eotelephony/conferencing; for a number of important and characteristic services. Some of the structured (CCITT Rec. issues governing choice of parameter values are discussed and the 1.231.8) values proposed for each bearer service are given in tabular form. (Tables 41.5 and 41.6.) This material is based on a literature survey 1.92Mbit/s unrestricted, 8kHz Videoconferencing; data and analysis made at the National Technical University of Athens as structured part of the RACE project 1014 'Atmospheric' (Anagnostou, 1991). 2.048Mbit/s Circuit emulation (multiplex The network oriented QoS sub-attributes are sub-divided into two signal) categories: information transfer related and call control related. > 2Mbit/s up to < 130Mbit/s Data; image; video Approx. 1Mbit/s Stereo sound contribution 41.5.1 Information transfer parameters unidirectional 45-130Mbit/s unidirectional TV contribution These are as in the following sections. 8.448Mbit/s Circuit emulation 41.5.1.1 Bit Error Ratio 41.5.1.2 Cell Loss Ratio (CLR) This is the ratio of the number of bits incorrectly received to the total This is the ratio of lost cells in a given VC to the total number of number of bits sent. In ATM it may be applied to the Cell informa- cells entering the VC. Cell loss may occur due to errors in the header tion field only. It is expected to be no higher than the BER in present of the cell (misrouted cells) or due to buffer overflow. CLR is a key STM networks and will probably improve further with the introduc- performance parameters in an ATM network and is an ATM specific tion of optical transmission systems. attribute. Cell loss can be detected using sequence numbering of Table 41.6 Provisional QoS parameter values for bearer services Bearer service End-to-end Cell delay delay variation 64kbit/s 400ms 2 X 64kbit/s 200ms Connectionless access interoffice signalling 384kbit/s - 1.92Mbit/s 200ms > 2Mbit/s 10-7 with FEC(10-8 10-5 with FEC (10-9 200ms without FEC) without FEC) Stereo sound 10-7 with FEC (10-8 10-5 with FEC (10-9 500ms Broadcas