Assumptions :
»the speech channels carry a traffic load of 0.75 Erl
»the average call duration is 100 seconds
»the signaling link is used at a rate of 0.2 Erl
»each call setup and call release involves the transmission of 14 information blocks with 12 bytes each ( per POTS subscriber ) and 24 bytes ( per ISDN subscriber )
Explanation :
»per hour every speech channel carries 3600/100 * 0.75 = 27 calls
»per hour every speech channel 27*14*24 = 9072 bytes of info must be transmitted ( 4536 bytes from exchange A to B and 4536 bytes from exchange B to A )
»a circuit transmits 64000 bits/sec or 8000 bytes/sec or 8000*3600*0.2 bytes/hour I.e 5760000 bytes/hour
»with each voice channel transmits 4536 bytes a signaling circuit can support 5760000/4536 = 1269.84 voice circuits.
