disk
access occurs on two occasions: to
store a file which is of better quality than that previously
received and to display a file residing on disk.
case
a
access.
display
command
may
wait
until
after
In each
the
disk
A reasonably fast disk prevents the need for adding
disk access delays to the simulation model.
A block diagram of the SIMSCRIPT II.5 model is shown
in
Figure
independent
5.2.
The
model
processes:
contains
GENERATOR,
the
following
four
TRANSMIT.AND.DISPLAY,
RSCJEIVE.AND.DISPLAY, and REPEAT. RUNS.
The
REPEAT.RUNS
process
is
responsible
for
initialization and set up of the simulation variable for
each new run or class period-
It calls the INITIALIZATION
routine which creates entities called
has
a
VIEW.TIME,
SIZE,
number
of
FILEs.
times
transmitted
N.TRANSMIT, and receive quality or R.Quality.
and
file SIZE are
determined
Each FILE
or
The VIEW.TIME
by probability distribution
89
function
discussed
functions
of
the
in
Section
5.4.
REPEAT.RUNS
confidence intervals.
The other important
process
is
to
determine
The simulation will continue until a
predesignated relative precision is obtained as discussed in
Section
5.5.
REPEAT.RUNS
process
activates
the
TRANSMIT.AND.DISPLAY and RECEIVE.AND.DISPLAY processes.
The
TRANSMIT.AND.DISPLAY
process
sends
several
header commands to the RECEIVE.AND-DISPLAY PROCESS.
The
header message alerts the remote work station of session
initialization
and
provides
the
expected to be transmitted.
number
of
unique
files
Next a message containing an
integer, .N.FILES.AHEAD, number of files are sent to the
remote
work
activated.
station
before
GENERATOR
is
A display command is issued after a wait
VIEW.TIME period has elapsed.
sent
display
The GENERATOR models the display commands issued
by the instructor.
be
the
to
the
remote
If no Display commands are to
sites
at
any
given
time,
the
TRANSMIT.AND.DISPLAY process calls the DETERMINE.NEXT.FILE
routine and sends the next file.
The DETERMINE.NEXT.FILE
routine implements the intelligent file selection protocol
discussed in Chapter 4 with implementation in Appendix A.
When
all
files
have
been
displayed
a
END.PRESENTATION
command is sent to the remote work station.
The RECEIVE.AND.DISPLAY process waits for commands
and files.
The routine CHECK.FOR.ERRORS is called when a
90
ACTIVATE REPEAT.RUN3
PROCESS
t INITIALIZATION BOUTI NC
t ACTIVATE PROCESSES
t COMPUTE CONFIDENCE
INTESVALS
END.OF.CLASS
START NEW CLASS
SESSION
INSTRUCTOR
CONTROL SITE W.S.
REMOTE SITE W.S.
GENERATOR
TR ANSnIT.AND.DISPL A V
RECEIVE.AND.OISPLAY
• DISPLAY
• OETEBniNE.NEXT.FlLE
a SEND.C0nt1AND
• SEND.FILE
DISPLAY SUDE
DISPLAY LAST SLIDE
SENO.COMMANO
SEND.FILE
Figure 5.2 - SIMSCRIPT Processes
• CHECK.FOR.ERROeS
• STORE FILE
• CHECK.RETRANS
91
file is received.
It models the communication channel by-
introducing errors in the message-
The expected Bit Error
Rate
microwave and
or
BER
from
an operational
satellite
system is estimated to be less than 1 bit error in 1.0 x
lOE-07
bits
simulation
transmitted.
1.0
x
lOE-06
is
For
the
used
to
purpose
take
into
of
account
potentially poor performance on the transmission media.
BER
parameter is varied
this
The
to determine the effect of poor
transmission channels in Section 5.5.
The equation to model the BER in the simulation is
derived from the following:
P[error in 1 bit] = BER
P[no error in 1 bit] = 1 - BER
Therefore, if independent bit errors;
P[no error in N bits] = (1 - BER)^
If
P[no error in FILE.SIZE bits] < random number
between 0 and 1, then at least one bit error occurred in
that message.
A file is stored if it is a better copy than
any previously rcccivcd.
routine
process.
CHECK.RETRANS
At the end of a CIQGG lecture, the
is
called
by
RECEIVE.AND.DISPLAY
It checks the R.QUALITY for each file to determine
if any file needs retransmissions.
Finally, the lecture
concludes and REPEAT.RUNS is awaken.
5.4 Input Parameters
92
Probability distributions are needed to model the
file sizes and display times.
File sizes vary with the
graphic contents, while display times vairy randomly with the
instructors presentation.
to
create
these
The
probability
program UNIFIT [23] is used
distribution
functions
which
most closely represent the input data.
UNIFIT
is a
state-of-the-art interactive computer
package for fitting probability distributions
data.
with observed
By combining the latest statistical techniques with
graphical
displays,
the
package
allows one to
perform
a
comprehensive analysis of a data set in significantly less
time
than
would
following
otherwise
three
activity
be
possible.
approach
for
It
employs
determining
the
an
appropriate distribution:
1.
Hypothesize one or more families of distributions which
might be appropriate,.
2.
Estimate the paraimeters for each hypothesized family,
thereby specifying a number of particular distributions.
3.
Determine which of the fitted probability models is the
best representation of the data using formal goodness
of fit tests (e.g., chi-square and Kolmogorov-Smirnov
tests)[23].
5.4.1
Observed Data
5.4.1.1
File
Sizes.
Existing
IBM
Storyboard
stories were examined to obtain raw file size data which
most closely approximates the file size data used by the
instructors.
The
IBM
Storyboard
Plus
stories
contain
93
picture files which are created with a resolution of 320 by
200 pixels where each pixel is one of four colors.
Analysis of Storyboard picture files results in the
following general observations on file size:
1.
Graphic Picture files do not differ significantly from
files containing mainly graphic text.
2.
Complicated background patterns such as checkers add
substantially to the file size, although few files
maintain this feature. (Probably because the foreground
tends to get lost in the background.)
3.
very busy graphic files were comparatively tne same size
as large graphic text files.
A
from
two
histogram
showing
existing
observed
stories
file
size collected
for
instructional
used
presentations is shown in Figure 5.3.
