Cisco's Second String

Cisco Systems, Inc. http://www.cisco.com may have bought Cerent to get a foothold in the Sonet market, but it's still working on what amounts to a Sonet killer.

The killer in question is Dynamic Packet Transport (DPT), a technology that enables service providers to carry IP traffic directly over fiber in dual ring networks. It eliminates requirements for ATM and Sonet gear and makes more efficient use of fiber, according to the vendor.

Cisco's continuing interest in DPT was demonstrated last Friday, when it completed its acquisition of Pentacom Ltd. http://www.pentacom.co.il an Israeli startup that’s developed a hub for use in DPT networks.

The hub supports multiple physical rings and enables them to be brought together in larger virtual rings. This helps service providers adapt their networks to changing requirements, according to Graeme Fraser, vice president and general manager of Cisco’s metro IP business unit.

While Cisco strengthens its own DPT product line, it's encouraging other vendors to jump on the bandwagon. It's been pushing the IEEE and the IETF to set up study groups to develop standards for the underlying technology, known as the spacial re-use protocol (SRP). And it's encouraging semiconductor manufacturers to develop SRP chip sets. At least one, Conexant http://www.conexant.com, has already committed and two others are in the final stages of negotiations, according to Fraser. Some vendors of computers and networking equipment have also expressed an interest in developing SRP interfaces, he adds.

So, how does Cisco's DPT stack up against Cerent's box - or the growing number of other miniature Sonet muxes that have been announced in the past few months?

The answer is that it all depends on the application.

When routers are needed anyhow, DPT is an attractive solution. DPT has obvious applications in ISP POPs (points of presence), which typically comprise two sets of routers. On one side, multiple Cisco 7200 and 7500 routers handle access lines to customers, and on the other side, two or more Cisco GSR 12000 routers form a node on the ISP’s backbone. A DTP dual ring provides a scalable way of linking these routers. It also eliminates the ATM switches that are often used for this purpose.

Cisco, however, is also finding other applications for DPT. Cable operators are buildings rings of GSR 12000 routers to link together different hybrid fiber-coax networks, according to Fraser. The technology is also being used in straight-forward metro networks, particularly in Asian cities, he adds.

On the face of it, it’s hard to see the economic justification for using DPT for these applications, from two points of view.

First, DPT has only been implemented on Cisco’s routers at present, and these are expensive beasts. A fully equipped GSR 12000 can cost as much as $200,000 – around triple the cost of a small Sonet box. Fraser points out that users get a lot more for their money with a router. But it's questionable whether those extra functions would be called into use, experts say.

Second, DPT can’t match the performance of the new Sonet boxes. Right now, each DPT ring operates at OC-12 (622 Mbit/s) speeds and both rings can operate simultaneously. Cisco has announced OC-48 DPT developments, but they’re not shipping yet.

With Sonet gear, one ring is kept on standby – so it’s less efficient than DPT. However, current boxes already support OC-48 (2.5 Gbit/s) or OC-192 (10 Gbit/s) speeds. In other words, users get as much as eight times as much aggregate bandwidth, for as little as one third of the price.

Still, DPT offers other benefits that Sonet can’t match, according to Fraser.

In particular, it supports multicasting, which might explain its success in cable networks. Although Sonet supports multi-casting in theory, it would need operators to install Sonet cross-connects, which are even more expensive than routers.

DPT also eliminates the need to configure connections. “It’s plug and play,” says Fraser. This enables operators to automate service provisioning – a crucial consideration for a lot of carriers. By Peter Heywood, International Editor, Light Reading, http://www.lightreading.com
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