RPR Group May Swim Through 'Flooding'
The 802.17 standard got ratified by the IEEE late in June (see 802.17 Standard Completed). The catch is that, while the standard is complete for Layer 3 implementations, it doesn't pack the same punch when used at Layer 2.
"If you want an 802.17 ring to act as a bridge and do MAC-level forwarding, right now you lose some of the spatial reuse elegance of RPR," says John Hawkins, chair of the Resilient Packet Ring Alliance and senior marketing manager at Nortel Networks Ltd. (NYSE/Toronto: NT). Spatial reuse lets multiple traffic streams use fractions of a ring simultaneously.
This becomes a problem at Layer 2 because of "flooding," which occurs when a packet carries a MAC address that's not in a node's forwarding database. Uncertain what to do, the node broadcasts the packet everywhere it can -- all the way around the ring, in the case of RPR -- to determine which node is the destination. This doesn't come up in Layer 3 cases because each node has more complete knowledge of the surrounding world.
The problem would be solved by a technique called advanced bridging. This was originally considered for inclusion in the standard but was dropped after the 802.17 group finished compromising between two competing drafts (see RPR Moves Forward). In the end, the group saw bridging as "more of an improvement, rather than something you had to have," says Martin Green, product manager in Cisco Systems Inc.'s (Nasdaq: CSCO) Advanced Routing Technology business unit.
Corrigent Systems Inc., Luminous Networks Inc., and Nortel likewise agreed with the decision, but it still created some controversy -- at least on Light Reading's message boards. The working group will decide next week whether to tackle advanced bridging, and it's not clear whether enough interest will surface. "[Advanced bridging] will be, I think, the main issue on the table, but that issue is relevant to only some of the RPR implementations out there," says Gady Rosenfield, director of marketing at Corrigent.
Regardless of the outcome, some basic Layer 2 abilities will be added to 802.17, Hawkins says. Work is underway on what's likely to be called 802.17a, which would make RPR fit in with the basic Ethernet bridging rules of IEEE 802.1.
— Craig Matsumoto, Senior Editor, Light Reading
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