Table 5.1 shows that
the mean file size is 5,325 bits while the median is 5,406
bits.
The minimum file size is 2,831 bits.
The IBM Story
Board Plus Picture Maker appends a 2,000 bit header to each
file, therefore, file sizes will never be under 2,000 bits.
5.4.1.2
Display
viewing
video
Times.
of
Display
tapes
times
Microcampus
were
collected
by
class
lectures.
While an instructor flipped from one slide to the
next, a stop watch was used to time the period each slide
was displayed.
A histogram and statistical calculations of
observed display times is shown in Figure 5.4 and Table 5.2
respectively.
The mean display time for the sample is 74
94
11109F
8-
R
E
7-
Q
6-
U
E
5'
N
4-
C
3-
Y
2'
10
2.5
5.0
7.5
10.0
FILE SIZE (KB)
Figure 5.3 - Histogram of Observed File Sizes.
SAMPLE
CHARACTERISTIC
NUMBER OF OBSERVATIONS
MINIMUM OBSERVATION
MAXIMUM OBSERVATION
MEAN
MEDIAN
VARIANCE
LEXIS RATIO (VAR./MEAN)
COEFFICIENT OF SKEWNESS
COEFFICIENT OF KURTOSIS
VALUE
90
2831
1.00920E+
5325.41
5406.00
2.16581E+
406.694
.50138
3.00938
Table 5.1 - Observed Sample Statistics.
95
8
F
7
R
E
6
Q
u
5
E
4
N
C
3
Y
2
1 -t
0
60
120
T
180
240
DELAY TIME (SEC)
Figure 5.4 - Histogram of Observed Display Times.
SAMPLE
CHARACTERISTIC
NUMBER OF OBSERVATIONS
MINIMUM OBSERVATION
-MAXIMUM OBSERVATION
MEAN
MEDIAN
VARIANCE
COEFFICIENT OF VARIATION
COEFFICIENT OF SKEWNESS
COEFFICIENT OF KURTOSIS
VAI.tJE
76
10.0000
243.000
74.3158
66.0000
2358.57
.65349
1.39948
5.28625
Table 5.2 - Observed Sample Display Times Statistics
96
The first few slides of any lecture are introductory
seconds while the median is 66 seconds.
The first few slides of any lecture are introductory
and
typically
time.
are
only
displayed
for
a
short
period
of
Some slides were viewed for a substantially longer
period of time when the
instructor was discussing specific
details of a particular slide.
On several occasions the instructor would flip back
to a slide already viewed.
In this case the display time
for a previously viewed slide was added to the display time
for the current slide occasionally resulting in relatively
long
view
times.
Data
was
collected
in
this
fashion,
because the actual design does not require a duplicate slide
to be sent when a previously displayed slide is requested.
The addition of this feature would add unnecessary detail to
the simulation model.
5.4.2
Probability Distributions
Probability models are fit to each data set, then
density graphs of possible density functions are compared
for similarity to the observed data.
The file size data may
be considered to be continuous and the histogram indicates
that the density function of the underlying distribution is
equally distributed about the center of the mean.
hypothesize that
a
normal
distribution is
We may
an appropriate
97
model
for
our
underlying
observed
distribution
data.
is
Similarly,
shifted
since
significantly
to
the
the
right, we may hypothesize that the Weibull distribution is
most similar to the display time histogram.
By means of an interactive procedure, UNIFIT creates
the
necessary
function.
parameters
for
each
selected
distribution
Several available probability models are fit to
each data set using the method of Maximum Likelihood (ML)
to estimate these parameters.
distribution
model
has
a
Each non-negative continuous
location
parameter
which
was
estimated using the method described by Zanakis [23].
The
location parameter is used to obtain the ML estimators for
the scale '|3' and shape 'cc parameters.
Selected parameters
for each distribution candidate for file sizes and display
times, may be seen in Table 5.3 and 5.4.
Once parameters are obtained for each distribution
function,
which
hypotheses
distribution
testing
function
is
performed
is
the
to
best
determine
choice
for
representing the observed data.
5.4.3
Hypotheses Testing
Hypotheses
distribution
to
testing
formally
is
performed
determine
on
whether
the
the
selected
fitted
distribution is a good representation of the observed data.
They test the following null hypothesis:
98
MODELS FOR SAMPLE : FILE SIZES
MODEL 1 : EXPONENTIAL DISTRIBUTION
LOCATION PARAMETER
2830.43
SCALE PARAMETER
2494.99
QUANTILE ESTIMATE
M.L. ESTIMATE
MODEL 2 : GAMMA DISTRIBUTION
LOCATION PARAMETER
SCALE PARAMETER
SHAPE PARAMETER
2830.43
1457.83
1.71144
QUANTILE ESTIMATE
M.L. ESTIMATE
M.L. ESTIMATE
MODEL 3 : LOGNORMAL DISTRIBUTION
LOCATION PARAMETER
2830.43
SCALE PARAMETER
7.50228
SHAPE PARAMETER
1.18925
QUANTILE ESTIMATE
M.L. ESTIMATE
M.L. ESTIMATE
MODEL 4 : WEIBULL DISTRIBUTION
LOCATION PARAMETER
2830.43
SCALE PARAMETER
2737.3
SHAPE PARAMETER
1.57639
QUANTILE ESTIMATE
M.L. ESTIMATE
M.L. ESTIMATE
MODEL 5 : NORMAL DISTRIBUTION
LOCATION PARAMETER
SCALE PARAMETER
M.L. ESTIMATE
M.L. ESTIMATE
5325.41
1471.67
MODEL 6 : UNIFORM DISTRIBUTION
LOWER ENDPOINT
2831.00
UPPER ENDPOINT
1.00920E+ 4
MODEL 7 : BETA DISTRIBUTION
LOWER ENDPOINT
UPPER ENDPOINT
SHAPE PARAMETER 1
SHAPE PARAMETER 2
0.
1.500E+ 4
8.42929
15.2820
M.L. ESTIMATE
M.L. ESTIMATE
DEFAULT
KNOWN
M.L. ESTIMATE
M.L. ESTIMATE
Table 5.3 - Model Parameters for File Size.
