Optical/IP Networks

Cisco's Resilient Ring Gets a Boost

There was a time when standards had to be agreed upon before semiconductor vendors could implement them, but those days are long gone, to judge from today’s announcement by Mindspeed Technologies, a division of Conexant Systems Inc. (Nasdaq: CNXT)

Mindspeed says that it’s developed the first chip to support the proposed IEEE 802.17 Resilient Packet Ring (RPR) standard (see Mindspeed Offers Packet Ring Solution), a technology that aims to give low-cost Ethernet networks some of Sonet’s self-healing capabilities (see IEEE Tunes Ethernet for Telcos).

But guess what? The Institute of Electrical and Electronics Engineers (IEEE) hasn’t even started discussing the proposed RPR standard. The first meeting is planned for March.

In fact, Mindspeed’s chip, the CX29950 RingMaker, implements technology called the spacial reuse protocol (SRP) that Cisco Systems Inc. (Nasdaq: CSCO) has been trying to get standardized for a couple of years. It forms the basis of Cisco’s Dynamic Packet Transport (DPT) equipment that’s already in use in Internet service providers’ points of presence, cable networks, and (oddly enough) some metropolitan area networks in China (see Cisco's Second String).

So, how can Mindspeed wave a magic wand and turn its SRP chip into an RPR one? And is this some sinister Cisco standards plot in the making?

Mindspeed says it’s nothing of the sort. It acknowledges that it might need to tinker with its chip to bring it into line with whatever standard comes out of the IEEE. “We will make any modifications required,” says Lauren Schlicht, product line manager for Mindspeed’s broadband internetworking systems unit.

However, Schlicht isn’t expecting major changes, because the IEEE is likely to limit the scope of the RPR standard to bridging between rings. The upshot is that proprietary technologies, such as Cisco's SRP, will continue to be used within rings. Carriers accept that they won't be able to mix equipment from different vendors on the same ring, according to Schlicht. Cisco’s biggest competitor in this field, Nortel Networks Corp. (NYSE/Toronto: NT), has its own ring technology called Optera Packet Edge (see http://www.nortelnetworks.com/products/01/optera/packet_edge/doclib.html for details). Right now, Nortel has embedded its ring technology in some of its products but hasn’t encouraged other vendors to adopt it in the way Cisco has with SRP.

Schlicht says that Mindspeed is already working with nine vendors (in addition to Cisco) that are using its CX29950 RingMaker to develop equipment. So far, only one of them -- Riverstone Networks -- has announced an SRP-based product.

All the same, nine vendors developing SRP-based products equate to a fair amount of support for whatever Cisco submits to the IEEE working group developing the RPR standard.

One fly in the ointment could be that the current version of Cisco's DPT has a fundamental problem -- that it won't support DiffServ (differentiated services), a crucial standard for enabling service providers to offer different grades of service at different prices, according to Juha Heinanen, the CTO of Telia Finland (a subsidiary of Sweden's Telia AB) and an Internet infrastructure guru.

The problem stems from the fact that DPT only supports two traffic classes that have a strict priority relationship, according to Heinanen. "DiffServ requires more than two traffic classes, each with its own configurable buffer space and scheduling weight," he says. "Also, within each class, it should be possible to assign packets a different level of drop precedence." This isn't possible with DPT.

Heinanen also points to problems with the way in which DPT ensures that attached equipment doesn't hog access. "DPT's FDDI-like, node-based fairness concept would need to be redesigned in order to make RPR DiffServ compatible," he says. -- Peter Heywood, international editor, Light Reading http://www.lightreading.com

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