(2)同步传输 1)概念 With synchronous transmission a block of bits is transmitted in a steady stream without start and stop codes. The block may be many bits in length. To prevent timing drift between transmitter and receiver, their clocks must somehow(某种方 式) be synchronized One possibility is to provide a separate clock line between transmitter and receiver. One side(transmitter or receiver) pulses the line regularly with one short pulse per bit time The other side uses these regular pulses as a clock. Th technique works well over short distances as the data signal but over long distances the clock pulses are subject to the same impairment (afi) as the data signal, and timing errors can occur 网络通信网络通信 8 （2）同步传输 1）概念 With synchronous transmission, a block of bits is transmitted in a steady stream without start and stop codes. The block may be many bits in length. To prevent timing drift between transmitter and receiver, their clocks must somehow（某种方 式）be synchronized. One possibility is to provide a separate clock line between transmitter and receiver. One side (transmitter or receiver) pulses the line regularly with one short pulse per bit time. The other side uses these regular pulses as a clock. This technique works well over short distances as the data signal, but over long distances the clock pulses are subject to the same impairment （损伤）as the data signal, and timing errors can occur