99
MODELS FOR SAMPLE : DISPLAY TIME
MODEL 1 : WEIBULL DISTRIBUTION
LOCATION PARAMETER
9.88789
SCALE PARAMETER
70.0318
SHAPE PARAMETER
1.34215
QUANTILE ESTIMATE
M.L. ESTIMATE
M.L. ESTIMATE
MODEL 2 : LOGNORMAL DISTRIBUTION
LOCATION PARAMETER
9.88789
SCALE PARAMETER
3.81387
SHAPE PARAMETER
1.07154
QUANTILE ESTIMATE
M.L. ESTIMATE
M.L. ESTIMATE
MODEL 3 : GAMMA DISTRIBUTION
LOCATION PARAMETE
SCALE PAR7USIETER
SHAPE PARAMETER
9.88789
41.0982
1,56766
QUANTILE ESTIMATE
M.L. ESTIMATE
M.L. ESTIMATE
MODEL 4 : EXPONENTIAL DISTRIBUTION
LOCATION PARAMETER
9.88789
SCALE PARAMETER
64.4279
QUANTILE ESTIMATE
M.L. ESTIMATE
MODEL 5 : NORMAL DISTRIBUTION
LOCATION PARAMETER
SCALE PARAMETER
M.L. ESTIMATE
M.L. ESTIMATE
MODEL 6 : BETA DISTRIBUTION
LOWER ENDPOINT
UPPER ENDPOINT
SHAPE PARAMETER 1
SHAPE PARAMETER 2
MODEL 7 : UNIFORM DISTRIBUTION
LOWER ENDPOINT
UPPER ENDPOINT
74.3158
48.5651
0.
1800.00
2.50646
58.1975
DEFAULT
KNOWN
M.L. ESTIMATE
M.L. ESTIMATE
10.0000
243.000
M.L. ESTIMATE
M.L. ESTIMATE
Table 5.4 - Model Parameters for Display Time
100
Ho; The Xj ^'s are random variables with
distribution function F.
This is called a goodness-of-fit test since it
determines
data.
how well the distribution "fits" the observed
If the null hypothesis Ho is not true, then we
assume that the following hypothesis H]^ is true:
H^:
The x's are not random variables with the
distribution function F.
The testing
comparison
Smirnov.
test
is
performed
statistics:
using the
chi-square,
following two
and
Kolmogorow-
[Intearvals are selected, for the chi-square test,
so that the expected proportion Pj of the Xj^'s that fall
into the
jth
interval are equal.
This stategy normally
results in unequal sized intervals.]
Tables 5.5 and 5.6 show the results of applying the
Chi-Square and Kolmogorov-Smirnov tests to the models.
For
both tests, the model test comparison with the file size
sample
closest
results
fit
in
for
the
both
normal
tests-
distribution
Figure
model
5.5
as
the
shows
the
density/histogram over plot with the normal function curve
and the files sizes depicted by the histogram.
The normal
function is used with the location and scale parameters in
Table 5.3 to create the following SIMSCRIPT statement for
file size:
LET SIZE(N.DISPLAY) =
NORMAL.F{5325-41, 1471.67, .SSEED) + -ADD.BITS
101
THE CHI-SQUARE GOODNESS-OF-FIT TEST HAVING 18 INTERVALS,
EACH WITH EQUAL MODEL PROBABILITY 5.55556E-2.
MODEL
DISTRIBUTION
CHI-SQUARE
KOLMOGOROV
-SMIRNOV
1
EXPONENTIAL
42.8000
.19040
2
GAMMA
24.4000
.13315
3
LOGNORMAL
73.2000
.17210
4
WEIBULL
20.4000
.11162
5
NORMAL
20.0000
.07276
6
UNIFORM
58.4000
.31214
7
BETA
22.0000
.09631
Table 5.5 - Hypotheses Test Comparisons for File Size.
102
THE CHI-SQUARE GOODNESS-OF-FIT TEST HAVING 15 INTERVALS,
EACH WITH EQUAL MODEL PROBABILITY 6.66667E-2.
MODEL
DISTRIBUTION
CHI-SQUARE
KOLMOGOROV
-SMIRNOV
1
WEIBULL
14.7895
.06562
2
LOGNORMAL
26.6316
.11995
3
GAMMA
15.1842
.06949
4
EXPONENTIAL
28.2105
.16287
5
NORMAL
22.6842
.11450
6
BETA
20.3158
.07823
7
UNIFORM
68.4737
.42291
Table 5.6 - Hypotheses test comparisions for display time.
11-1
103
10
9 -F
R
8 ••
E
7 •
Q
6
u
E
\
5 --
N
4 --
C
3 --
Y
2
- •
1
-•
\
i
\
/
J
o!o
Fl-ll
tI rS I nn,
7.5
5.0
SIZE (KB)
Density/Histogrcun Over Plot for File Sizes
2.5
Figure 5.5 -
8
F
R
E
7
6
Q
u
E
5
4
\
N
C
3
Y
2
\
V
1
240
60
120
180
DELAY TIME (SEC)
Figure 5.6 - Density/Historgram Over Plot for Display Times
0
104
Each display file is assigned a size in bits.
As
discussed in Section 5.5, the .ADD.BITS variable is used to
determine the performance effects on the system when the
entire function is shifted to the right.
Table 5.6 shows the model test comparison with the
display time sample.
The Weibull distribution is the best
fit according to both hypothesis tests.
Figure 5.5 shows
the density/histogram over plot with the Weibull curve and
the display times depicted by the histogram.
The respective
SIMSCRIPT statement for the display time is:
LET VIEW.TIME(N.DISPLAY) =
WEIBULL.F(1.34215, 70.0318, .VTSEED) - .SUB.TIME
The
1.34215
is
the
ML
estimate
for
the
shape
parameter and the 70.0318 is the ML estimate for the scale
parameter.
The .SUB.TIME variable is used in the following
section to determine the effects of shorter display times.
5.5 Simulation Tests and Results
Variations of the basic parameters were performed to
obtain
some
replication
potentially
of
a
useful
simulation
simulation
run,
is
results.
One
generally
not
sufficient to obtain an acceptable estimate of the system
performance.
A method is needed for ascertaining how close
an estimator is to the true measure.
