Metro's middle ground

Everyone seems to be worried about metropolitan area networks. So much demand coupled with too little connectivity has created a conundrum for service providers and vendors. For many, trying to force-fit long-haul technologies into metro environments has been the answer, but it isn't necessarily the best one.

Service providers that primarily hold long-haul assets feel far more comfortable bringing familiar technologies such as Sonet and dense wave division multiplexing (DWDM) into the metro. But those technologies are not as scalable and flexible as the metro requires. With Sonet's inflexibility and ATM's complexity — not to mention that it wasn't designed for IP — costs can go up, and efficiencies can be low for providers that implement those technologies anyway.

In contrast, some providers have opted for Ethernet in the metro because the technology can deliver high bandwidth at low cost. But Ethernet's enterprise roots may make it less capable of handling issues such as latency and leave service providers unable to guarantee bandwidth rates.

As a result, a group of equipment vendors is developing a new standard called resilient packet rings, or RPR, designed specifically to meet the needs of the metro environment by combining capabilities of Sonet and Ethernet. So far, the group, which consists of Cisco Systems, Dynarc, Latern Communications, Luminous Networks and Nortel Networks, has gotten approval from The Institute of Electrical and Electronics Engineers (IEEE) standards association to form a Resilient Packet Ring Working Group.

“[RPR] offers better utilization of bandwidth traffic management and is an intelligent way to manage a ring,” said Frederic Thepot, vice chairman of the RPR Alliance and director of business development for Dynarc.

The networks currently deployed in the metro area are not optimized or scalable to handle the needs of that environment, according to Thepot. While Sonet has the obvious benefits of high resiliency and low latency and Ethernet offers high bandwidth at a low cost, “the question is how to have the best of Sonet and Ethernet,” Thepot said.

RPR has a simplified network design that scales to optical performance while providing Sonet-like resiliency, Thepot added.

Using RPR, only traffic sent to or destined for a particular node must be processed by a router. Other traffic circumvents the router, theoretically easing the router's load. Because the technology uses a distributed ring network, it requires half the number of ports to provide the same amount of resiliency found in centralized switched networks with redundant paths.

Additionally, RPR uses all fibers in a ring concurrently to enable better bandwidth usage, said Lloyd Green, senior director of marketing for Dynarc.

But while RPR's capabilities make sense, service providers don't appear to be holding their breath for the technology, which is at least a year away.

“Right now, we are focusing on dramatically increasing capacity at the core,” said Vesna Swartz, vice president of marketing for Telseon. “We are starting to deploy metro WDM at the core because it is less expensive than DWDM in the long haul.” Telseon is not discussing RPR, Swartz added, noting that instead, the company is focusing on deploying 10 Gb/s Ethernet in its network this year.

Another provider, Yipes Communications, is using gigabit Ethernet with DWDM. Yipes also is looking to deploy 10 Gb/s equipment this year, said Robert Valdez, chief financial officer at Yipes.

Although RPR has yet to become a standard, “it does look very promising,” Valdez said.

The technology needs some work and successful trials before it will take off, but “it really is a good middle ground for service providers,” said Doug McEuen, senior marketing analyst for Pioneer Consulting.

With Sonet and Ethernet in for the long haul, so to speak, a technology that takes the best aspects of each is not a bad idea, he added.