High-speed rings are here: Bandwidth-hungry carriers count on BLSR to bring OC-192 to the fore

Northern Telecom and Hitachi Telecom are throwing a coming out party for OC-192 rings. This month, Hitachi began shipping four-fiber bidirectional line switched ring technology for OC-192, and Nortel is announcing this week its four-fiber BLSR offering for OC-192.

Considered a natural evolution for OC-192 (9.6 Gb/s), four-fiber BLSR brings carrier-coveted ring survivability to high-speed networks. The new survivability feature will make OC-192 migration a no-brainer, said Steve Carter, senior manager of account marketing at Hitachi Telecom.

"Now with four-fiber BLSR, you can have your cake and eat it, too," he said. "You can have higher bandwidth with OC-192 without compromising your ring topology."

Brian McFadden, vice president and general manager of optical network applications at Nortel, noted that most carriers have planned for a transition to OC-192 and will deploy wavelength division multiplexing (WDM) to further boost capacity.

In addition to ring survivability, the four-fiber ring also provides high capacity capabilities and flexible capabilities, he said. "It's not how much capacity you put on the fiber, but the total network capacity. OC-192 rings give you much more capacity, and when combined with our 32 [channel] WDM, we can get 320 Gb/s on a fiber in a ring configuration." It lets carriers provide OC-48c (2.4 Gb/s) services-concatenated service on a completely protected, survivable ring, he said.

Most current OC-192 environments are typically used in long-haul or point-to-point applications. OC-192 allows carriers to deploy services more quickly, but without BLSR, the network lacks true ring reliability. Still, this is sufficient for some carriers, which claim the absence of a ring topology is insignificant because other checks inherent in the system keep errors at a minimum.

"In a linear system, OC-192 makes a lot more sense because you can turn up service quickly," explained Carter. "All of the new interexchange carriers are building OC-192 linear systems because they are trying to get the network up." But because they don't have a ring, they can't do fiber restoration, he said. "It is just now becoming available, and they are overlaying or upgrading existing point-to-point networks with a ring network."

Carriers that deployed OC-192 in a point-to-point fashion were willing to take the risk and upgrade later. "It can be bad for the customer," Carter acknowledged. "There are other ways of making the network survivable, but they are not nearly as robust as all rings."

Why build a network that you have to upgrade in six or 12 months? "It's a question of economics," Carter said. "For many carriers, getting the service up and getting customers to buy into that service is more important than guaranteeing the robustness of that service. The demand for bandwidth far outweighs the demand for a survivable network."

Some carriers such as Frontier Corp. resisted the OC-192 temptation until ring survivability was available. They simply deployed four-fiber BLSR in their OC-48 networks. Now their patience has been rewarded.

"Now OC-192 is available in a ring. It has caught up feature-wise with OC-48," said Carter.

It was worth the wait, said Jim Watts, director of network development at Frontier. The carrier uses NEC's 16-channel WDM system, an open architecture that put off the immediate need for OC-192.

"We are more concerned with survivability," Watts said. "That's why we elected to go with four-fiber BSLR ring design in the [OC-48] network-so we have the protection."

Carter predicted that nearly all long-haul carriers will migrate from OC-48 to OC-192 in 1999. The metro environment will turn to OC-48, he said. He also argued that OC-192 in a metro environment can make economic sense (see sidebar).

Not everyone agrees that OC-192 rings will usurp OC-48 with BLSR immediately. It's not a proven solution, critics claim. Although four-fiber BLSR implementations are standards-based, vendors choose differing methods for ring node communication, WDM support and signal grooming, said Rich Moran, director of product marketing in the business development division of NEC's public networks group. Dense WDM adds another twist because four-fiber BLSR protects the physical fibers but not the channels within the fiber.

"OC-192 is just beginning to be introduced now," pointed out Steve Cortez, manager of product marketing in the transport product management division of NEC's public networks group. "There is no standard for that type of an upgrade. When you overlay OC-192 on OC-48, you still have to meet the span distances and span topology architecture. Then you have to meet the interlocking grids. You have to be able to have the standard between different rates."

Moran offered a note of caution to carriers looking to migrate to OC-192: "If you are moving to a 10 Gb/s speed, the fiber may not be able to work as well at the higher speeds. Frontier, Sprint, AT&T-they chose DWDM with OC-48 rather than OC-192."

Nortel's McFadden is more optimistic. "My view is the capacity requirement is not going to slow down," he said. "Stop planning for OC-192 implementations and start putting them in today. [OC-192 with four-fiber BLSR] is higher capacity and enables protective service at a level OC-48c cannot."

DSL IN DEUTSCHLAND Deutsche Telekom is rolling out DSL with a vengeance. The carrier is buying Orckit Communications' FastInternet ATM ASDL system and ECI Telecom's ADSL-based Hi-FOCuS Broadband Access to the Home solution. The two suppliers will bring service to about 58,000 lines, a majority of the 70,000 lines Deutsche Telekom plans to deploy.

MULTIYEAR CONTRACT CALLS FOR SWITCHES Ascend Communications signed a contract extending its relationship with Bell Atlantic. Ascend is outfitting Bell Atlantic with its ATM and frame relay multiservice and core switches and Navis network management software.

THE APEX OF A PAN-EURO NETWORK General DataComm is providing its Apex ATM equipment in cooperation with Lucent Technologies to Unisource Carrier Services, a European wholesaler of voice traffic. The switches will consolidate voice, data and Internet services over an ATM network across Europe.

If you think OC-48 in a metro ring sounds like overkill, sit down. Steve Carter, senior manager of account marketing at Hitachi Telecom, is suggesting OC-192 for metro environments.

"OC-192 is debatable on whether it makes sense in metro environments," Carter said. Competitive local exchange carriers "are starting to realize that in metro rings, it makes more sense to build high-capacity OC-192 rings than to build lower-speed metro rings."

Most consider an OC-192 equivalent to four OC-48s, but in terms of performance, that measure is inaccurate,Carter said The ability to pass traffic between rings with OC-192 buys more bandwidth on the line. According Carter, one four-fiber bidirectional line switched ring OC-192 line can be equivalent to 11 OC-48 lines. And his researching concluded that OC-192 costs 15% less.

Carter modeled a five-node metro ring less than 50 miles in length. First he modeled it using OC-48 two-fiber BLSR with a metro-optimized dense wavelength division multiplexing system. Then he tried OC-192 four-fiber BLSR with subtending OC-48s. Taking both networks through 12 growth stages, the traffic ran over 276 DS-3s, five OC-12s and three OC-48s.

The results will be presented this week at NFOEC, but here is the crux of Carter's argument: Continuing to add OC-48s gets expensive in terms of equipment such as cross-connects and lost bandwidth. It's better to fork over the cash for OC-192 upfront because the equipment savings and more efficient line grooming will pay off in spades.

"Most people don't even think of OC-192 for a metro application, but it proves in quite well, " Carter said. "OC-192 in a metro application is more economical for deployment of DS-3s than OC-48. In an OC-192 network, the grooming at the OC-192 level is more efficient than an OC-48 multiwavelength network."

DWDM will push off the need for OC-192 metro rings, he said, but Carter stands by his numbers. "The grooming ability in OC-192 allows you to take the efficiency further than you think. Four is the economic break point, but 11 is the performance break point," he said.

Jim Watts, director of network development at Frontier Corp., was skeptical. "I really want to see him do that," he said. "There are definite benefits [of using OC-192 in a metro environment], but 11-to-1 is a stretch."