RPR proposals converge

The IEEE 802.17 Resilient Packet Ring working group has agreed on a baseline draft of the RPR standard, the first major milestone in reaching ratification.

Even more significant, though, is that the draft - dubbed Darwin, to signify an evolutionary event - merges two opposing proposals led by Cisco Systems Inc. and Nortel Networks Corp. There was much contention within the working group due to the diverging proposals, disagreements that threatened to further delay progress on the RPR standard.

But Darwin received more than 75 percent approval from working group participants during a recent meeting in Orlando. Still, a final RPR standard isn't expected for another 15 months.

Darwin represents a merger of the Cisco-supported "Gandalf" and the Nortel-supported "Alladin" proposals, and contains bandwidth management mechanisms advocated by both. Darwin also retains the same basic structure for congestion signaling used by Cisco's Spatial Reuse Protocol (SRP) technology - the foundation of Gandalf - but changes were made to congestion detection techniques.

In addition, Darwin's protection mechanisms are a combination of Gandalf's packet-wrapping scheme and Alladin's packet-steering mechanism. Packet wrapping simply means that packets travel in the opposite direction in the event of a failure. Steering involves notifying all nodes of a failure and subsequently directing traffic away from a fault.

While Gandalf originally proposed using only packet wrapping for protection, Darwin uses packet steering as the default protection mechanism, with packet wrapping as an optional mechanism.

Finally, while packet formatting also retains some SRP characteristics, other adaptations have been made, including the addition of a header error-checking field.

Work still needs to be done in the area of topology discovery and what speed - 2.5G bit/sec, 10G bit/sec - RPR will be adapted to.

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