12
Layer 2 Transport over MPLS
12.1 INTRODUCTION
This chapter describes the rapidly growing area of Layer 2 transport over MPLS networks. This is a key component of a multiservice network as it allows service providers to migrate Frame Relay, ATM and leased-line customers to an MPLS network while maintaining similar service characteristics from the customer's point of view. It also enables new Layer 2 service offerings based on Ethernet access. In this chapter, we compare the two main schemes for achieving Layer 2 transport over MPLS, one based on LDP signaling and the other based on BGP signaling. We also discuss Circuit Cross Connect (CCC), which was the precursor to these schemes and is still in use in several service providers’ networks.
12.2 THE BUSINESS DRIVERS
Native Layer 2 services have existed for several years, based on Frame Relay or ATM. Often these services are used by an enterprise to build its corporate Layer 2 VPN by interconnecting its LANs over a wide area. Service providers can offer near global reach, either directly or through interconnection agreements with partners. The services are a valuable source of revenue to service providers, at the time of writing far outstripping revenues from IP services. In these networks, customer sites are interconnected at Layer 2, sometimes in a full mesh but more typically in a hub-and-spoke topology. The role of the service provider is to transport the ATM cells or Frame Relay frames over the wide area, at an agreed bit-rate ...
