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  1. N. Beijar, Telephony Routing with Support for Number Portability in Interconnected Circuit and Packet Switched Networks, Licentiate thesis, Helsinki University of Technology, 2004 (pdf)(bib)
    Abstract: Telephone networks are currently facing two major changes that affect routing. Firstly, number portability is gaining popularity. Number portability requires a mapping between the number dialed by the subscriber and the number used for routing. Secondly, Internet Protocol (IP) telephony is gradually replacing circuit switched telephony. As both technologies must co-exist for several years, a need arises to provide seamless routing between the technologies. This involves the process of locationing the best gateway for each call between the technologies. This licentiate thesis examines the problems of routing, gateway location and number portability in interconnected circuit and packet switched network. The problems and their current solutions are first described and evaluated. We observe that the current solutions address each of these subproblems separately and only in a single technology, while an efficient solution requires that all problems are observed simultaneously. We therefore establish a set of requirements for information distribution and usage of routing addresses. We then propose extensions to existing methods to enable better performance and integration with other methods in a hybrid scenario. Specifically, we examine solutions based on the Domain Name System (DNS), the Telephone Routing over IP (TRIP) protocol, and databases. Because it is doubtful that a single method would be used in all networks and in both technologies, we examine combinations of methods. Further, we find that scalability can be improved by using two specialized consecutive mappings. We group the methods into schemes according to the involved types of identifiers and select a few feasible schemes. The schemes and the application of specific methods on the schemes are evaluated. Finally, different properties of the methods are analyzed and especially scalability is considered.