Appendix A: Selected Backhaul Scenarios in MPLS-Based Access Networks
In this Appendix, we look in detail at how traffic can be back-hauled across an MPLS-based access network. The scenarios we look at are for the case where the access networks and core networks are separate MPLS islands, with a non-MPLS hand-off between access and core. First, we will examine the case of dedicated business VPN services and then we will examine some DSL scenarios. This Appendix assumes familiarity with the connectivity blueprints shown in Figure 16.2 of Chapter 16.
A.2 DATA SERVICES FOR BUSINESS CUSTOMERS
Let us assume that the service provider is offering the following services to business customers:
- L3VPN. As discussed in the L3VPN chapter, at the time of writing this was the predominant MPLS-based service offered to business customers.
- L2VPN service, as a replacement for leased lines and ATM and Frame Relay services.
- VPLS service for LAN interconnect.
- Internet access service. In the case of some service providers, Internet routes are stored in the main routing instance of the service node (SN). In other cases, an L3VPN is used as the internal infrastructure for Internet service, with the routes being stored in a particular ‘Internet VRF’. Either way, the traffic needs to be carried across the access network between the customer sites and the SNs.
Note that in some cases, the Ethernet access network also carries PSTN bearer and signaling traffic. Often an L3VPN is used as ...