 Protocol used to interconnect more than one autonomous system. It is used by Internet core routers and is designed to prevent routing loops in arbitrary topologies and to allow policy based route selection. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. Reachability information includes a list of autonomous systems (AS) traversed. The BGP supports any policy that confirms a 'hop-by-hop' routing paradigm. The latest version, BGP4, is designed to handle scaling problems of a growing Internet. BGP4 provides a new set of mechanisms for supporting classless interdomain routing. The BGP uses the TCP as its transport protocol. It uses TCP port 179 for establishing connections. The TCP meets the BGP's transport requirements and Core Network Planning and Optimisation BSSGP Network Network Service Service Figure 4.46 GPRS Packet Core Protocol stack is present in almost all commercial routers and hosts. Since the BGP is running on the TCP, which is a reliable transport protocol, there is no need for the BGP to handle fragmentation, retransmission, acknowledgement and sequencing. Any authentication scheme used by the transport protocol can be used in addition to the BGP's own authentication mechanism. Any two systems that follow BGP exchange complete BGP routing tables initially. Consequently they exchange only incremental changes. Keep alive messages and error notifications are also exchanged between two BGP hosts. 4.11 Dimensioning Dimensioning involves defining recommendations for a proposed backbone network, calculation of intersite and intrasite traffic figures for planning, calculation of the transmission capacity required across multiple core network sites and defining the appropriate number, capacity and type of recommended core equipment. Dimensioning is useful in presales support and consultancy type of work requiring a ready definition of alternative network solutions/scenarios. It helps in core network architecture design development and conc