depending upon the implementation whether it is gsm based(map) or cdma(ansi) based.
u have to start with analysis.say for a location update u have 4 message which gets transferred between the msc and the hlr . now depending upon the size of the message say it is 40kb .now u need to calculate the nos of subscriber u expect.. followed by the anaysis as to whether it is e1/t1 media(64kbs or 56kbs) u calculate the nos of message tht can be transfered over the link..now u have to calculate for nos of links between the nodes depending upon ur data …