Riverstone seeks to strengthen metro Ethernet

While vendors debate the definitions of metro Ethernet specifications within standards groups, they continue to develop and market their proprietary alternatives outside the standards bodies.

Riverstone Networks Inc., for example, has developed a technology designed to make Ethernet more resilient in the metro area. The company’s Rapid Ring Spanning Tree Protocol (RRSTP) is based on the IEEE 802.1w Rapid Spanning Tree Protocol for Ethernet reconvergence, Riverstone claims, and is also positioned as a “mini” version of the IEEE 802.17 Resilient Packet Ring (RPR) specification for SONET-like restoration of Ethernet.

But unlike IEEE 802.1w and RPR, which are designed for large regional networks, RRSTP is optimized for metro access where Ethernet access rings are increasingly being deployed, Riverstone says. And Riverstone claims it is seeking to standardize RRSTP for the metro access arena.

Still, some analysts are labelling RRSTP as yet another proprietary metro Ethernet protection scheme that may confuse buyers and render emerging standards – especially RPR – irrelevant as vendors haggle over definition while their specific alternatives build market share and “mind share”.

“I think I’d prefer that they concentrate their energy on getting the RPR standard through and getting through the deadlock that’s happened with the Nortel camp versus the Cisco camp,” says Marian Stasney, senior analyst of Carrier Convergence Infrastructure for The Yankee Group in Boston. Nortel and Cisco are ostensibly two of the key vendors at odds over the definition of RPR.

RRSTP essentially breaks down the metro access network into separate rings, according to Riverstone. Each ring runs its own instance of the proprietary technology, which reduces the number of nodes RRSTP must monitor because the technology is isolated on a particular ring, Riverstone says.

By breaking the metro access network into separate rings, RRSTP also avoids the lengthy reconvergence times associated with IEEE 802.1w, which takes between one and 10 seconds to fail over, says Tim Wu, Riverstone technical marketing director. Riverstone says that fault detection and failover can now occur in 400 milliseconds.

Though this is eight times slower than SONET’s 50-millisecond recovery, it’s adequate for metro access requirements, Riverstone claims. SONET-like resiliency isn’t as crucial in the access network as it is in the regional transport network because line rates are typically slower than regional transport or core, the company says.

RRSTP uses the same signalling algorithm that IEEE 803.1w uses to detect failures in last-mile Ethernet rings. Once a failure is detected, the algorithm simply “tells” traffic to move in the opposite direction on the ring.

Wu says RRSTP also works with Multiprotocol Label Switching (MPLS) by offering a backup circuit for Label Switched Paths (LSP). When RRSTP is used in this manner, Wu says carriers get the benefit of overlapping protection schemes.

The MPLS-based service features of RRSTP are currently in beta and will be available sometime in 2002, Wu says.


Not everyone is impressed with Riverstone’s claim of better protection with RRSTP, though. Yankee Group’s Stasney doesn’t think the technology should be positioned as a protection mechanism.

IEEE 802.1w allows for the addition of two more ports for faster reconvergence, a feature not included in RRSTP, she notes. And even though the Metro Ethernet Forum is pitching MPLS as a metro Ethernet protection scheme, it was never designed for that purpose and shouldn’t be used as such, she says.

“MPLS is not a protection scheme, I don’t care what the (forum) says,” Stasney says. “Carriers are saying that it’s strictly a traffic engineering technology, and I agree with that. That’s what it should be used for – end of discussion.”

Despite the proprietary nature of RRSTP, Riverstone says it is “complementary” to RPR, and can interoperate with SONET-based regional networks. Riverstone is currently pursuing a standard around RRSTP both within the IEEE and the Metro Ethernet Forum.

Stasney says this standards effort is key to the success of RRSTP.

“I’m concerned that this is a proprietary technology,” she says. “The effort to get this standardized promotes interoperability, and that’s always a good thing.”

Riverstone claims RRSTP can help save service providers money by optimizing ring topologies for Ethernet. IEEE 802.1w is designed for mesh networks.

Using RRSTP, carriers can typically see 60 percent to 100 percent savings in fibre lease costs, depending on the particular network and if that network is a partial-mesh or full mesh, Riverstone claims.

The RRSTP feature is currently available on all of Riverstone’s Ethernet interfaces and starts at US$3,000.

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