n. If LDP is the protocol for tunnels management, tunnels routing is performed by Border Gateway Protocol (BGP) [37]. As we have seen, every LSR decides in an autono- mous way (it is said an autonomous system) what is the suitable output port to route a new tunnel. The primary function of a BGP is to exchange information about the presence of net- work connections linking a BGP system with other BGP systems. This network connec- tivity information includes information on the list of autonomous systems that the BGP packet traverses. This is sufficient to build inside each LSR a local graph of the network that is the base to perform the routing loops needed to construct the routing table of the LSR. Due to its fundamental function for the network optimization, the BGP was updated several times SO that several versions exist. The current version, BGP4, among other improvements, introduces mechanisms that allow aggregation of routes in subnetworks and aggregation of tunnels in tunnel classes. These features are important for the evolu- tion of MPLS toward a generalized network control plane that will be discussed in detail in Chapter 8. Telecommunication Networks In order to increase the efficiency in network resources exploitation and to faster net- work survivability, the MPLS standard defines both centralized traffic engineering and fast reroute tunnels (FRR tunnels). The first feature assumes that an off-line global traffic engineering tool is available to the carrier. If it is true, routing the network tunnels via this tool will require an off-line operation, much slower with respect to standard network working, but it will also give a more efficient network resources allocation. Thus, the MPLS also implements a fea- ture allowing the central network management to route manually a few paths follow- ing the indications of the off-line traffic engineering tool in order to improve network efficiency [37]. In order to implement fast survivability, MPLS needs to route a couple of FRR tunnels [38,39]. They are tunnels