r10 R 7/82: Explaination of PSNs Name: Doc Holiday #14 Date: 12:34 am Mon Jul 11, 1988 Packet switching networks are designed primarily for on-line applications in which the data must be delivered to its destination immediately. However, there can be a store-and-forward capability which in most cases is used only if a destination terminal is inoperative. A packet of data is usually 128 bytes of data, part of which includes the packet routing control information required to get the packet to its destination. A packet is sent through a communications network as an individual transmission completely independent of the rest of the sentence or block of data. The complete message is normally assembled only at its destination and not at a store-and-forward network computer node. Thus the error detection and correction function is limited to the individual packet of data rather than a block of data. The public packet switching operators have selected an efficient communications protocol similar to CCITT x.25 for transmision of data throughout the network, which includes hundreds of cities around the US and around the world. Unfortunately, most of today's terminals do not operate under the x.25 protocol. To resolve this problem, the network vendors have devised a device called a PAD, which acts as a combionation protocol converter, a packetizer/depacketizer, and a multiplexer. Also available are software protocol converter packages for computers that use the network directly without a PAD. --Continued on next message-- Read:(1-82,7),? : 8/82: PSNs CONT Name: Doc Holiday #14 Date: 12:51 am Mon Jul 11, 1988 The functions of a packet switching network include all of those of a message switching network. Today's public packet switching networks are not looking for the store-and-forward type of operation, although they will provide a mailbox arrangement in which one location sends mail and receives mail as well as the other location. Packet switching networks provide users with a terminal compatibility enhancement feature. Terminals that are not otherwise able to communicate with each other can take advantage of the protocol converter function so, for example, asynchronous terminals can talk to synchronous terminal, and so on.. ADVANTAGES of packet switching networks: The advantages of a packet switching network include those of the mesage switching network. In addition, however, there is the online type of operation that affords the excellent response time that is needed for the brief transmissions between an inquiry or data entry terminal and a host computer. One of the important features of a packet network is the establishment of communications between different types of terminals that ordinarily cannot exchange data without some kind of separate protocol converter. Today's packet switching networks are also noted for their backup lines and alternate routing capability plus a very efficient, cost-effective use of the network. "I feel like I'm rambling.. so I'll stop." --Phantom Phreaker --Doc Holiday Read:(1-82,8),? : 9: Text Philez P-Z [UD:Punter][Unltd.Time][UnltdBlk]: