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THE INS AND OUTS
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OF
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PACKET SWITCHING
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by:
The Seker
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Tribunal of Knowledge!
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Written (c) June 23, 1986
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'TRIBUNAL COMMUNICATIONS LTD'
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Not many people are quite aware how complex packet switched networks
are.
In this file I hope to clear up all confusion and answer all questions
concerning packet switching and making international datacalls via packet
switched networks.
HISTORY
=======
Using normal phone lines, computers can only transmit data at speeds
up to
1200 bps efficiently. This is very slow compared to the inner workings
of even
the slowest computer. If computers could transmit across phone lines at
higher
speeds, 9600 bps for example, there would still be the problem of using a
compatible protocol. Packet switched networks take care of these and
other
problems dealing with communications.
The idea of developing a completely computerized network for
computers was
first discussed in the mid 1960's..probably someplace like Bell Labs,
MIT, or
the like. But it wasn't until a decade later that the theory was put
into
construction.
The first packet network was a project of the Defense Department.
They
labeled it ArpaNet. It was and still is a boon for advanced hackers, as
it is
host to over 300 government related computers. (See 'Hacking ArpaNet'
written
by the Wizard of ArpaNet for an indepth look at breaching this system.)
Today there are over five commercial packet networks in the United
States
alone (Telenet, Tymnet, CompuServe, etc), and many more throughout the
world.
HOW IT WORKS
============
In essence, packet switching services operate at 4800 bps full
duplex
(both direction simulstaneously) and use a form of TDM (Time Division
Multiplexing), a transmission which is basis for most of the world's
voice
communications. Transmission streams are separated into convenient sized
blocks or 'packets', each one of which contains a head and tail
signifying the
origination and destination of the data. The packets are assembled by
either
the originating system or by a special facility supplied by the packet
switch
system. Packets in a single transmission may follow the same physical
path
(same cable) or may use an alternate route (ie. a detour cable) depending
on
the congestion of the system. The packets from one 'conversation' are
very
likely to be interleaved with packets from other 'conversations'. The
originating and receiving computers see none of this mixing. At the
receiving
end, the various packets are stripped of their routing information, and
re-assembled in correct order before presentation to the computer
terminal.
All public networks that use packet switching have installed a
standard
protocall to try and be compatible with each other. (good luck) The
standard,
which is called CCITT X.25 (Developed at the Geneva conferences.), is
implemented on all international datacalls. This is a complex system for
interface between data terminal equipment and data circuit-terminating
equipment.
ACCESSING
=========
Users (hackers) can access packet switching in a variety of ways.
Special
terminals called Packet Terminals, which are usually hard wired to the
nearest
PSS (Packet Switch Stream), that are able to create and arrange data into
the
correct format are often used. This is very expensive, a reason why you
will
only be likely to see these type of terminals within large company office
buildings. The average person will probably access a packet network
using an
ordinary ascii terminal (computer and modem), and connect to a special
PSS
facility called a PAD (Packet Assembler/Disassembler) which will handle
the
formatting for them.
USING
=====
To use a public packet network it is usually required for one to
have a
NUI (Network User Identity) which is registered at your local PSE (Packet
Switch Exchange) for billing purposes...or a way around this.
Dial into your local PAD (often called port) and enter your NUI. If
a
valid ID is not given, the port will usually throw you off. (There are a
few
exceptions which we will discuss later.) Then one enters the NUA
(Network User
Address) or call name of the computer he/she wants to access. Each
computer on
a network has one given to them. This is usually in the form of numbers
or
somtimes letters. (As in Tymnet's case.) After the correct information
is
entered, the network will connect you via its private sattelite system to
the
local phone system of your destination and then onto the computer you
wish
to access.
BILLING
=======
Billing on networks is done to either the user or reversed and
charged to
the designated computer. Charging is not done according to the distance
of the
call or by the time passed, rather by how many packets exchanged and
sometimes
a small fee for CPU (Centeral Processing Unit) time.