The usual approach to
assessing the accuracy of an estimator is to construct a
105
confidence
interval
procedure
interval
approach
in
this
about
is
the
used
estimator.
to
performance
construct
evaluation.
A
sequential
a
confidence
A
sequential
procedure allows one to specify the relative precision of a
confidence interval.
The procedure assumes that
X2,...
is a sequence of random variables which need not be normal.
The
construct
a
specific
100(l-«)%
objective
of
confidence
the
procedure
interval
is
such that
to
the
relative precision is less than or equal to r for 0 < r < 1.
The ratio of the half-length to the magnitude of the sample
mean is the relative precision of the confidence interval.
A minimum number of replications of the run or ng is chosen
which satisfies that ng ^ 2 and let
6(n,oc) = t(n-i,i-oc/2)[s^(n)/n]l/2
be
the
half-length.
The
half-length
of
the
confidence
interval is added to or subtracted from the sample mean to
construct the confidence interval.
The sequential procedure
is as follows;
Step 0.
Make ng replications of the simulation and
set n — ng.
Step 1.
Compute the mean x(n) and half-length
S(n,a:) from
X2/ •.•/ Xj^.
Step 2. If [5(n,«)/[x(n)I] < r, then use,
= [x(n) - S(n,oc), X (n) + S{n,oc)]
as an approximate 100(!-«:)% confidence
interval for ji = E(x). Otherwise, replace n
by n+1 , make an additional replication, and
go to Step 1 [22].
106
In this simulation, a 90% confidence intervals are
obtained
minimum
with
at
number
Section 5.2,
of
least
a
10%
relative
replications
fx is
determined
ng
=
precision with
100.
As
noted
a
in
for the probability of the
expected nximber of: (1) files incorrectly displayed > 0, (2)
pictures not available for display > 0, and (3) files that
need retransmissions at the end of the lecture > 0.
The above sequential procedure
is
built
into the
simulation model within the REPEAT.RUNS process and is used
to terminate the simulation runs.
The number of independent
runs to achieve the required relative precision sometimes
reached
over
10,000
using
more than
30
CPU
hours
on
a
dedicated DEC MicroVax.
5.5.1
Transmission Protocol
The ntimber of times a file is sent ( .REPEAT.FILES)
is varied to verify that one should resend a file multiple
times to insure the file is received correctly.
The baud
rate parameter and BER was held constant at 9600 baud and 2
X lOE-05 respectively.
The value of 2 x lOE-05 for the BER
ic
is
choscn
bccciiioc
it
a
three-hold,
become unavailable for display.
point
showed
performance
that
under
a
poor
value
fileo
Runs were made with the
.REPEAT.FILES parameter set to from 1 to 5.
results
where
of
2
transmission
Simulation of
provided
the
conditions.
best
The
107
remainder of the tests were performed with this optimize
parameter.
5.5.2
This parameter is only optimum for this BER.
Bit Error Rates
Variations of the BER were carried out to obtain an
idea of how the system will perform under poor transmission
conditions.
varied.
A 9600 baud rate is maintained while the BER is
A threshold of about
Ix lOE-06 errors per bits
transmitted exists as shown in figure 5.7.
files
begin
to
be
displayed
At this point
incorrectly.
File
retransmissions are required at a 1 x lOE-03 BER as shown in
Figure 5.8.
The probability of incorrectly displayed and
retransmissions failures coincide with .33%
BER.
The
effect
of
poor
transmission
at 1 x 10E-03
lines
on
the
presentation has a significant effect between 1 x lOE-03 and
3 X
lOE-03 BER where approximately a 100% probability of
failure occurs.
5.5.3
Transmission Rate
The 9600 baud rate is evaluated under the slightly
sub-normal BER of 1 x lOE-06 bit errors/bits transmitted.
Simulation results confirm that a 9600 baud rate is more
than acceptable in the system design.
'Display Files not
Available' errors begin to occur between 1200 and 2400 baud.
108
Performance With Varying BER
0.Q4.
0.03 -
0.02 -
0.015
0.01
O.OOE-KJO
2.00E-+00
•
4.00E+00
6.0OE+OQ
(Times 10E-5)
Bit Error Rate
Inci^rrect Display
S.COE+C-O
I.OOE+OI
Figure 5.7 - BER Threshold for Incorrectly Displayed Files
109
Performance With Varying BER
0.3 -
0.2 0.18 -
0.16 0.14. 0.12 0.1
0.02 -
Bit Error Rate
•
Incorrect Disploy
+
Retransmissien
Figure 5.8 - BER Threshold for Files Requiring Retransmission
110
5.5.4
File Size
The
distribution
function
for
file
sizes
is
increased a constant amount to determine the threshold at
which problems occur in the design at the suggested 9600
baud rate.
Figure 5.9 shows that when files reach
50 KB
above the distribution function, 'Not Available for Display'
errors occur.
5.5.5
The mean file size is 5,325 bits.
Display Time
The distribution function for the display time is
reduced
by a constant amount by subtracting intervals of
time.
A two second
minimum
value is assumed.
Results
showed that at 9600 baud with an 1 x lOE-06 BER, decrements
in display time
generates
displayed correctly.
over 4,000
files all of which
This test indicates that thousands of
comparable sized support files may be added for transmission
without a degradation in system performance.
Ill
PERFORMANCE DUE TO FILE SIZE INCREASES
9600 Baud. 1 X 10E-06 BER
100
c
A
>
(0
o
c
o
ll.
I
o
z
160
Bn3 ABOVE SIZE FUNCTIOM (x 1 .OOOl
Lower Bound
+
Upper Bound
Figure 5.9 - System Performance Due to a Shift in File Sizes
CHAPTER 5
SUMMARY AND CONCLUSION
6.1
There
are
teleconferencing.
many
Smnmary
approaches
to
educational
A video broadcast with audio conference
provides the essential ingredients for a teleconference, yet
alone does not meet all teleconferencing requirements.
video
and
logistical
data
broadcast
nightmares
lacks interaction.
high
degree
with
audio
with course
conference
material
A
solves
delivery,
but
The data conference approach provides a
of
interaction,
yet
it
lacks
the
added
communication provided by the movements and gestures of the
presenter.
