an Area Networks-Virtual Bridged Local Area Networks-Amendment: Provider Backbone Bridge Traffic Engineering, IEEE, June. 36. ISO/IEC 10589 (2002) Information technology - Telecommunications and information exchange between systems - Intermediate System to Intermediate System intra-domain routing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode network service (ISO 8473), ISO/IEC. 37. Metro Ethernet Forum (2008) Carrier Ethernet Services Overview, September. 38. RFC 3031 (2001) Multiprotocol Label Switching Architecture, IETF, January. 39. TeliaSonera International Carrier (2006) Why it pays to buy IP Transit instead of building your own international IP network, June. Core Networks and Operations Support Systems 8.1 Introduction Core Network (CN) and Operations Support Systems (OSS) are the two network components that are discussed in this chapter. The details of 3GPP Core Network evolution from Release 99 to Release 8 are provided which show a transition from circuit switched to packet switched and reduction in the number of core network elements. This migration from a mix of circuit switched and packet switched (Rel-99) to all IP packet switched core (Rel-8) is of keen interest not only to the industry but also to academia. The core networks of 3GPP2, MBWA, and WiMAX systems are also briefly discussed. In the following section some key enhancements in the core network for example Next Generation HLR and Generic Authentication Architecture will be highlighted. The CN study will be followed by the OSS details and analysis. Still today, OSS is not receiving as much attention as compared to the rest of the elements of the network. The operators are still more focused on the evolution of radio, transport and core networks than OSS. The ITU-T started an ac- tive role in the 1990s and provided principles of Telecommunications Management Network. Later on Telecommunication Management Forum was established in 1988 to streamline the different ITU-T and third pa