ice Max. capacity for voice ao = 0.05 erl. u = 80% pV = 20% CP-calls per sec. (cps) sV = 120% 0.05 X (2-0.2)/120 < 50 Voice: N ao(2-pV)/pV max. 50 cps/sub-rack Nmax = 67 k E1 max = 270 (>224) max. 4 STM 1 CE in a sub-rack Figure A4.15 Calculation of the processor capacity in an MSG Understanding Changing Telecommunications - Building a Successful Telecom Business CH-Capacity-MSG CH capacity Calculation model ISUP ref. calls/s Work load factor (WL factor) Intra-domain call Inter-domain call RSS (POTS) 1.0 ISUP: (E1s) PRA/DSS1 DSS1 (PRA) V 5.2 ISDN Dial-UP ISP not avail. CHC: 50/(WL FACTOR ) calls/s Portion PBX/PRA calls/s % Workload (WL) Figure A4.16 Example of work load factors This is illustrated in Figure A4.16. A simple way to handle these differences is to define a reference type of call (ISUP inter-MGW intra-domain) and allocate different workload factors for the other types of call, in relation to the reference call type. In Figure A4.16 the work load factors for intra-MGW calls have not been included. Different Access Types and Load Factors The processor load, caused by the MGW application, on the call handler in the MSG, will depend on the amount and type of accesses (i.e. ISUP/PRA/V5.2 etc.) being connected. The assumed amount of traffic for each one of these access types will have impact on the CP load. For example, the ratio between the number of messages needed for the set-up and call release phase for a PRA/DSS1 access compared to an ISUP access is approximately 1.6. Processor Capacity To make sure that one sub-rack is enough in the case with STM-1 interface, we must also check the processor capacity. See Figure A4.17. Note. A MSG can have more than one CP pair. Voice Regarding voice the processor in the MSG has to handle all the originating calls plus all the incoming calls. The number of calls per second (cps) can be calculated with the formula A = y X S. So, dividing the traffic figures by the mean holding time (s) gives us the number of calls per second. The result of the calculation example in F