The ISDN
approach provides the communication
architecture for a high degree of interaction through data,
audio
and
available
video
conferencing.
shortly,
but
it
This
needs
to
technology
be
may
be
widespread
to
effectively reach all users.
The video and data broadcast with audio conferencing
is an intermediate step to the future ISDN on-demand service
of
full
motion
video
approach described
and
data
teleconferencing.
This
in the design section offers features
superior to those of existing system.
Supplemented by other
data network services such as facsimile, electronic mail,
file transfer and remote login, the video and data broadcast
112
approach
is
a
stepping
stone
to
future
technological
advances in teleconferencingThe
performance
evaluation
of
the
design
has
provided insight into design parameters which otherwise may
have
been
design.
missed
and
also
served
to
verify
the
system
The conferencing protocols for file transfer were
modified as a result of the performance parameters.
Sending
a file two consecutive times instead of one, three, or more
improved the performance on the number of slides available
for
display
Sending
when
three
high
files
bit
prior
error
to
the
rates
are
start
of
introduced.
the
resulted in a better overall system performance.
baud,
a
threshold
transmitted
exists
incorrectly.
are
not
of
about
when
2
files
x
lecture
At 9600
lOE-05
errors
per
bits
begin to
become
displayed
File sizes may reach up to 55 KB before files
available
for
display
at
the remote
site.
An
average display time over 2 seconds has little affect on the
performance of the system.
The
simulation
results
show
that
real
time
transmission of slides to local sites, at this time, is also
possible.
As higher resolution graphics packages are used,
file size increases will make real time transmission over
existing phpone lines impossible.
113
6.2
Cost Analysis
The cost of the system design can be divided up into
the control and remote site conferencing and transmission
components.
Appendix B shows a rough breakdown of required
equipment
and
development
its
is
estimated
required
to
costs.
integrate
Some
the
software
presentation
software with the Telecommunications Package at the Control
and Remote Sites.
6.3
Future
complexity
phases
to
the
Future Work
of
design
design,
but
modifications
may
between the student and instructor.
improve
will
add
interaction
Configuration of the
system to a full duplex mode could provide several added
benefits,
such
capability of
as
providing
querying the
remote
students
with
the
instructor during the lecture
through their terminals.
Limited file transfer through the data portion of
the voice/data channel could allow added
design.
with
Real-time
the
design
integration of
might
also
features to the
electronic
improve
scratch pad
the
presentation
microwave
transmission
features.
Both
the
satellite
and
systems in the existing system have sufficient bandwidth for
expansion to higher data rates.
114
Additional bandwidth is
115
subcarrier modulators, demodulators and power supplies at
the transmit and receive end.
A higher bandwidth approach
could allow for the use of higher resolution graphics Additional research
is
needed
based grading of homework and tests.
in the area of AI
Also exploration of
the ISDN architecture of the 5ESS switch is necessary to
pursue the design of the next generation teleconferencing
systems.
APPENDIX A
' SIMSCRIPT II.5 SOURCE PROGRAM FOR SIMULATION
VIDEO AND DATA CONFERENCE SIMULATION
PREAMBLE
PROCESSES INCLUDE GENERATOR, TRANSMIT.AND.DISPLAY,
RECEIVE.AND.DISPLAY, REPEAT.RUNS
DEFINE TERM.BUFFER, FILE,STATUS, N.DISPLAY.CORRECT
N. DISPLAY. INCORRECT,N.DISPLAY, N.RETRANS
N.FILES,
N.NOT.AVAILABLE.DISPLAY,
COMMAND
E N D.P R E S E N T A T I O N , S E N D . F I L E
CURRENT.DISPLAY,RECEIVE.BUFFER.INDICATION,
END.OF.PRESENTATION, SEND-FILE.INDEX, N.CYCLED
RECEIVE.DISPLAY,N.RUNS, INCORRECT, NOTAVAIL,
RETRANS, AMOUNT.NOTAVAIL, AMOUNT.RETRANS
AMOUNT-INCORRECT AS INTEGER VARIABLES
PERMANENT ENTITIES
EVERY FILE
HAS A VIEW-TIME
AND A SIZE
AND A N-TRANSMIT
AND A R-QUALITY
