sion. Optical sources. Optical detectors. for ATM. Quality of service performance requirements. References. Optical receivers and transmitters. Optical system design. Applica- tions of fibre optic communications. The future of fibre networks. 42 The Synchronous Digital Hierarchy (SDH) Introduction. PDH deficiencies. The basis of SDH. The SDH stand- 54 Packet switching ards. Control and management. SDH based networks. Impact of History and underlying concepts. Packet switched call. The packet broadband standards. Future technologies. Conclusions. Refer- switched network. Packet switching and the OSI model. Datagram ences. networks. Routeing over packet switched networks. Packet switch- ing equipment. 43 Signalling systems Analogue network signalling. Common channel signalling. Digital network signalling. References. 55 Fast packet switching Introduction. Frame Relay. Cell Relay. Conclusions. References. 44 The Integrated Services Digital Network Introduction. International standards for ISDN. ISDN services as- 56 Local and Wide Area Networking pects. Network aspects. User/network interfaces. ISDN develop- Introduction. Network development. Digital networks. Develop- ment in the U.K. ISDN applications. Broadband ISDN. ment of Local Area Networks (LANs). Interworking devices. Bibliography. LAN/WAN challenge for the 1990s. Acknowledgement. Contents 57 Video transmission 60 Facsimile transmission Principles of video transmission. Television transmission. Cable Introduction. Facsimile types. CCITT document facsimile equip- distribution systems. Digital video coding. Videophony and video- ment. G3 facsimile equipment. 64kbit/s facsimile equipment. G3 conferencing. References. networks, switches, gateways and PCX fax. Facsimile futures. Bib- liography. 58 Telephones and headsets 61 Telecommunication system Telephones. Telephone speech functions. Telephone transmitters. measurements Telephone receivers. Telephone handset design. Telephone trans- Digital circuit testing. Interface measurements. Error performance mission pe