As a point-to-point private-line type service, Ethernet has not posed any great challenges for carriers with regard to the transport side of the equation. But that's about to change as more varied applications, greater numbers of customers and QoS distinctions bring the service into the mainstream.
One of the big issues the Bell companies face is whether to continue treating Ethernet as a dedicated fiber or, in the case of SBC, wavelength application or to begin folding it into the multi-service TDM stream over legacy SONET rings.
Whether SBC Communications Inc., for example, uses the new Multi-Service Optical Networking or legacy SONET capacity will depend on local market conditions as demand intensifies, says Ashley Blaker, a spokesman for SBC. The other carriers are equally vague at this point as to what steps they'll take to make more efficient use of SONET for Ethernet than is possible using the traditional TDM multiplexing approach, where a single gigE stream eats up an entire OC48 (2.5gbps) pipe. But there are some clues as to their thinking based on what they've deployed so far and what vendors are saying about the types of technology under consideration.
For example, ADVA Optical Networking Inc. is supplying BellSouth and Verizon with point-to-point FSP 500 access technology. ADVA's FSP 3000 metro DWDM solution, meanwhile, is in distribution with Sprint and Dominion Telecom as the first publicly named customers, each of which is deploying the version of the product marketed by Alcatel, known as the Alcatel 1690. Both ADVA products are designed to transport virtually any type of telecom service either in native format or in SONET TDM mode, (see diagram below) says Abdul Kasim, vice president of marketing for ADVA.
ADVA'S Optical Networking Solution Chart
Source: ADVA (www.san.com/advice)
If a carrier wants to map gigE into SONET as opposed to assigning it a wavelength over the metro system, the ADVA platform strips redundant information from the Ethernet packet headers, thereby making more efficient use of the bandwidth, he adds.
Finding a way to use SONET in the migration to gigE is vital at a moment of reduced capital spending and intensifying competition in this space, notes Colm O'Brien, director of product line management and co-founder of startup Mahi Networks Inc. Mahi plans to begin supplying its core metro next generation Optical Transport Switch Router for trials slated this summer with a number of RBOCs and IXCs. The platform is designed to handle traditional SONET cross-connect and packet switching over a single processing fabric. The system also supports use of statistical multiplexing to accommodate efficient transport of gigE over SONET, allowing carriers to continue selling gigE as leased line point-to-point service in the manner and at prices customers are accustomed to paying while avoiding stress on transport capacity.
Another vendor moving to trials this year with RBOCs interested in Ethernet-over-SONET is Coriolis Networks Inc. "We've negotiated lab schedules with three of the four RBOCs to take place in the first quarter and hope to move to field trials by the second half of the year," says Greg Wortman, vice president of corporate marketing at Coriolis.
The Coriolis OptiFlow system provides a means for managing bandwidth dynamically across all nodes of a SONET ring. This is done through a combination of optical service units at customer premises that break down the native protocol into TDM segments of 576kpbs per second. A master controller trunk unit, meanwhile, multiplexes all the bit flows coming in from the service units onto OC48 pipes. The software management system looks at all nodes and is able to shift bandwidth allocation as the add/drop flow at each node fluctuates, without regard to which type of protocol is being added or dropped, Wortman says.
Notwithstanding such compelling new solutions, it remains to be seen how quickly the RBOCs will make use of them. BellSouth, for example, has ample SONET capacity to accommodate Ethernet traffic without adding new technology, Kaish says. It might have enough capacity to wait until it can skip to the next-generation DWDM model, much as SBC is doing with its MON architecture. "Some of this stuff (like Ethernet over SONET) is technology in search of a problem," Kaish says. "Maybe we simply use what we have and skip a generation and go directly to the optical family of solutions when the time is right."
But all the Bells are looking at the interim options, BellSouth included. More than likely, some -- at least in some markets -- will find that the escalating demand for Ethernet leaves them no choice but to make more efficient use of their legacy networks. "It's not a very compelling service when you use up 155 megabits in an OC3 pipe to deliver Fast Ethernet (100mbps) to one customer," Wortman says.
"We don't have an Ethernet access offering at this point, but we're building toward that type of service."
