| Delivering Layer 2 VPNs over an IP/MPLS infrastructure has several benefits, including the following: Common infrastructure No new infrastructure is required to offer Layer 2 VPNs. The same IP/MPLS network can be used to deliver Layer 3 VPN services and Layer 2 VPN services. This is extremely cost effective when compared to building out completely new networks with one for Layer 2 and another for Layer 3. With this, equipment as well as operations costs can be duplicated. However, many providers have existing separate networks that provide both Layer 2 and Layer 3 services, respectively. Both those networks can be migrated to a converged network, based on packet infrastructure, for cost-effective delivery of Layer 2 and Layer 3 services. This is the reason many service providers are evaluating or migrating to the converged networks. Convergence is a hot topic. Many issues must be considered when planning a converged network, though. Most of them relate to three categoriesnamely, technical, business, and operational issues. Installed networks are also one of the inhibitors to a single IP/MPLS network for Layer 2. Many providers have investments that must remain in use to complete the amortization of the existing Layer 2 equipment, and until the value of this equipment is fully depreciated, providers are reluctant to take on the added cost of new equipment and to lose the write-offs of installed equipment. However, most providers should see the majority of installed-base hardware fully depreciated within the next 1224 months because minimal new investment has been made in Layer 2 switches in the past 12 years. Service flexibility Because Frame Relay and ATM networks allow service providers to offer FR and ATM service only, if the same service provider wants to offer Ethernet services, the service provider must undertake a completely new build-out of Ethernet network. As the service portfolio expands, the network must also expand in the same way, resulting in the significant expansion of management products and operations costs. Using an MPLS network allows the SP to offer Ethernet, Frame Relay, ATM, PPP, or HDLC service on the same network without building a completely new network. As the service portfolio expands, more line cards might need to be added to the existing IP/MPLS-capable network devices for connecting the correct transport type. Value-add services Using MPLS-based Layer 2 VPNs, many new service types can be offered. For example, with PPP over MPLS or HDLC over MPLS, a new service can be created equivalent to a leased linea virtual leased line. This service emulates a PPP or HDLC link across the IP/MPLS network. By combining this functionality with MPLS traffic engineering and QoS, a tight SLA can easily be offered for this service. A physical leased line does not offer any protection against the failure of network core components. In contrast, the virtual leased line service can be protected against link, node, and path failures using MPLS TE and MPLS Fast Reroute. A service provider can show value by offering a PPP- or HDLC-protected link capability with the bandwidth guarantees to mimic leased lines. Back-haul services PPP/HDLC over MPLS can be used for back-hauling PPP connections from remote pops to central termination points in the network. For example, a national provider in the Asian Pacific is back-hauling DSL PPP connections from remote POPs to a central POP that houses all the user authentication capability. This means the national provider need not provide all the authentication and termination equipment at remote pops, thereby reducing the operations costs by using the available technology to back-haul to a few central locations and administer them through the central points. Remote peering Using interworking and virtual leased line capability, remote peering can be offered as a service to local regional providers. For example, one national provider in Europe uses PPP-to-Frame Relay interworking to offer peering capability on a PPP connection to small regional service provider with global service providers on Frame Relay or ATM connections. This is done without requiring the regional providers to physically buy a connection to the global gateway point. This results in cost savings for the regional providers, as well as a new service for the national provider. Wholesale trunks Using AToM, point-to-point trunks can be sold for ATM and or Frame Relay networks. This is a useful application for selling central office-to-central office (Co-to-CO) voice trunks. In the enterprise environment, PBX tie lines, previously carried through ATM service, can now be carried across the converged network, which provides both Layer 3 and Layer 2 capability. Transparent LAN services Ethernet connectivity is popular for metro region transport. VPLS allows a service provider to offer Layer 2 Ethernet service in a metro region connecting the enterprise. Alternatively, the enterprise can either deploy or buy Ethernet connectivity to branch sites and maintain control over its own routing and addressing plans. Leverage the high-speed packet core Any Layer 2 network cannot be expanded natively to a core bandwidth of OC-48 or greater due to limitations of available hardware and the technology. For example, no Frame Relay networks exist with OC-48 core bandwidth. In addition, until recently no ATM OC-192 interface was available from any vendor. The maximum speed for Ethernet is 10 Gbps. When Layer 2 connections are aggregated, the core trunks must be high bandwidth to carry aggregated traffic between PEs. Using an IP/MPLS network, higher bandwidth core networks can be built up to OC-768 and large amounts of Layer 2 and Layer 3 traffic can be aggregated easily.
The real benefit of Layer 2 VPNs over MPLS comes from the overall cost savings due to the possibility of building a converged backbone. Otherwise, for multiple services, multiple networks must be builtwhich impacts the bottom line. With the planning of various service providers to build a next-generation network (NGN) that converges Layer 2 and Layer 3 services, L2VPN becomes a critical service as part of the NGN portfolio. In addition, IP/MPLS provides the cost savings needed to build one infrastructure. |
