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Salira details its EPON technology

By Marguerite Reardon
Network World Optical Newsletter, 02/18/02

Salira Optical Network Systems, a start-up developing gear for Ethernet passive optical networks, recently announced details of its architecture.

Passive optical network (PON) technology is an access technology that splits the use of fiber with passive couplers in order to share the bandwidth across multiple end users, such as residential customers or businesses. Recently, interest has grown in PON development, because it is significantly less expensive than equipment that uses active components like lasers.

While the earlier players in the market have focused on ATM-based PONs (APON), newer start-ups like Salira and Alloptic argue that EPONs are ultimately more cost-effective than their ATM cousins. Some experts agree.

" When they're more widely deployed, EPONs should be cheaper than APONs, " says Michael Howard, principal analyst and cofounder of Infonetics Research. " The interfaces will likely be cheaper, and packet-based networks are cheaper to operate than circuit-based networks. But it's hard to say which technology will win. The market is still so young. "

For some vendors, the ATM vs. Ethernet debate isn't that simple. For example, Quantum Bridge, which already has an APON product, recently announced support for Gigabit Ethernet interfaces.

While Salira's approach is based on Ethernet, company executives emphasize that its architecture supports the transport of all legacy time-division multiplexed (TDM) traffic, including frame relay and ATM. This allows service providers to migrate their networks from legacy TDM services to packet-based services.

" Support for legacy traffic is important," says Howard. "[regional Bell operating companies], [interexchange carriers], [incumbent local exchange carriers] - they all have a lot of TDM traffic in their networks. And they don't want to throw that out. "

And unlike other platforms that may support these traffic types through frame encapsulation, cell or packet conversion, or circuit emulation, Salira will support these TDM traffic types in their native mode. Tom Walsh, vice president of marketing and sales for the company, explains that the distributed network intelligence layer is designed to recognize the type of TDM traffic coming in on a T-1/E-1. Then a T-1/E-1 worth of bandwidth (1.544M/2.048M bit/sec) is carved out of the 1.25G bit/sec PON circuit and reserved for native-mode TDM transport.

" Effectively, we have created a T-1/E-1 over fiber instead of copper, " he says. " All T-1/E-1 traffic is groomed by type [such as ATM integrated access device (IAD), frame relay, ATM, voice, ISDN PRI and so on] and loaded on the appropriate network interface [such as DS3, E-3, STM1 or OC-3]. "

Walsh says keeping the TDM traffic in its native format ensures that the timing signals of the traffic aren't disrupted. This also allows the operational support mechanisms already in place to continue working.

Walsh claims that Salira's architecture offers a high level of quality of service, which will allow service providers to create detailed service-level agreements. The product will also allow dynamic allocation of bandwidth and remote creation and management of services.

While it's true the EPON market and the PON market in general are in their early days, Salira is far from the first arrival. Alcatel, Marconi, NEC and Quantum Bridge - APON vendors all - are in multiple trials. EPON vendors like Alloptic, OnePath Networks and Wave7 Optics are all supposedly in trials with their products. For its part, Salira isn't expected to have products in customer labs until the end of the second quarter of this year.

But Salira's timing may be right - with carriers like Qwest, British Telecom and Deutsche Telekom evaluating new access technologies. Some carriers, like Verizon, say they will continue to spend money on next-generation equipment, but they are also cautiously evaluating new technologies as they wait (and lobby) for Congress and the Federal Communications Commission to iron out issues in the last mile.

Marguerite Reardon is a senior editor of Light Reading (www.lightreading.com), an optical networking Web site. She can be reached at reardon@lightreading.com