Riverstone believes in the old adage: if it ain't broke, don't fix it. Carriers have a large investment in ATM and Frame Relay networks that they have depreciated over time and that still have useful life left. More importantly, these networks support the carriers existing revenue generating customers.
However, the advent of Ethernet services is inexorable. The customer need for higher bandwidth and reduced communications costs can be met only with an Ethernet infrastructure. What is a carrier to do? If they make a sweeping change to their network to deploy Ethernet, they will have to spend an enormous amount of capital expenditure.
In addition, it forces them to operate parallel infrastructures during the time they migrate their customers from one to the other. Also, imagine the chaos that could result if the move does not go smoothly especially with a large corporation that has a multitude of sites like a financial institution or a diverse manufacturing company.
That is why Riverstone advocates an evolutionary approach to Ethernet services and VPLS. Customers who currently use circuit-based VPNs such as Frame Relay and ATM should not have to change every connection in every site in order to implement a new IP or Ethernet VPN for their corporate links. Customers who wish to use high-speed Ethernet services within a single metro area should still be able to connect and communicate with smaller sites that are happy with the lower bandwidth service they currently use.
We call this VPN Continuity and the key to providing it is VPLS. The Martini drafts specify how L2 traffic can be transported over an MPLS-enabled IP backbone. They include details for mapping Ethernet VLANs, Frame Relay DLCIs, and ATM Virtual Circuits to MPLS Label Switched Paths (LSPs) or tunnels. This provides the connectivity needed to provide existing VPNs over an MPLS core network.
However, this isn't enough. Customers want to mix and match different access methods but still have connectivity between, say, Ethernet sites and ATM sites. The extra mile that Riverstone goes is to provide this mapping between different access networks. The common denominator and the key to achieving this is the Ethernet VLAN. Since 95% of all customer traffic starts and ends on an Ethernet LAN, the Ethernet packet is the ideal common format that can be used to map between the various link layer standards so that the customer can receive and transmit the data in the format most convenient to them.
Customer traffic is uniquely identified into VLANs and the VLAN id is mapped into a corresponding MPLS label. And by using standard internetworking RFCs for translating Ethernet frames to Frame Relay packets and ATM cells, there is no need to change any equipment at the customer premise unless they wish to upgrade to a higher speed service.
As an example, consider a large bank. It uses Frame Relay to connect its branches and higher speed ATM connections for its headquarters and data centers. For security and disaster recovery reasons, it wishes to outsource and replicate its data centers in secure facilities but needs a high-speed LAN link between the data centers and HQ.
Also, some of the larger banks wish to offer new online, Web-based services to its customers, which places more bandwidth requirements on the network at unpredictable times. Additionally, the bank wishes to build an extranet with partners, such as building societies and insurance companies and stockbrokers.