EnterpriseService Provider Relationship and Interface

Enterprise/Service Provider Relationship and Interface

In today's typical private-line, ATM, and Frame Relay networks, the responsibility for specific portions of the network is very clear-cut. The enterprise is responsible for the end-to-end network at Layer 3 and above of the OSI reference model, controlling all aspects of the IP network. In an unmanaged service (meaning the customer premises equipment [CPE]), IT staff generally owns and operates IP routers connected to the WAN service. The IT staff determines the endpoints of private-line circuits, or ATM and Frame Relay virtual circuits (VCs), through its orders placed with the service provider. The service provider is then responsible for setting up the VCs and delivering the traffic sent by the enterprise.

In Layer 2 IP/MPLS virtual private network (VPN) services, this relationship does not change. As shown in Chapter 1, "Assessing Enterprise Legacy WANs and IP/VPN Migration," this is because most Layer 2 IP/MPLS VPN services look like existing private-line, ATM, Frame Relay, or Ethernet connections.

However, in Layer 3 IP/MPLS VPN services, the relationship between the service provider and the enterprise changes to a shared relationship. These Layer 3 services require an integration of the two network environments at the network layer. This means that the service provider and enterprise must share the same common set of capabilities required by the enterprise, which makes the service's demarcation point slightly more complex. However, the benefits of the service generally outweigh the additional complexity.

It is possible to argue that there is no net gain in efficiency by outsourcing Layer 3 to a service provider. This generally has not been a successful argument. By building a service provider-managed core supporting multiple customers, the job of WAN optimization has to be performed only once, and that is good for all customers. Building separate WANs for each customer means that the same problems have to be solved by each enterprise to optimize WAN connectivity.