 of CE and ATM boards ERICSSON ATM boards: 4 X STM-1 (4 X 155 Mbps) 1 X STM-4 (622 Mbps) 8 X E3 (8 X 34 Mbps) 26 X E1 (26 X 2 Mbps) CE boards: 16 X E1 (16 X 2 Mbps) 1 X STM-1 (155 Mbps) 2 X STM-1 (2 X 155 Mbps) Figure A4.6 Possible interface boards in an MSG backbone network consists of ATM core switches that support some basic requirements, such as setting up switched virtual circuits (SVCs) using the standardized signalling UNI 4.0 and PNNI 1.0. To calculate the required number of MSGs in a certain network solution the number of interface boards of different kinds must be examined. TDM Interfaces and Circuit Emulation in an MSG Let us start to calculate how many circuit emulation boards we need. We can use either interface boards with 16 E1 capacity, or we can use STM-1 interfaces with two assumed variants, either one or two STM-1 interfaces per board. In our example we will use the two alternatives 16 E1s or 1 STM-1 per board. As input data we need to know the number of subscribers and the average traffic per subscriber, or as an alternative the number of E1s, if this information is avail- able. For simplicity reasons we assume that the utilization of the E1s is 80 %. See Figure A4.7. CE for voice, access side N = No. of subscribers at = total traffic per subs. (orig. + term.) A = N X at = total access traffic u = utilization per speech channel Channels to CE = A/u = Nx at/u E1s to CE = N X at/u/31 E1s/16 = > number of E1 CE boards Voice STM-1s to CE = E1s/63 No. of subscribers CE boards 16 X E1 per board, 14 boards per sub-rack 1 X STM-1 per board, 14 boards per sub-rack Figure A4.7 Calculation of the number of CE boards needed Appendix 4: Dimensioning Media Gateways and Associated Telephony Servers If we do not know the number of E1s on the access side, we can easily calculate this by dividing the total access traffic with the utilization factor (80 %) and with the number of channels per E1 (31). Dividing this result by 16 gives us the number of circuit emulation boards. As an STM-1 trunk can carry 63 multip