h more accurate data flow. Remember that what is beneficial or not beneficial about a particular network depends on the prevailing conditions, so in an analog infrastructure where noise was an issue, error control was a highly desirable feature. But performing that error control procedure on every packet, at every node, in addition to looking up the proper routing instructions at each intermediate node for the next point to which to relay the packet, increased the delays encountered end to end during transmis- sion. Because X.25 packet-switching networks were for data only, it was not impor- tant to be able to tightly control delays or losses; the endpoints would resolve any such problems. Chapter 7 Wide Area Networking While X.25 networks are still found around the world, their use is in dramatic decline, and they are being replaced by newer technologies, including Frame Relay, ATM, and the much-favored IP. However, in many portions of the developing world, X.25 is still often the only available reliable service and is used mainly in legacy trans- action systems. Another common application has been automated teller machines (ATMs), but as more and more of these banking kiosks today involve multimedia interfaces, many of them are moving to higher-speed connections. Packet Size in X.25, Frame Relay, and ATM An early attribute of X.25 was the size of its packet. It used relatively small packets, gener- ally 128 bytes or 256 bytes long. Small packets were desirable in the X.25 generation because of the noise factor. If there was noise in the network, there would be errors, and hence fairly frequent retransmissions were necessary. Retransmitting a smaller packet is more efficient than retransmitting very long blocks of information, so X.25 was specifi- cally designed to use small packets. In the next generation of packet-switched networks, Frame Relay, the packet sizes are variable, but they can be up to 4,096 bytes. Frame Relay operates over a digital net- work, where noise is not much of an issue because regenerati