MPLS-Enabled Applications: Emerging Developments and New Technologies

11.11. OTHER APPLICATIONS OF LAYER 2 TRANSPORT

In this chapter so far, we have discussed how the Layer 2 transport mechanisms can be used to supply explicit Layer 2 services to enterprise customers. These Layer 2 transport mechanisms are also used as internal infrastructure tools in service provider networks and as a means for service providers to offer specialist services to other service providers. Some examples are listed below:

• Layer 2 connections can be used to provide access circuits to other services. For example, if a service provider is offering a Layer 3 VPN service to a customer, rather than providing a traditional leased line connection from the CE to the Layer 3 VPN PE, they may use an Ethernet-based pseudowire between the CE and the Layer 3 VPN PE across an MPLS-enabled metro Ethernet infrastructure. This is discussed in more detail in Chapter 14 of this book.

• Smaller service providers sometimes have fragmented networks, each based in a particular region or city. They can use Layer 2 transport services bought from larger service providers to provide interconnections between these isolated islands.

Some service providers also offer smaller service providers a connection to a public peering exchange by means of an Ethernet pseudowire. In this way, the customer of the service does not need to have a router at the peering exchange yet can still enter into peering agreements with other companies present at the peering exchange. This is illustrated in Figure 11.6. Service ...