Foreword

If we have learned one thing from the plethora of wireline connectivity technologies, it is that they change constantly. Over the years, while Ethernet was taking over enterprise networks, Frame-Relay, ATM, and SONET/SDH ruled the service provider domain. Attempts were made to unify these technologies, but in the end, the result was independently operated networks, with some interoperability at the edges.

Consequently, the infrastructure of the service providers was expensive and lacked consistency, and a massive transformation was long overdue. IP/MPLS, the emerging technology of the 1990s, provided an abstraction that enabled service providers to interconnect their disparate networks, while endowing that same network with a uniform set of characteristics that was independent of the underlying carrier technology: QoS awareness, traffic-engineering, and fast recovery times in the face of outages. However, MPLS wasn't multi-protocol enough, and needed a killer app to make it universally applicable.

Enter pseudowire technology: Virtual Leased Lines (VLL) and Virtual Private LAN Service (VPLS). Based on the MPLS architecture, pseudowires allowed a service provider to abstract out the idiosyncrasies of wired technologies. This allowed them to continue to support various connectivity technologies at the edge of their networks to customers while migrating to a modern architecture in the core. Customers with both IP and non-IP traffic could now be connected across a multi-service, multi-protocol network.

MPLS absorbed the best of the Layer 2 capabilities of the network infrastructure, but the story didn't stop there. While VLL addressed the problems of a transition to a modern networking architecture, VPLS typified the best of the connectivity models. Ethernet, as a Layer 2 technology, was just another technology like Frame-Relay or ATM. Ethernet, as a network model, delivered the ease-of-use that has made it the choice for enterprises.

VPLS is not simply an Ethernet emulation — it is a connectivity model that abstracts a LAN. It can be used as a VPN service, connecting multiple customer sites together, providing them the ease-of-use and consistent feel of a single Ethernet network. But it can just as well be used as an infrastructure technology, providing the service provider with a highly reliable LAN service spanning a larger geographic area than has been covered by customary Ethernet networks.

I hope that as you read this book, you will appreciate the opportunities IP/MPLS VPNs present to address the connectivity and architectural requirements of customers.

Vach Kompella

Director, MPLS Development

Alcatel-Lucent