18.10.1 Professional Systems

Professional systems are characterised by high performance and equipment ruggedness. They tend to be the point-to-point applications identified in Section 18.9.2 above. The implementation for professional applications has been governed by particular standards developed by CCITT/ITU-T18,19. However, in the case of the video and audio compression processes, advantage has also been taken of standards developments such as MPEG which have enabled the production of VLSI devices for the very large markets anticipated for a wide range of video services. Whereas some suppliers of professional compression systems have taken a nonstandard approach, there is now a clear preference in the market place for MPEG-based schemes since they provide a more secure means of ensuring that, as technology develops further, there will be no short-term obsolescence and a clear upgrade path.

Early commercial product from some suppliers adhered closely to the MPEG specifications, first MPEG-1 and later implemented MPEG-2 video processing, including full resolution, B frames and field/frame processing. Full MPEG-2, complete with the systems layer multiplex, has been available in product since 1994. The devices to perform the video decompression are available from several sources, some public and some tied to particular projects such as DirecTv (see above). There are also VLSI devices which can realise the Viterbi decoding of the convolutional forward-error-correction scheme and which allow digital demodulation of QPSK. The realisation of the MPEG-2 systems layer multiplexing functions took some time to appear in VLSI since the specifications were only finalised at a meeting...