t TV without FEC) without FEC) 8.448Mbit/s 10-7 with FEC(10-8 10 5 with FEC(10-9 34.368Mbit/ without FEC) without FEC) 41/20 Asynchronous Transfer Mode cells and this is regarded as the minimum adaptation layer function- acknowledgment. (Called user response time is not included.) ality for all services. Cell header errors affecting the destination Provisional target maxima based on the I.352 figures for 64 address field could lead to lost cells with potential violation of kBit/s ISDN are: service privacy and security, therefore such errored cells are dis- Mean connection set-up delay of 4500ms. carded. Discard, however, can also have a deleterious effect on 95% connection set-up delay of 8350ms. some services, particularly video where some coding algorithms 2. Connection release delay, which is the interval between the may give error extension to a complete video frame. In this context, event of the call release message transfer and receipt of its CLRs of 10-11 might be required and this is a very demanding target acknowledgment. Provisional target maxima based on the 1.352 in terms of buffer lengths in the ATM network. Signals of higher figures for 64kbit/s ISDN are: digital hierarchies, 8 Mbit/s and 34 Mbit/s, may lose synchronisa- Mean connection release delay of 300ms tion if a cell loss affects justification control bits. Thus for all the 95% connection release delay of 850ms. high bit-rate services a FEC in the terminals for bit errors and cell losses may be necessary. 41.6 References 41.5.1.3 Cell Insertion Ratio (CIR) Anagnostou, M.E., et. al. (1991) Quality of service requirements in ATM based B-ISDNs, Computer Communications, May. This is the ratio of inserted cells to total number of cells entering a Andersen, I., Sallberg, K., Stavenow, B. (1990) A resource alloca- VC. It results from header bit errors in the address field. Cell tion framework in B-ISDN. In Proceedings of the X111 Interna- insertion is considered more serious than cell loss: for some services tional Switching Symposium (ISS '90), 1, 