DEFINE VIEW.TIME, SIZE, N.TRANSMIT, AND R.QUALITY
AS INTEGER VARIABLES
DEFINE
DEFINE
DEFINE
DEFINE
DEFINE
DEFINE
DEFINE
DEFINE
DEFINE
DEFINE
DEFINE
.BER TO MEAN 1 / 1000000
.SERIAL.RATE TO MEAN 9600
.ADD.BITS TO MEAN 0
.SUB.TIME TO MEAN 120
.REPEAT.FILES TO MEAN 3
.REPEAT.HEADER TO MEAN 3
.MAXFILES TO MEAN 10000
-SIZE.COMMAND.MSG TO MEAN 32 ''BITS
.LECTURE.PERIOD TO MEAN 75 * 60 "SECONDS
-N-SUPPORT.FILES TO MEAN 0
-N.FILES.AHEAD TO MEAN 7
115
117
DEFINE .SSEED TO MEAN 5
DEFINE .VTSEED TO MEAN 5
DEFINE .ESEED TO MEAN 7
DEFINE .T TO MEAN 1.660 " T
CONFIDENCE
INFINITY
WITH
90%
DEFINE .GAMMA TO MEAN .10 "REALATIVE PRECISION
''THRESHOLD
DEFINE TRUE TO MEAN 1
DEFINE ESCAPE TO MEAN 1
DEFINE ON TO MEAN 1
DEFINE FULL TO MEAN 1
DEFINE OFF TO MEAN 0
DEFINE EMPTY TO MEAN 0
DEFINE FALSE TO MEAN 0
DEFINE DISPLAY TO MEAN 4
DEFINE END.PRESENTATION TO MEAN 5
DEFINE FILE.SEND TO MEAN 6
DEFINE .GOOD.COPY TO MEAN 2
DEFINE .BAD.COPY TO MEAN 1
DEFINE SEND.A.DISPLAY.COMMAND TO MEAN SEND.COMMAND
DEFINE SEND.A.HEADER.COMMAND TO MEAN SEND.COMMAND
DEFINE SEND.A.FINISHED.COMMAND TO MEAN SEND.COMMAND
TALLY INCORRECT.VAR AS VARIANCE, INCORRECT.MEAN AS
MEAN OF INCORRECT
TALLY NOTAVAIL.VAR AS
MEAN OF NOTAVAIL
VARIANCE,
NOTAVAIL.MEAN
AS
TALLY RETRANS.VAR AS VARIANCE, RETRANS.MEAN AS MEAN
OF RETRANS
TALLY
AMOUNT.INCORRECT.MEAN
AS
MEAN
OF
AMOUNT.INCORRECT
TALLY
A M O U N T . N O T A V A I L.M E A N
AS
MEAN
OF
AMOUNT.NOTAVAIL
TALLY AMOUNT.RETRANS.MEAN AS MEAN OF AMOUNT.RETRANS
END
"PREAMBLE
118
MAIN
ACTIVATE A REPEAT.RUNS NOW
START SIMULATION
END ''MAIN
PROCESS REPEAT.RUNS
UNTIL(
(
(RETRANS.PRECISION <= .GAMMA)
(INCORRECT.PRECISION <= .GAMMA) AND
(NOTAVAIL.PRECISION <= .GAMMA)
AND
)
(
AND
(RETRANS.MEAN > 0) OR
(INCORRECT.MEAN > 0) OR
(NOTAVAIL.MEAN > 0) OR
(N.RUNS > 300) " NO OCCURANCES
)
AND
(N.RUNS > 100) ''PREVENT PREMATURE STOPS
)
OR
N.RUNS = 10000 "PREVENT ENDLESS RUN
LET
LET
LET
LET
N.RETRANS = 0
N.DISPLAY.INCORRECT = 0
N.DISPLAY.CORRECT = 0
N.NOT.AVAILABLE.DISPLAY = 0
PERFORM INITIALIZE
ACTIVATE A RECEIVE.AND.DISPLAY NOW
ACTIVATE A TRANSMIT.AND.DISPLAY NOW
SUSPEND
ADD 1 TO N.RUNS
IF N.DISPLAY.INCORRECT > 0
LET INCORRECT = TRUE
LET AMOUNT.INCORRECT = N.DISPLAY. INCORRECT
ELSE
LET INCORRECT = 0
ALWAYS
119
IF N.NOT.AVAILABLE.DISPLAY > 0
LET NOTAVAIL = TRUE
L E T
A M O U N T . N O T A V A I L
N.NOT.AVAILABLE - DISPLAY
ELSE
LET NOTAVAIL = 0
ALWAYS
IF N.RETRANS > 0
LET RETRANS = TRUE
LET AMOUNT.RETRANS = N.RETRANS
ELSE
LET RETRANS = 0
ALWAYS
IF INCORRECT.MEAN > 0
LET INCORRECT.PRECISION =
(.T * SQRT.F{INCORRECT.VAR / N.RUNS))/
INCORRECT.MEAN
ALWAYS
IF NOTAVAIL.MEAN > 0
LET NOTAVAIL.PRECISION =
(.T * SQRT.F{NOTAVAIL.VAR / N.RUNS)) /
NOTAVAIL.MEAN
ALWAYS
IF RETRANS.MEAN > 0
LET RETRANS.PRECISION =
(.T * SQRT.F(RETRANS.VAR /N.RUNS))/
RETRANS.MEAN
ALWAYS
LOOP
PRINT 13 LINES WITH .GAMMA * 100,
(INCORRECT.MEAN
INCORRECT.PRECISION
*
INCORRECT.MEANjl),
(INCORRECT.MEAN
+
INCORRECT.PRECISION
*
INCORRECT.MEAN/2),
NOTAVAIL.PRECIS ION
*
(NOTAVAIL.MEAN
NOTAVAIL.MEAN/2),
(NOTAVAIL.MEAN
+
NOTAVAIL.PRECISION
*
NOTAVAIL.MEAN/2),
(RETRANS.MEAN - RETRANS.PRECISION * RETRANS.MEAN/2),
(RETRANS.MEAN + RETRANS.PRECISION * RETRANS.MEAN/2),
N.RUNS, .BER, .SERIAL.RATE, .REPEAT.FILES,
.ADD.BITS, .SUB.TIME, AMOUNT.NOTAVAIL.MEAN,
AMOUNT.INCORRECT.MEAN, AMOUNT.RETRANS.MEAN
120
90%
THUS
CONFIDENCE INTERVAL ESTIMATES
RELATIVE PRECISION
P(INCORRECTLY DISPLAYED SLIDES
>0)
WITH
LESS
IS [
* * *
THAN
***
%
* * * *
•
/
*** ^ **** J
P(SLIDES NOT AVAILABLE FOR DISPLAY > 0)
Jg
^
***^****
P(NUMBER SLIDES NEED RETRANSMISSION > 0)
IS [
*** ^ **** J
***,****
*** ^ **** J
jg
NUMBER OF RUNS
BIT ERROR RATE
IS
*****
DATA RATE
IS
Jg
****
NUMBER REPEAT FILES
Jg
*********
+ BITS TO FILES
* * * * *
- TIME TO DISPLAY IS
MEAN OF OCCURANCE: NOTAVAIL=**.****
RETRANS=**.***
INCORRECT=**.***
PRINT 9 LINES WITH N.RUNS, N.DISPLAY, N.RETRANS,
N.DISPLAY.CORRECT, N.DISPLAY.INCORRECT,
N.NOT.AVAILABLE.DISPLAY, NOTAVAIL.PRECISION,
• GAMMA, NOTAVAIL.MEAN, NOTAVAIL.VAR,
INCORRECT.PRECISION, .GAMMA, INCORRECT.MEAN,
INCORRECT.VAR, RETRANS.PRECISION, .GAMMA,
R E T R A N S . V A R ,
R E T R A N S . M E A N ,
AMOUNT.NOTAVAIL.MEAN,
