Mobile Switching Center: It co-ordinates the activities of the entire base stations and connect the entire cellular system to the PSTN. A typical MSC handles 100,000 cellular subscribers and 5,000 simultaneous conversations at a time, and accommodates all billing and system maintenance functions as well.

Home Location Register: Permanent database about mobile subscribers in a large service area.Database contains subscriber & location information. Database contains prepaid/postpaid, roaming restrictions, supplementary services.