hannels Direction of data flow 48 + 5 octet cells Video data LAN data Voice traffic Figure 40.17 Use of fixed length cells for the transport of data (Compare with Figure 40.16) cells) of 48 octets for the information field and 5 for the header. 40.10 References Because these cells are SO simple in structure, they can be im- plemented in hardware rather than software (as for X.25 packets). This means gigabit speeds will be achievable. Brewster, R.L. (1987) Telecommunications Technology, Ellis Hor- Different data services such as computer data, video and voice, wood Ltd. break up their data streams into the cells for transmission over the CCITT (1988) Data Communications over the Telephone Network, network where they are recovered at the remote end. As with frame Series V Recommendations, Vol. VIII, Fascicle VIII.I. relay, errors are not detected and recovered by the network but by the transport layers in the end systems (OSI layer 4) which initiate CCITT (1988) General Aspects of Digital Transmission Systems, the data recovery mechanisms on a peer to peer basis across the Recommendations G.700-G.795, Vol. III, Fascicle VIII.4. network. Obviously such a technique relies on a very efficient high CCITT (1990) Draft proposals on B-ISDN, Recommendations speed, low error transmission path for efficient throughput. This can 1.113, 1.150, 1.311, May. be provided by fibre optic cables running at the speeds quoted above. Davis, D. and Barbar, D. (1973) Communication Networks for Computers, John Wiley and Sons. Figure 40.17 shows how fixed length cells, each carrying different types of data, are multiplexed down a link. The VPI/VCI is only Halsall, F. (1988) Data Communications, Computer Networks and assigned on a cell by cell basis. It is the address in the cell header OSI, Addison Wesley Publishing Co. that determines the route taken. This makes for a highly efficient use Ronayne, J. (1991) Introduction to Digital Communications Switch- of bandwidth using the best of TDM and statistical multiplexing. ing, Pitman Publishing