A hashing scheme for phone number portability in PCS systems with ATM backbones

Abstract

Current cellular subscribers have a geographic phone number (e.g. in AMPS and US digital cellular systems) or a number which contains the network provider's identity (e.g. in GSM), and whenever subscribers register or receive (and possibly, originate) a call, a home location register (HLR) database has to be queried. A special feature of next generation wireless access service will be to support PCS and wireless subscribers with portable personal numbers, or non-geographic phone numbers (NGPN), that do not indicate the service provider or HLR database serving the user. In addition the global title translation (GTT) function that converts the subscriber's number to an HLR database address may not be available when the wired backbone is an ATM network. Thus a key function required will be to translate an NGPN to the ID of the HLR which serves the subscriber, a process we call NGPN translation. (Note that the same functionality is also needed for subscribers with local, portable phone numbers.) We discuss the requirements of NGPN translation and some alternative schemes. We propose a scheme for fast, efficient, scalable and flexible NGPN translation which applies ideas of dynamic hashing, caching, and indirection. The scheme uses a hash function in the visiting location registers (VLR) (or serving SCP) and a set of distributed translation servers which store the NGPN-to-HLR mapping.