TAILIEUCHUNG - Lecture 26: Switching
Message switching: In message switching no physical path is established in advance between sender and receiver. Instead, it is sent and stored in the first switching office (., router) and then forwarded later, one hop at a time. Each block is received in its entirety, inspected for errors, and then retransmitted. Telegrams were message switching. This technique needs routers with big buffers and also a single block may tie up a router- router line for minutes, useless for interactive traffic. Packet switching gets round this problem. . | CSN200 Introduction to Telecommunications, Winter 2000 Lecture_26 Switching Switching: (Ref: Ch-9 of your Text book) Three different switching techniques are used inside the telephone system: 1. Circuit switching 2. Message switching (using store-and-forward network). . Packet switching 3. Virtual circuit switching - a compromise between circuit switching and packet switching. The actual service offered is connection oriented, but it is implemented internally with packet switching. Circuit switching: In circuit switching, a physical connection established by the switching mechanism. Once a call has been set up, a dedicated path between both ends exists and will continue to exist until the call is finished. Fig 2-34, 2-35 Tanenbaum An important property of circuit switching is the need to set up an end-to-end path before any data can be sent. As a result of the established path, there is no danger of congestion, but wastes bandwidth. Message switching: In message switching no physical path is established in advance between sender and receiver. Instead, it is sent and stored in the first switching office (., router) and then forwarded later, one hop at a time. Each block is received in its entirety, inspected for errors, and then retransmitted. Telegrams were message switching. This technique needs routers with big buffers and also a single block may tie up a router- router line for minutes, useless for interactive traffic. Packet switching gets round this problem. Packet switching: In Packet switching no physical path is established in advance between sender and receiver. Instead, it is sent to the first switching office (., router) and then forwarded to the next, one hop at a time. Each block is received in its entirety, inspected for errors, and then retransmitted. The only difference from the message switching is that, the block size is small, so no need to store, packets can be buffered in router's main memory instead of on disk. This limit on the .
đang nạp các trang xem trước
