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[] []
[] THE INS AND OUTS []
[] OF []
[] PACKET SWITCHING []
[] []
[] by: The Seker []
[] 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.
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