est office in an organisation at a competitive price. This should even extend to the desk of the 56.3.2 Compression user, giving full management control to the network management system. Features within the multiplexer will also include: Compression techniques both for voice and data offer advantages in optimising the digital service. Data compression can offer effective- 1. Multidrop capability to mirror analogue IBM multidrop envi- ness of 8 to 1 using such techniques as statistical multiplexing. ronments. Voice compression development however, has been more pro- Integration into umbrella management systems such as IBM nounced and on international circuits can realise enormous cost Netview, AT&T UNMA, DEC Enterprise Management Archi- saving. tecture, CCITT Telephone Management Network, and of The compression technique adopted by the original multiplexer course OSI management environment. vendors was proprietary, called CVSD (Continuous Variable-Slope 3. The ability to migrate to ISDN technology. Delta Modulation). 4. Support of such capabilities as PCM bridging, and conference This offers compression successfully down to 24kbit/s (nearly 3 and virtual channel capability. to 1 over PCM) but is plagued by bad quality and high delays. A technique which became standard within CCITT G.721, called The development of digital Wide Area Networking based on the ADPCM (Adaptive Differential Pulse Code Modulation) was there- multiplexer platform is a reality of corporate private service. Its role fore integrated on to the earlier multiplexers and became a standard is now either being enhanced or under threat, depending on the point for all new generations. This offered 32kbit/s (2 to 1 compression), of view, due to the sudden growth of Local Area Networks. was of acceptable quality and minimal delay. Its quality also allowed fax to be sent across 32kbit/s unlike CVSD. Most recently new techniques have been adapted, the most promi- nent being Code Excited Linear Prediction (CELP). This offers 56.4 Development of Local Area 