Packet Switching Types: ATM, Frame Relay, TCP/IP, X.25

Transmission: SONET T-Carrier

Services: [3G] [4G] [Bluetooth] [I-Mode] [WAP] [Wireless and packet switching]

X.25 Networks

One of the earliest packet switching schemes, X.25 was was the first non-telex data network the Bell System deployed. Designed to work with metallic analog telephone lines and electromechanical switches, X.25 has an error correction overhead that severely limits its speed. Still, it is an extremely accurate way to pass data and is still used by many companies, especially where accuracy counts, not necessarily speed, such as for credit card verification. It is quite a different protocol than TCP/IP. For a good introduction to X.25, read this selection by Regis Bates:

A nice introduction to X.25 by Bates (180K, seven pages in .pdf) from The Broadband Telecommunications Handbook by Regis J. Bates

The F.C.C. definition of packet switching and X.25

"Packet-switched technology segments data into relatively small blocks before transmission. Each block, known as a packet, contains user data and control information. The control information typically includes flags marking the beginning and end of the packet, source and destination addresses, sequence number, and error detection/correction codes. Packets are routed through the network one at a time, and may arrive at their destination by different paths and out of sequence. The computer at the receiving node is responsible for reassembling the packets into the correct sequence before passing them on to the user. A certain amount of transmission delay is inherent in packet-switched networks, but they make efficient use of network resources for bursty data traffic that is not highly time-sensitive."

"Commercial packet-switched networks operate according to the well-established X.25 international standard. The standard was developed during the 1970's for use over electrically noisy analog copper transmission facilities that tended to introduce errors. Every switching node in an X.25 network goes through a rigorous, time-consuming procedure to check the validity of the structure and routing of a packet before passing it to the next node where the process is repeated. The technique has been widely and successfully implemented, but it is limited to a speed of 64 kbps, and it is not suitable for the transmission of voice or video information."

An Ericsson comment

From their most excellent telephony primer now located here:

http://www.ericsson.com/support/telecom/index.shtml

"An advantage of X.25 - as compared with data communication in circuit-switched networks - is that data can be sent to more than one receiver at the same time. Packet switching also enables communication between terminals that have different transfer rates and different types of interface."

"The global availability of public X.25 networks is another factor that favours X.25 communication. Built-in functions for error detection and correction ensure safe transfer even on circuits of rather low quality. This makes X.25 ideally suited for long-distance, bursty data communication over links of limited transmission quality."

"The protocol's applicability is limited by the bandwidth. Traditionally, the maximum bandwidth of X.25 has been 64 kbit/s, but some of today's X.25 networks use a bandwidth of 2 Mbit/s. Even that capacity is often insufficient for the interconnection of private networks (LAN interconnect). Frame relay and ATM are more powerful alternatives for such interconnection."

Packet Switching Types: ATM, Frame Relay, TCP/IP, X.25

Transmission: SONET T-Carrier

Services: [3G] [4G] [Bluetooth] [I-Mode] [WAP] [Wireless and packet switching]