RPR standard, products progress

Products compliant with the IEEE 802.17 Resilient Packet Ring standard are expected to be developed in earnest shortly after Christmas, according to officials of the RPR Alliance, a body charged with promoting and educating the public on the standard.

The IEEE working group developing the standard, which is intended to enable efficient and reliable packet data networking in metropolitan-area networks, will not accept any modifications to it after September, alliance officials say. That means silicon vendors can start baking it into hardware for systems vendors even though the standard isn't expected to be complete until the Fall of 2003, alliance officials say.

"We expect significant (product development) activity soon after Christmas," says Robert Love, president of the alliance and vice chairman of the 802.17 working group.

Prestandard RPR products are already being deployed by several service providers, including Bell Canada, WorldCom Inc., Sprint Corp. and China Netcom Communication Group Corp., alliance officials say. Vendors of these products say they will only require a software upgrade to make them compliant with the final standard.

But RPR may be a tough sell given today's capital spending environment, carriers' preoccupations with protecting current investments, the familiarity of current technologies, like SONET, and its recent advancements in handling data traffic, like Ethernet. Love, however, characterized RPR as a "completing, not competing" technology to Ethernet and SONET that can provide compelling operational and capital expenditure savings over both.

"Carriers are desperate to increase revenue," he says. "The value proposition of RPR shows them how to do that. They can't afford not to be doing this."

For Ethernet "completion," RPR switches perform no segmentation or reassembly when translating IEEE 802.3 Ethernet frames to 802.17; they merely encapsulate the frame in an RPR header that contains a time-to-live field and bits for sending traffic in either an east or west direction. RPR is also less expensive than Ethernet, alliance officials claim. Its ring topology uses half the optical ports of Ethernet's hub and spoke or mesh architectures, they say.

Indeed, Corrigent Systems, a maker of RPR switches and a member of the RPR Alliance, claims that service providers can save thousands of dollars in optical port costs by deploying 802.17.

"The cost savings are dramatic," says Nigel Cole, Corrigent vice president of business development and an RPR Alliance director. Corrigent claims that in some cases, RPR capital expenditures can be less than half that of point-to-point optical Ethernet and Ethernet-over-SONET.

RPR is also more deterministic and reliable than Ethernet, alliance officials claim. RPR provides edge-to-edge quality of service by reserving and guaranteeing bandwidth via committed information rates for high priority traffic, like voice and fairness queuing algorithms. Ethernet cannot provide these bandwidth guarantees, they say.

For resiliency, RPR can provide millisecond restoration from network outages; Ethernet requires seconds, even when using Multiprotocol Label Switching fast reroute or redundant label switched paths, as the Metro Ethernet Forum is proposing, alliance officials say.

For SONET compatibility, RPR uses the SONET/SDH PHY, and can carry TDM and other SONET-based services, officials say. RPR also supports virtual concatenation, officials say, which maps the payloads of various services into smaller bandwidth increments to make better use of higher speed pipes.

In SONET, virtual concatenation uses point-to-point 1.5M bit/sec VT 1.5 and 52M bit/sec STS-1 signals as the payload building blocks for filling up OC-48 or OC-192 trunks. RPR virtual concatenation, however, supports multicast and is not bound by VT1.5 constraints, analysts say. Virtual concatenation and generic framing protocol (GFP) were devised to offer more bandwidth-efficient ways of packing Ethernet traffic into a SONET/SDH transport network. Some have suggested that GFP and virtual concatenation on existing SONET networks will render RPR irrelevant - but RPR officials counter by stating that SONET is still inefficient for transporting packet-based services.

SONET requires N new point-to-point circuits for each added node; circuit capacity engineering for efficiency; and a large number of TDM interfaces on IP devices, alliance officials say.

But working in SONET's favor are its ubiquity, familiarity and the current reticence of service providers to spend money. Vendors developing "pure" RPR switching and transport systems that do not support legacy SONET infrastructures will find particularly tough sledding, analysts say. "Pure RPR with no support for SONET is dead," says Michael Ladam of Stratecast Partners. "I don't think that's going anywhere. It has no buyers today."

Vendors proposing hybrid RPR-over-SONET switches that support Ethernet media access control bridging will have the best chances for success in the metro market, he says.

"There's potential for RPR to be a winner or a dominant player in the access network," Ladam says. "But it's going to be a while, and SONET has demonstrated much more (market) resilience than people thought it had. New SONET components will drive the cost down and provide efficient transport for data."

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