Many packet networks do not require you to have an NUI at all. One
of
these that many of you probably have worked with is Telenet. It is a
leading
public network throughout the continent. Billing on there is a variation
of
the norm. There is only a charge to a user when he/she wants to access a
computer internationally or one which doesn't accept the charges of the
datacall. (ie. REFUSE COLLECT CONNECT 00 AA) Billing like this will
probably
disappear soon due to the greed of big business.
INTERNATIONAL DATACALLS
=======================
If a person wishes to call a computer located on a foreign network,
there
is a little procedure which must be done. As I said earlier, each
computer on
a network has its own address. (NUA) Networks also have their own
'address',
which is called a DNIC. (Data Network Identification Code) This code is
four
numerical digits long. The first three numbers in this code represent
which
country the network is located in. The fourth digit is which service in
that
particuliar country, as some countries have more than one network. (For
example, 5052 is Australia's Auspac DNIC. 505 is the country code. 2 is
the
service code.) A list follows:
COUNTRY
NETWORK
DNIC
------------------------------------------------------Australia
Auspac
5052
Australia
Midas
5053
Belgium
Euronet
2062/2063
Canada
Datapac
3020
Canada
Globedat
3025
Canada
Infoswitch
3029
Denmark
Euronet
2383
France
Transpac
2080
France Antilles
Euronet
3400
Germany (West)
Datex P
2624
Germany (West)
Euronet
2623
Great Britain
IPSS
2342
Hong Kong
IDAS
4542
Irish Republic
Euronet
2723
Italy
Euronet
2223
Japan
DDX-P
4401
Japan
Venux-P
4408
Luxembourg
Euronet
2703
Netherlands
Euronet
2043
Norway
Norpak
2422
Singapore
Telepac
5252
South Africa
Saponet
6550
Spain
TIDA
2141
Sweden
Telepak
2405
Switzerland
Datalink
2289
Switzerland
Euronet
2283
USA
Autonet
3126
USA
CompuServe
3132
USA
ITT (UDTS)
3103
USA
RCA (LSDS)
3113
USA
Telenet
3110
USA
Tymnet
3106
USA
Uninet
3125
USA
WUI (DBS)
3104
As you can see, the the United States has many services. But their
DNIC
doesn't follow the pattern I described earlier. (ie. first three digits
represent country, last is service) I am not quite sure why this is, but
I
think it may be because each of the US services listed are privately
owned.
As I was saying earlier, there is a little extra bit of information
you
must give the network when making an international call. Instead of just
emtering the NUA like on a domestic call, you have to enter the DNIC and
append
the NUA or you will not complete you call and probably will get an error
code.
Here is what a call from Telenet to Cambridge University's port selector
in
England, which is located on Euronet (In Britain they call it IPSS.)
would
look like:
TELENET
714A
TERMINAL= d1
@ ID EXAMPLE
PASSWORD?
ID VALID
@ c 234222339399
CONNECTED TO 234 222339399
What I just did was connect to a Telenet port. Enter my NUI. Then
enter
the DNIC for IPSS in Britain (2342) and appended the NUA for Cambridge
University. (22339399) Then I was connected.
REFERENCES
==========
For more detailed info on packet switching and its uses, etc, I
recommend
the following two books:
'Data Communications: Facilities, Networks, and Systems Design'
Doll, Dixon R., New York, Wiley, c1978
'Packet Radio'
Rouleau, Robert and Ian Hodgson, Blue Ridge Summit, Pa., Tab Books,
c1981
ACKNOWLEDGEMENTS
================
Much of the imformation within was provided by:
Cyclone II
Slave Driver
NOTE: This document was written for informational purposes only. Any
application of what was provided within is responsibility of the user,
not the
author.
>>>>>>>>>>>>>>> (c) 1986 TRIBUNAL OF KNOWLEDGE! <<<<<<<<<<<<<<<
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