Service Provider

The benefits of an IP Networks are well understood:

rapid delivery of rich multimedia services, increase efficiency, enhanced resource management, carrier class resilience and availability, and superior service and network control – a complete business transformation. Flexible infrastructure becomes essential to meet those goals. The Metro Ethernet based Carrier Ethernet should support all residential quadruple-play services and standard Layer 2 MEF point-to-point and multipoint business services plus Layer 3 IP MPLS/Multicast VPNs for business customers.

The two most deployed transport architectures are native 802.1ad (or QinQ) and MPLS. The native 802.1ad uses S-VLAN for service delivery and STP for resilience support. Before the 3-play and mission critical VPN are transported by the Carrier Ethernet, this architecture was widely deployed since double tagging expands the services significantly beyond what 802.1q supports. However, the nature of the slow convergence of STP is challenged if voice and video services are added. It also constrains the network intelligence due to the L2 limitation. For instance, bandwidth management can’t be supported without a topology aware NMS. On the other hand, MPLS Carrier Ethernet Networks have been built by major SPs in the world to roll out triple-play services for their residential and enterprise customers.

The capabilities of NGN Carrier Ethernet will transform the legacy Carrier Ethernet from the transport Ethernet to service enabled Ethernet. The IP NGN based Carrier Ethernet architecture is that multiple Layer 2-3 network technologies are used to provide optimal flexibility for current network and next-generation service offerings. These technologies and protocols include native Ethernet VLAN(802.1q), 802.1ad, EoMPLS, Layer 3 PIM-SSM, MPLS VPN, and H-VPLS. This allows the Metro Ethernet to support a broad range of applications while minimizing capital and operating expenses associated with the network infrastructure.

The NGN CARRIER ETHERNET architecture also achieves carrier-class resilience and troubleshooting requirements. Standards-based OAM end-to-end across the access and core switches allow to manage Ethernet connectivity all the way to the customer premises. This includes 802.1ag for service verification, 802.3ah for link-layer troubleshooting, and E-LMI for service status and auto provisioning of customer equipment. The architecture provides a highly available solution that supports sub-second multicast convergence and link restoration across the end-to-end network. Using FRR for the aggregation and distribution EoMPLS tunnels, 50 ms restoration can be achieved. This features enables to deploy NGN voice with carrier-class protection..

Layer 3 VPNs

In a Layer 3 VPN, the routing occurs on the service provider’s routers. Therefore, Layer 3 VPNs require more configuration on the part of the service provider, because the service provider’s PE routers must store and process the customer’s routes.

Layer 3 VPNs are based on RFC 4364, BGP/MPLS Virtual Private Networks. This RFC defines a mechanism by which service providers can use their IP backbones to provide Layer 3 VPN services to their customers. The sites that make up a Layer 3 VPN are connected over a provider’s backbone.

VPNs based on RFC 4364 are also known as Border Gateway Protocol (BGP)/MPLS VPNs because BGP is used to distribute VPN routing information across the provider’s backbone, and MPLS is used to forward VPN traffic across the backbone to remote VPN sites.

The interfaces between the PE and CE routers of a Layer 3 VPN can be configured to carry IPv6 traffic. IP allows numerous nodes on different networks to interoperate seamlessly.

Layer 2 VPNs and VPLS

Implementing a Layer 2 VPN on a router is similar to implementing a VPN using ATM or Frame Relay. However, for a Layer 2 VPN on a router, traffic is forwarded to the router in Layer 2 format. It is carried by MPLS over the service provider’s network and then converted back to Layer 2 format at the receiving site. The security and privacy of an MPLS Layer 2 VPN are equivalent to those of ATM or Frame Relay.

Virtual private LAN service (VPLS) is designed to carry Ethernet traffic across an MPLS-enabled service provider network. In many ways, it works like a Layer 2 VPN. The key difference in VPLS is that packets can traverse the service provider’s network in a point-to-multipoint fashion. In effect, the VPLS domain simulates and provides similar connectivity to an Ethernet domain across the MPLS backbone.

MPLS Layer 2 VPNs and VPLS can make use of BGP to distribute the VPN connectivity information. This is in common with Layer 3 MPLS VPNs, giving significant administrative advantages when both L3 and L2 VPNs are required for different services on a common backbone network.

Layer 2 VPNs and VPLS services are so far not widely used in Mobile Packet Backones, but Pseudowires that provide discrete point-to-point transport links for legacy services are increasingly popular.

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