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III DEFENSE COMMUNICATION SYSTEM
FROM
CHRISTIAN ROVSING A/S
C. COMMERCIAL
CCIS CASE HISTORY
VIDEOTEX
V̲I̲D̲E̲O̲T̲E̲X̲
1. O̲B̲J̲E̲C̲T̲I̲V̲E̲
VIDEOTEX is the name given to a low cost, easy to use,
two way information service for homes, offices, libraries,
schools, railway terminals, etc. The main objective
of VIDEOTEX is to provide subscribers with information
- text and graphics - at an ordinary TV console.
Information provided to subscribers is to come from
a VIDEOTEX Computer Center (VCC) data base maintained
by participating suppliers of information. Information
can be updated in several ways:
o on-line immediate edit - supplier determines when
to update
o on-line bulk edit - supplier can transmit new data
to VCC at any time, VCC updates at scheduled times
o off-line magnetic tape transfer - VCC updates at
scheduled times
o direct connection through VCC between subscribers
and suppliers.
A subscriber establishes a two-way information session
via common carrier switched lines by dialing VCC. If
an input port is available, VCC accepts the call request
and gives access rights.If a call request cannot be
accepted, the subscribed receives a busy tone - as
in normal telephone usage.
A subscriber can also transmit a message to other subscribers
or suppliers of information. Finally, interactive services
between a subscriber and the VCC can be provided.
It should be noted that the individual subscriber does
not necessarily have access to all services available,
but rather to the services agreed upon; this results
in lower costs when a lesser level of service is required.
2. B̲E̲N̲E̲F̲I̲T̲S̲
VIDEOTEX technology offers the possibility of electronic
information distribution to subscribers at costs competitive
with classical informtion distribution media in use
today.
Major advntages of VIDEOTEX lie in its convenience
and accessibility to up-to-date informtion using normal
TV consoles as terminals and common carrier lines for
tranmsmission.
Information search is easy to carry out, and use of
both primary and secondary keywords effects one-command
informtion retrieval.
As VIDEOTEX is designed with internationally agreed
upon layers of software, future expansion of system
function can be achieved by simply adding functional
modules.
3. S̲Y̲S̲T̲E̲M̲ ̲F̲U̲N̲C̲T̲I̲O̲N̲S̲
The principal functions offered by VIDEOTEX are:
- Information Retrieval
- Message Service
- On-line Applications
- Transaction Service
- Closed User Groups
- On-line Editing
In the sub-sections to follow, each principal function
is outlined.
I̲N̲F̲O̲R̲M̲A̲T̲I̲O̲N̲ ̲R̲E̲T̲R̲I̲E̲V̲A̲L̲
By using this function, a subscriber selects display
of information - one screen image (frame) at a time
- from a wide choice of possibilities. Selection of
frames is via a key pad (numeric keys plus a few special
keys) or keyboard (alphanumeric and special keys),
and three methods of selection are provided:
1. Hierarchical Search - based on "menuframes", each
allowing the subscriber to choose the desired continuation
frame and thus refine a choice until the required
information is at hand.
2. Direct Page Choice - each page in the data base
(a page can include one or more image frames) is
identified by a page number of 1 to 14 digits;
a subscriber enters a page number and the first
image frame in that page is displayed; remaining
frames can be viewed sequentially.
3. Keyword Search - a disc resident subject index
converts keywords to page numbers.
M̲E̲S̲S̲A̲G̲E̲ ̲S̲E̲R̲V̲I̲C̲E̲
Facilities for transmitting messages from one subscriber/supplier
(user) to another subscriber/supplier are provided.
Users are notified of awaiting messages upon log-in
to the system.
O̲N̲-̲L̲I̲N̲E̲ ̲A̲P̲P̲L̲I̲C̲A̲T̲I̲O̲N̲ ̲S̲E̲R̲V̲I̲C̲E̲
This function provides data processing at VCC under
user control. Dedicated page numbers are associated
with applications, and frames used in these applications
contain formatted input/output fields.
T̲R̲A̲N̲S̲A̲C̲T̲I̲O̲N̲ ̲S̲E̲R̲V̲I̲C̲E̲
Pre-formatted forms can be filled in by the user and
returned to the originator.
C̲L̲O̲S̲E̲D̲ ̲U̲S̲E̲R̲ ̲G̲R̲O̲U̲P̲S̲
Access to specific areas of the data base is available
only to authorized members of a "Closed User Group".
