Metro optics

The push for bandwidth in the metropolitan market has some carriers deploying dense wave division multiplexing. Claiming "fiber relief," these carriers boost bandwidth, but not necessarily for the right reasons. Data, which is kludgy in the telecom environment, continues to infiltrate networks, so carriers are ramping up using technologies that are near and dear to their hearts and legacy investments.

However, metro market needs are drastically different from long-haul needs, said Hugh Martin, president and CEO of upstart Optical Networks.

"I don't think DWDM as a solution is what the metro market needs," he said. "What it needs is a metro network solution." That network combines the reliability, survivability and protection characteristics of telecom networks with the flexibility of enterprise networks.

In its endeavor to produce a "true optical network," Optical Networks surveyed its customers' customers: enterprises and end users, Martin said.

"We identified eight specific requirements you've got to fill if you want to be a metro player," he said. Vendors in this market have to provide a low-cost, scalable, high-capacity, data-centric solution with dynamic provisioning, manageability, survivability and service transparency.

Optical Networks hopes to fit the bill. The company developed a WDM product that incorporates an optical network operating system and an optical link management protocol. The system lets customers create point-to-point, ring or meshed networks with bidirectional line switched ring-like protection. It performs optical add/drop and cross-connect functions, and carriers can increase channel count in increments of three.

Also, routers will be able to communicate with the network and request immediate provisioning of links, Martin said.

The concept is similar to Cisco Systems' Dynamic Packet Transport solution, which also brings LAN-like capabilities to the metro market.

Time division multiplexing is expensive and inefficient for data transport, noted Tony Bates, director of marketing in Cisco's optical internetworking business unit. With DPT, Cisco wants to "turn the paradigm away from point-to-point and back to shared media," he said The DPT architecture allows data to traverse a big pipe and performs statistical multiplexing.

DPT uses a Cisco-developed Layer 2 technology, called the spatial reuse protocol (SRP). It embeds the Layer 2 media access control protocol information into the payload of the Sonet frame. The DPT ring comprises two rings, each carrying the control information for the other ring (see figure).

SRP can transfer traffic on different spans of the ring, and it strips packets at the destination point instead of the point of origin. All nodes on the ring are equal unless a priority is invoked. It operates with Sonet/SDH, but carriers can also plug fiber directly into the router.

"This technology pushes the [Internet protocol] functionality much closer to the customer and to the edge of the network, and we do this in a data-centric manner," Bates said. "It's the marriage of the good properties of Sonet/SDH with those of data."

One key difference between the two approaches is the restoration method, said Mathew Steinberg, director of optical networking at RHK. Optical Networks provides protection at the optical layer, where Cisco provides protection in a Layer 2 implementation. Carriers will have to determine where they think they can get the best restoration in their network for the type of service they are carrying, he said.

DPT allows carriers to build rings with routers, in much the same fashion as building a Sonet ring, Steinberg continued. "Optical Networks is doing optical layer protection so carriers can connect Sonet devices, [asynchronous transfer mode] switches or routers, gigabit Ethernet switches, [enterprise systems connection] devices or any other protocol or bit-rate up to 2.5 Gb/s. What they have added is the communication between the data layer and the optical layer."

GATEWAY TO SDH Tellabs introduced the Titan 4500GS, a gateway that allows carriers to deliver global services between Sonet and SDH environments. It does not require data to be converted to an asynchronous format in the access network.

MILES AND MILES Bell Atlantic reached the 5 million-mile mark, having deployed that much fiber optic cable in its region, which includes 13 states and Washington, D.C. The carrier claims some 42 million telephone access lines in addition to 8.6 million wireless customers.