[][][][][][][][][][][][][][][][][][][] [] [] [] THE INS AND OUTS [] [] OF [] [] PACKET SWITCHING [] [] [] [] by: The Seker [] [] Tribunal of Knowledge! [] [][][][][][][][][][][][][][][][][][][] [] Written (c) June 23, 1986 [] [][][][][][][][][][][][][][][][][][][] 'TRIBUNAL COMMUNICATIONS LTD' """""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""" 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 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! <<<<<<<<<<<<<<<