There can be more than one closed user group, and users
may be authorized as members of more than one group.
O̲N̲-̲L̲I̲N̲E̲ ̲E̲D̲I̲T̲I̲N̲G̲
Suppliers of information can edit frames of information
on-line, i.e change frames without delays. This necessitates
an extended alphanumeric (editing) keyboard interfaced
to a modified TV console.
4. E̲Q̲U̲I̲P̲M̲E̲N̲T̲ ̲D̲E̲S̲I̲G̲N̲
An overview of the hardware structure is given in fig.1,
and the principal components are:
- VIDEOTEX Retrieval Unit
- VIDEOTEX Database Unit
- VIDEOTEX Input Unit
- VIDEOTEX Ex Database Unit
Each unit is a self-contained, operational computer
system and dedicated to specific sub-tasks. Interchange
of information between units is via the TDX-Bus, a
time division multiplex path with high bandwidth.
In the subsections to follow the principal hardware
units are described.
R̲e̲t̲r̲i̲e̲v̲a̲l̲ ̲U̲n̲i̲t̲
Each VIDEOTEX Retrieval Unit (VRU) is a self-contained
computer system whose hardware/software controls the
user dialogue and each VRU has 80 ports. In addition,
each VRU is equipped with one moving head disc containing
80M Bytes and one fixed head disc containing 5M Bytes.
Figure 1
TITLE "MAJOR POINT"
The 80M Byte VRU disc can contain approximtely 30,000
frames (screen images) of information - assuming 1400
Bytes/frame. This number of frames should be adequate,
as experience shows that only 10% of all possible frames
are used in 90% of demands for information. Should
a frame to be displayed not be found on the VRU disc,
a request is sent to the VIDEOTEX database, and a data
transfer is effected. If space is available on the
80MB disc, the new frame is kept; if space is not available,
the new frame replaces one that is less likely to be
called.
The 5MB fixed disc contains standard frames of VCC,
log-on frames, message service frames, etc. Also stored
here is the primary keyword index. Additionally this
disc is used as a session allocated virtual memory
resource to gather statistics and accounting information.
V̲i̲d̲e̲o̲t̲e̲x̲ ̲D̲a̲t̲a̲b̲a̲s̲e̲ ̲U̲n̲i̲t̲
The VIDEOTEX Data B̲ase U̲nit (VBU) is a self-contained
computer system containing hardware/software to control
and maintain an internal database. The VBU is dualized
as it is a mandatory function of VIDEOTEX. Therefore,
the VIDEOTEX configuration contains 2 VBU's - one acting
as a back-up for the other. Thus it is possible to
reestablish the data base if one of the disc drives
crashed.
V̲i̲d̲e̲o̲t̲e̲x̲ ̲I̲n̲p̲u̲t̲ ̲U̲n̲i̲t̲
The VIEDOTEX Input Unit (VIU) is a selfcontained, operational
computer system containing hardware and software to
input data from information suppliers to the Videotex
system.
The VIU also provides facilities for editing of information.
Input and editing is provided either as bulk transfer
or as on-line editing.
Bulk transfer is provided either by means of Magnetic
Tape input or by means of bulk updating from a remote
off-line microprocessor-based intelligent editing terminal.
On-line editing is provided as an interactive application
service available to information suppliers having business
or residential terminals equipped with an edition keyboard.
There are 44 ports allocated for input. Of these, 8
ports are used for remote VIDEOTEX bulk-updating and
36 ports for on-line editing.
E̲x̲D̲B̲ ̲I̲/̲F̲ ̲U̲n̲i̲t̲
The VIDEOTEX ExDB I/F Unit (VEU) is a self-contained,
operational microprocessor providing 4 external database
lines to the VIDEOTEX System.
Available I/F protocols are:
- IBM 2780 BSC
- HDLC/X.25
- HDLC
- SDLC/SNA (3276, 3270
datastream compatible)
5. E̲X̲P̲A̲N̲D̲A̲B̲I̲L̲I̲T̲Y̲
The VIDEOTEX System Architecture (VSA) developed by
Christian Rovsing A/S is based on a comprehensive and
flexible approach; the system contains a number of
operational capabilities performed by distributed processing
elements which together provide the desired VIDEOTEX
Service.
Each processing element communications with other operational
elements through a transmission network (e.g. X25 package
switching network, local area network, TDX-bus etc.)
System growth and expansion is, in virtue of the distributed
architecture, very flexible, and in fact the growth
potential is only a question of network capacity.
