User-Network Interface-Layer 3 Specification for Basic Call Control. Rosen, E., Viswanathan, A., and Callon, R. (2001) RFC 3031, IETF. Rastislav, S. (2001) Technical Overview of IPSS and BBCS, Proceedings Swisscom SwiNOG 3. Simpson, W. (1994) The Point-to-Point Protocol (PPP), IETF, RFC1661 STD 51. This page intentionally left blank 13 Multiprotocol Label Switching Martin Reed University of Essex Introduction Multiprotocol Label Switching (MPLS) is a methodology of controlling switched networks that has been designed to be compatible with IP networks. This is unlike many other switched-network solutions that have been developed separately from IP and that inter- operate with variable degrees of success. This chapter starts by introducing the MPLS architecture, which includes the components and the methodology of switching to create a Label Switch Path (LSP). The architecture is supported by signaling that sets up the LSP. The signaling is fairly complex because there are a number of LSP signaling protocols; therefore, only an overview of the main protocols is presented and the motivation for their existence is given. The final parts of this chapter describe the two main applications for MPLS: traffic engineering (including quality of service) and providing carrier-grade Virtual Private Networks (VPNs). These two applications are considered separately, although of course it is possible (and likely) that they will be used together. Before considering the MPLS architecture in detail, the basic principle and history behind its evolution are described. When considering MPLS in detail it becomes clear that it is a complex architecture and set of protocols. The reason for this is partly that, rather than being created as a new protocol, MPLS has evolved from a set of competing technologies. Another reason for the complexity is that MPLS has been designed to be truly "multiprotocol" in that it can, in theory, support many higher network layer protocols over a variety of link layer protocols. In this chapter the only netw