LANs /

Metropolitan technologies will benefit providers and users

By Mary Petrosky
Network World, 01/22/01

Service providers in the metropolitan-area network arena are in the midst of a technology explosion that promises to bring customers lower bandwidth costs, more flexible service provisioning and a wider range of service options.

Gigabit Ethernet, Multi-protocol Label Switching (MPLS), data-oriented SONET offerings, short-haul wave division multiplexing (WDM) and an emerging IEEE-defined packet ring protocol are among the technologies that are (or soon will be) finding their way into metropolitan provider networks. The technologies will help entrenched players and greenfield operators handle ever-increasing volumes of data traffic as well as expand their service offerings.

Gigabit Ethernet has grabbed the limelight recently, with metropolitan service providers such as IntelliSpace, Telseon, Yipes Communications and XO Communications rolling out Ethernet-based services in every major U.S. metropolitan market over the past year. These providers generally offer bandwidth in one-megabit increments up to a full gigabit per second, at prices less than half of what a customer would pay for a comparable time-division multiplexing (TDM) or SONET-based service.

This ability to buy only the bandwidth they need has been a key draw for customers. These Ethernet metropolitan service providers also typically can modify a customer's service - such as increasing bandwidth on a link - in a matter of hours. Several are developing Web-based provisioning tools to give customers dynamic control over their own services.

There's no doubt that Gigabit Ethernet has forever changed the economics of metropolitan services. And the advent of 10G bit/sec Ethernet will further cement Ethernet's place in the metropolitan market. With its WAN physical layer, 10G bit/sec Ethernet will easily interface to TDM and SONET/SDH infrastructures, simplifying its deployment in the metropolitan area.

But Gigabit Ethernet has drawbacks. For example, Ethernet is a data-oriented technology. A few providers, such as Yipes, have committed to supporting voice on their Ethernet metropolitan networks, but the quality of this service is as yet unproven. Current metropolitan implementations also require fiber-optic cabling end to end. Although there have been tremendous build-outs of fiber in metropolitan markets, the reality is that few customers have fiber to their buildings.

Consequently, copper-based TDM-oriented services will continue to be important for many customers - and their service providers. Fortunately, vendors such as Optranet, recently acquired by Extreme Networks, have developed technology that lets T-1 and DS-3 links function as the physical media for Ethernet frames. Extreme expects to ship the technology this quarter.

Another issue is that most metropolitan infrastructures are ring-based, built with SONET equipment. Service providers want to leverage their infrastructures but need a better way to support data traffic. Vendors of next-generation SONET gear are meeting this challenge by creating multifunction equipment and offering some innovative approaches.

For example, Appian Communications has a protection-switching scheme for packet services, dubbed Optical Data Protection (ODP), that can coexist on the same ring with SONET's unidirectional path-switched ring restoration mechanism. With ODP, a protected path can be shared among multiple entrance and exit points along the same SONET path in a ring, allowing for bandwidth efficiencies.

Although WDM has proved too expensive for metropolitan applications, prices for short-haul WDM are declining. Metropolitan providers can use this technology to squeeze more capacity out of the fiber they lease or own. Selective WDM, from Chromatis (now part of Lucent), also offers service providers an alternative way to exploit WDM.

MPLS also holds promise for the metropolitan area. MPLS gives service providers a new tool for provisioning VPNs, transparent LANs and other services.

On the horizon is a new data-oriented ring technology. Members of the recently formed IEEE 802.17 working group are defining a dual counter-rotating ring architecture, known as the resilient packet ring (RPR) protocol. RPR is media-independent; scalable; has distributed management, congestion control and protection mechanisms; and supports class-of-service capabilities. RPR would compete with SONET and Ethernet in the metropolitan area. An RPR standard could be finalized in two years, says the working group chair.

Customers are the ultimate beneficiaries of these technologies. Greenfield operators are pushing the price and provisioning envelope with Gigabit Ethernet, giving customers more data service options. Established providers can exploit their current ring architectures while migrating to more data-friendly infrastructures, and offer more competitive data and voice services.