I. Introduction
Traditional telecommunication networks were designed to carry fixed telephone, data, mobile telephone and internet services separately. Transport and service networks were supplied by a single vendor and interoperability was limited to interconnection gateways. The emergence of IP has resulted in the evolution of these networks to NGN. The International Telecommunication Union Telecommunications Standardization Sector (ITU-T) has defined the NGN as a packet-based All-IP network capable of making use of multiple broadband, QoS-enabled transport network technologies [1].