AMOUNT.INCORRECT.MEAN, AMOUNT.RETRANS.MEAN
THUS
RUNS=**** N.DISPLAY=***
B.DISPLAY=*** NOTAVAIL=***
VARIABLE
VARIANCE
SAMPLE PRECISION
NOT AVAIL
*.**** <
INCORRECT
*,**** <
RETRANSMIT
*,**** <
MEAN OF OCCURANCE:
RETRANS=**.***
END "REPEAT.RUNS
RETRANS=***
SAMPLE MEAN
***^*****
***^*****
***^*****
NOTAVAIL=**.***
G.DISPLAY=***
SAMPLE
*^****
*^****
*,****
INCORRECT=**.***
121
r r
———
———-
-
ROUTINE INITIALIZE
r r
DEFINE DISPLAY.TIME, I AS INTEGER VARIABLES
DEFINE V.TIME, F.SIZE AS INTEGER VARIABLES
LET
LET
LET
LET
END.OF.PRESENTATION = FALSE
SEND.FILE.INDEX = 1
DISPLAY.TIME = 0
N.DISPLAY =0
CREATE EVERY FILE {.MAXFILES)
UNTIL DISPLAY.TIME > .LECTURE.PERIOD
DO
ADD 1 TO N.DISPLAY
LET VIEW.TIME(N.DISPLAY) =
WEIBULL.F(l.34215,. 70.0318,
.SUB.TIME
IF VIEW.TIME(N.DISPLAY) < 2
LET VIEW.TIME(N.DISPLAY) = 2
ALWAYS
LET SIZE(N.DISPLAY) =
NORMAL.F(5325.41,
.ADD.BITS
1471.67,
.vtseed)
-
.sseed)
+
IF SIZE(N.DISPLAY) < 2000
LET SIZE(N.DISPLAY) = 2000
ALWAYS
ADD VIEW.TIME(N.DISPLAY) TO DISPLAY.TIME
LOOP
LET
FOR
N.DISPLAY
=
N.DISPLAY
I = (1 + N.DISPLAY)
.N.SUPPORT.FILES )
-1 "DONT GO OVER
''LECTURE.PERIOD
TO ( 1 + N.DISPLAY +
DO
LET SIZE(I) = 5400
LOOP
LET N.FILES = .N.SUPPORT.FILES + N.DISPLAY
END "INITIALIZE
122
PROCESS GENERATOR
END
FOR CURRENT.DISPLAY =1 TO N.DISPLAY
DO
LET TERM.BUFFER = FULL
WAIT ( VIEW.TIME(CURRENT.DISPLAY)
MINUTES
LOOP
LET END.OF.PRESENTATION = TRUE
"GENERATOR
/
60
)
PROCESS TRANSMIT.AND.DISPLAY
DEFINE T AS INTEGER VARIABLE
FOR T=1 TO .REPEAT.HEADER
DO
PERFORM SEND.A.HEADER.COMMAND
RESUME RECEIVE.AND.DISPLAY
LOOP
FOR T =1 TO ( .N.FILES.AHEAD * .REPEAT.FILES)
DO
PERFORM SEND.A.FILE
RESUME RECEIVE-AND-DISPLAY
LOOP
ACTIVATE A GENERATOR NOW
"BEGIN DISPLAYING
LET END.OF.PRESENTATION = FALSE
UNTIL END.OF.PRESENTATION = TRUE '' SET BY GENERATOR
DO
IF TERM.BUFFER = EMPTY
PERFORM SEND.A.FILE
RESUME RECEIVE.AND-DISPLAY
ELSE
LET TERM.BUFFER = EMPTY
RECEIVE.DISPLAY = CURRENT.DISPLAY
PERFORM SEND.COMMAND
LET COMMAND = DISPLAY
RESUME RECEIVE.AND.DISPLAY
ALWAYS
LOOP
DO
PERFORM SEND.COMMAND
LET COMMAND = END.PRESENTATION
RESUME RECEIVE.AND.DISPLAY
END ''TRANSMIT.AND.DISPLAY
123
ROUTINE SEND.COMMAND
WAIT
((.SIZE.COMMAND.MSG
/
.SERIAL.RATE)
/60
)
MINUTES
LET RECEIVE.BUFFER.INDICATION = ON
END ''SEND.COMMAND
r t
^
:
— —r — rr:
::
\
r——7^
r
ROUTINE SEND.A.FILE
PERFORM DETERMINE.NEXT.FILE
WAIT ((SIZE(SEND.FILE.INDEX) / - SERIAL.RATE) /60 )
MINUTES
LET RECEIVE.BUFFER.INDICATION = ON
LET COMMAND = FILE.SEND
END "SEND.A.FILE
r r
ROUTINE DETERMINE.NEXT.FILE
9 r
;
IF
(CURRENT.DISPLAY < SEND.FILE.INDEX) OR (
SEND.FILE.INDEX = 0)
IF N.TRANSMIT(SEND.FILE.INDEX) < .REPEAT.FILES
ADD 1 TO N.TRANSMIT(SEND.FILE.INDEX)
ELSE
ADD 1 TO SEND.FILE.INDEX
IF SEND.FILE.INDEX > N.FILES
LET SEND.FILE.INDEX = 1
ADD 1 TO N.CYCLED
ALWAYS
N.TRANSMIT(SEND.FILE.INDEX) = 1
ALWAYS
ELSE
IF CURRENT.DISPLAY = N.DISPLAY
IF
N.TRANSMIT(SEND.FILE.INDEX)
<
.REPEAT.FILES
ADD 1 TO N.TRANSMIT(SEND.FILE-INDEX)
ELSE
ADD 1 TO SEND.FILE.INDEX
IF SEND.FILE.INDEX > N.FILES
LET SEND.FILE.INDEX = 1
ADD 1 TO N.CYCLED
ALWAYS
N.TRANSMIT(SEND.FILE.INDEX) = 1
ALWAYS
ELSE IF N.CYCLED > 0
124
IF
N.TRANSMIT{SEND.FILE.INDEX)
<
.REPEAT.FILES
ADD 1 TO N.TRANSMIT(SEND.FILE.INDEX)
ELSE
ADD 1 TO SEND.FILE.INDEX
IF SEND.FILE.INDEX > N.FILES
LET SEND.FILE.INDEX = 1
ADD 1 TO N.CYCLED
ALWAYS
N.TRANSMIT(SEND.FILE.INDEX) = 1
ALWAYS
ELSE
LET SEND.FILE.INDEX = CURRENT.DISPLAY + 1
N.TRANSMIT(SEND.FILE.INDEX) = 1
ALWAYS
ALWAYS
ALWAYS
END ''DETERMINE.NEXT.FILE
PROCESS RECEIVE.AND.DISPLAY
DEFINE END.OF.RECEPTION, LAST.DISPLAY AND
LOCAL.TERM.BUFFER AS INTEGER VARIABLES
UNTIL END.OF.RECEPTION = TRUE
DO
SUSPEND
''WAIT FOR COMMANDS FORM CONTROL SITE
IF RECEIVE.BUFFER.INDICATION = ON
IF COMMAND = FILE.SEND
PERFORM CHECK.FOR.ERRORS
I F
F I L E . S T A T U S
>
R.QUALITY(SEND.FILE.INDEX)
"SAVE THE FILE
R.QUALITY(SEND.FILE.INDEX) =
FILE.STATUS
ALWAYS
ELSE
IF COMMAND = DISPLAY
ADD (RECEIVE.DISPLAY - LAST.DISPLAY -1) TO
N.NOT.AVAILABLE.DISPLAY
LET LAST.DISPLAY = FiECEIVE.DISPLAY
IF R.QUALITY(RECEIVE.DISPLAY) = .GOOD.COPY
''DISPLAY IT
ADD 1 TO N.DISPLAY.CORRECT
ELSE IF R.QUALITY{RECEIVE.DISPLAY) =
.BAD.COPY
