The skinny on VPLS

Virtual Private LAN Service technology tries to overcome some of the inherent shortcomings of WANs, namely complexity, limited bandwidth and application performance degradation.

VPLS combats complexity by presenting corporate networks with an Ethernet interface they plug into their routers or switches and then simulating a LAN routing environment among corporate sites.

Because access to VPLS is Ethernet, bandwidth can scale in increments of 1M bit/sec up to the speed of the wire, giving customers the option to buy the bandwidth they need to provide the performance they want.

Performance degradation can be overcome by use of QoS features of Multi-Protocol Label Switching (MPLS), VPLS' underlying backbone technology.

VPLS combines the Layer 2 nature of Ethernet with Layer 2 MPLS label-switched paths to create the impression of a circuit known as a pseudo-wire. These customer pseudo-wires are mapped through MPLS label-switched paths across the carrier backbone.

Traffic from individual servers and desktops in customer networks is switched based on their media access control addresses, with the providers' edge routers keeping track of them and making sure traffic from them is switched along the appropriate paths.

VPLS defines the encapsulation of traffic from the Ethernet access segment of the network to the MPLS core to maintain service quality needed to maintain acceptable application performance.

By creating a fully routed environment, VPLS provides any-to-any, fully meshed networks. To create similar networks using dedicated circuits, frame relay or ATM involves complex network design and multiple permanent virtual circuits, which can be expensive.

Simplifying fully meshed networks for customers is a benefit of VPLS, but it requires work on the carrier's side to set up the full mesh of label-switched paths among its edge routers. It also requires provisioning each customer's service within these paths. Several groups are working on standards for managing VPLS networks to make the task easier for service providers.

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