o as 34Mbit/s than the kHz required for the early multi channel telephony systems. and 140Mbit/s respectively. For the original UK black and white television broadcast standard Straightforward PCM coding of 625 line PAL generates a digital of 405 line, 2:1 interlace, 50 fields (25 frames) per second, the video signal with a bit rate of about 100Mbit/s. The CCIR component bandwidth was of the order of zero to 3MHz in all sections of the digital standard (Rec. 601, 4:2:2) for YUV components generates a programme chain from camera to transmitter, and similarly for the source signal of 216Mbit/s. Recently developed video bit rate re- video amplifier in the receiver. This stimulated the development of duction techniques can reduce the bit rate by a factor of about 8 to broadband, linear circuitry and transmission systems which soon 10 times; feasibility studies, using computer simulation, suggest found application also for multiplexed telephony transmission. that it may be possible to reduce video bit rates by a factor between Within the television broadcasting environment, communication about 20 and 40, permitting digital broadcasting to the home of 625 links include the routeing systems within the studio complex, link- line composite or component video within the bandwidth of terre- ing cameras with mixers (switchers) and between mixers and a strial TV channels. An example of such studies is the Eureka 625 central apparatus room etc., often involving hundreds of metres of project VADIS (Video Audio Digital Interactive System) aimed at cabling; contribution links from OB (remote) venues to the studio multiplexing video, audio and data information for transmission in centre or for incoming 'live' programmes from distant studio high speed LANs and future broadband telecommunications net- centres or overseas broadcasters; distribution links from studio works. centres to transmitters, including the inter city links required for Video bit rate reduction involves the use of such techniques as network operation, inter count