''DISPLAY IT
125
ADD 1 TO N.DISPLAY.INCORRECT
ELSE
ADD 1 TO N.NOT.AVAILABLE.DISPLAY
ALWAYS
ALWAYS
ELSE
IF COMMAND = END.PRESENTATION
LET END.OF.RECEPTION = TRUE
ADD (N.DISPLAY - LAST.DISPLAY) TO
N.NOT.AVAILABLE.DISPLAY
ALWAYS
ALWAYS
ALWAYS
LET RECEIVE.BUFFER.INDICATION = OFF
ALWAYS
LOOP
PERFORM CHECK.RETRANS
RESUME REPEAT.RUNS
END "RECEIVE.AND.DISPLAY
ROUTINE CHECK-FOR.ERRORS
IF
(1 - -BER)**(SIZE(SEND.FILE.INDEX))
RANDOM.F{.eseed)
FILE.STATUS = .BAD.COPY
ELSE
FILE.STATUS = .GOOD.COPY
ALWAYS
END ''CHECK.FOR-ERRORS
ROUTINE CHECK.RETRANS
r r
DEFINE II AS INTEGER VARIABLE
LET N.RETRANS = 0
FOR II = 1 TO N.FILES
DO
IF R.QUALITY(II) NE .GOOD.COPY
ADD 1 TO N.RETRANS
ALWAYS
LOOP
END ''CHECK.RETRANS
<
APPENDIX B
EQUIPMENT LIST AND APPROXIMATE COSTS
Control Site
A.
Additions for NTSC Encoded Computer
Graphics.
Computer
IBM Model 50 (PS-2/50)
-80286 processor, 30 MB HD,
1 MB RAM, 1 High Density Floppy.
$2,715
CGA Graphics Card and Monitor
$
404
Mouse
$
65
Cart
$
175
$
238
Software
IBM Storyboard Plus
NTSC Encoder
Shintron
CBIOO-EN
$1,390
Shintron Line Converter CBIOO-LC
$
290
Line Switch
$
100
$
252
$
75
Video Distribution Amplifier
Sigma
VDA-IOOA
Misc. cables and connectors
$ 5,704
B.
Additions for Data Broadcast.
Conference Facility
Software
Integrated Presentation Package
(Development Costs)
126
$ 4,000
127
Hardware
Panasonic PTlOlN/PT-301 Color
Video Projection System
Image Scanner, Dest PC Scan 2020
(optional)
$6,900
$ 3,000
Transmission Facility
Quoriim Audio-Graphic Teleconferencing
Bridge plus associated telephone lines $26,000
Voice/Data Modems with 2400 baud
data ( 1 Per Local Remote Conference
location)
$2,500
Digital to Analog Converters and
Associated Communications Electronics
II.
$3,500
REMOTE SITE
A.
Additions for NTSC Encoded Computer
Graphics.
NONE
B.
$0.00
Additions for Data Broadcast
Workstation Components
Computer
IBM Model 50 (PS-2/50)
-80286 processor, 30 MB HD,
1 MB RAM, 1 High Density Floppy.
$2,715
CGA Graphics Card and Monitor
$
404
Barcodata PC Video Projection
System ( CGA/EGA Compatible)
$10,495
Image Scanner, Dest PC Scan 2020
(optional)
$3,000
Laser Printer
$ 4,000
Cart
Software
$
175
128
Developmental Presentation Package
$ 2,000
Bulletin Board System (Shareware)
$
0
Reception Facility
1) Long Haul Remote Sites
Analog to Digital converters and
associated electronics equipment
$ 2,500
2) Local Remote Sites
Voice/Data Modem with high
speed data only option.
$ 2500
REFERENCES
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New York:
McGraw-
[3] Benson, K. B.
Television Engineering Handbook.
York: McGraw-Hill, 1985.
New
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"Integrated
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IEEE
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130
[13] Gecsei, J. The Architecture of Videotex Systems, New
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"BBS Software", Info World,
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"Telematic Services and
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Modeling and Analysis, New York:
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McGraw-Hill,
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[23]
Law, Averill M-, Vincent, Stephen G.
UNIFIT An
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"Research Computer Netwrks and Their
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[25]
Microwave Video Radio, Instruction Book.
Transmission Systems Division, Rockwell
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131
International Dallas, Texas 1983.
[26] National Technological University, Operational
Procedures Manual, Fort Collins, CO
Revision
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[27]
National Technological University,
Statistics,
Fort Collins, CO: 1987.
Sawuak
Card
[28] Nussbaum, Eric, Noller, W. E., "Integrated Network
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and
ISDN",
IEEE
Communications Magazine, Vol. 24, No.3 (March
1986).
[29] Roberts, R. S. Television Engineering Broadcast,
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