Riverstone proposes Ethernet ring scheme
By Craig Matsumoto
EE Times
(11/05/01, 4:19 p.m. EST)
SAN MATEO, Calif. — Riverstone Networks Inc. (Santa Clara, Calif.) unveiled Monday (Nov. 5) a home-brewed scheme for improving Ethernet resiliency in metropolitan access rings.
Like the resilient packet ring standard being crafted by the IEEE-802.17 working group, Riverstone's technology, based on the Rapid Ring Spanning Tree Protocol (RRSTP), tells the network what alternate routes to use when a connection fails. The two are aimed at different networks, however: RPR is for the metro core and can accommodate Sonet, while RRSTP is strictly for metro access rings that run Ethernet.
Early metro Ethernet deployments used a mesh topology, but others have begun using rings, which require less fiber. One such carrier, Dacom Corp. (Seoul, South Korea), is one of the three RRSTP users announced by Riverstone this week. French carrier CompleTel Europe NV (Paris) and service provider Intellispace (New York) also plan to use the technology, Riverstone said.
RRSTP is based on Ethernet's spanning-tree protocol, which maps all network nodes into a "tree" of usable connections. If a connection breaks, the network redraws the tree.
But to obtain the kind of resiliency that service providers demand, that redrawing process needs to be speeded up. The original protocol takes several seconds to reconstruct the tree, and the newer Rapid Spanning Tree protocol takes 0.5 second.
RRSTP takes advantage of the fact that a ring has only two paths exiting from each node, clockwise and counterclockwise. This cuts down on the routing possibilities and allows the tree to be redrawn more quickly. Tests so far have produced recovery times of less than 400 milliseconds, said Tim Wu, Riverstone technical marketing director.
"It's not the performance of Sonet, but for data networks it's high resiliency," he said.
The protocol handles only one ring, but that's suitable for service providers, Wu said. For assuring connections across an entire network of rings, other standards such as multiprotocol label switching, with its fast failover, are more appropriate, he said.
Dacom and CompleTel will use RRSTP in Ethernet rings currently under construction. |
