Avici's turn to strengthen IP
 
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Avici Systems Tuesday became the latest router vendor to propose a way to make IP routing more resilient.
The company unveiled software for its Stackable Switch Router and Terabit Switch Router designed to deliver 99.999% reliability in a single router, which Avici says eliminates the requirement for service providers to install two routers at each point in their networks for redundancy. Avici is so confident in its implementation of routing resiliency that it is offering customers a service-level guarantee of 99.999% reliability or it will refund a portion of a service provider's maintenance fee.
Avici's rollout of its IPriori Non-Stop Routing (NSR) software comes on the heels of Cisco's Globally Resilient IP announcement, which followed Alcatel's introduction of ACEIS and Juniper Networks' unveiling of graceful restart. All four techniques seek to provide comparable levels of reliability to IP routing that service providers are used to from ATM, frame relay and circuit-switched TDM networks.
If IP is going to become the multiservice -- voice, video and data -- delivery infrastructure it's touted to be, it must achieve or surpass the levels of reliability common in older technologies, observers say.
Enhanced resiliency "represents a step up in the maturation of the IP protocol," says Tim Smith, an analyst at Gartner/Dataquest. "It's a good step forward in offering new capabilities, and it's important in the long term for next-generation multiservice IP networks."
Currently, service providers have to install two IP routers at each point of presence to attempt to attain the kind of dependability they get from single ATM, frame relay and TDM systems, Avici says. To that end, NSR is designed to provide transparent switchover within an Avici router to an active backup controller that takes over the control functions of the router. This can be executed without disrupting the routing protocol interactions with other routers, without resetting line cards, and without dropping packets, Avici claims.
NSR saves all pertinent routing states on backup servers at all times, and enables "hitless" software upgrades while interfaces keep forwarding packets. By contrast, "Headless Forwarding" approaches -- the term Avici applies to Cisco's GRIP and Juniper's graceful restart -- require interoperability with neighboring routers implementing competing IETF drafts.
These techniques continue forwarding packets even when the primary routing service has failed and cannot return, Avici says. This causes out-of-date routes to continue forwarding, leading to forwarding loops and disrupted or corrupted communication, the company says.
Cisco claims the amount of out-of-date forwarding information is negligible in GRIP, which is intended for the edge of the network where this occurrence has less impact, says Charles Goldberg, manager of product marketing. And "hitless," or in-service software upgrades, are currently not supported in Cisco's GRIP, but the vendor plans to address this apparent shortcoming in the future, he says.
NSR supports BGP, IS-IS, and OSPF routing protocols, and provides Layer 2 link redundancy through Avici's Composite Links technology, which bonds circuits together into a higher-speed virtual trunk for load balancing and redundancy. Cisco GRIP provides link resiliency by maintaining state on all Layer 2 sessions, which keeps them intact in case of routing protocol failure or reboot, Goldberg says.
Avici says its NSR technique is closer in similarity to Alcatel's ACEIS. But Alcatel is keeping details of ACEIS very close to the vest, so an apples-to-apples comparison remains difficult, Avici officials say.
Avici believes Alcatel is employing Mirroring Backup, whereby the backup control processor is a complete copy of the primary. The software is in lockstep with the primary, running all the same processes, saving the same state information, etc., so when the primary processor fails, the backup "seamlessly" takes over because it is at the same software execution point, with the same memory state.
But this is also the "Achilles' Heel" of mirroring, Avici says. Any software error that produces a failure of the primary control processor will also occur in the backup, the vendor says.
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