IMA vendors fire up to fuse T-1s

Inverse multiplexing over asynchronous transfer mode has been enjoying a windfall lately. It seems as though each week brings a different vendor announcing IMA "standards-compliant" switching capabilities.

Part of the reason for the recent flurry of activity is the fact that the ATM Forum has frozen the IMA specification in its present state. IMA is expected to be approved at the next meeting when it comes up for a vote. With a standard in place, vendors' equipment should be able to interoperate and provide more choices for carriers.

However, incremental bandwidth demands are driving the IMA market.

Currently, end users can usually get T-1 (1.544 Mb/s) service or jump up to T-3 (45 Mb/s) service, provided it's even available in their area. Some carriers do offer fractional T-3 service, but it is usually expensive and difficult to provision. Between T-1 and T-3 lies a gap Dataquest analyst John Coons called "the sweet spot." Using IMA, companies can multiplex several T-1 lines using as little or much bandwidth as needed.

In addition to giving users fractional bandwidth options, IMA is expected to give T-1 sales a boost. As multiple services over one network become more popular, more bandwidth will be needed to run voice, video and data. IMA multiplexes several T-1 lines to make it seem like one large pipe that is able to carry more packets.

Aggregated traffic will quickly max out one T-1 line's capacity, even for a small site, Coons said. However, two or three T-1s would probably be enough--and the ideal configuration for IMA.

Theoretically, companies would only have to pay for as much bandwidth as they use at any given time. It remains to be seen exactly how service providers will tariff and charge for inverse multiplexed T-1s.

"If I were a carrier, what I would do is price T-1 ATM very competitively with T-1 frame relay so that it isn't an either/or situation," Coons said. "If ATM service is in the ballpark, a lot of folks might say, 'I don't know what I'm going to do in the future (with multimedia, for instance) and as long as ATM is about the same price, I'll take that.'" Siemens AG and Newbridge Networks, through their Public Communications Networks Group alliance arm, last week became the most recent vendors to say they will add IMA. The capability to multiplex up to eight T-1 lines on the jointly developed MainStreetXpress 36170 ATM switch will be generally available by fall.

"IMA is clearly going to be a nice, clear, flexible feature," said Ehab Shafik, Newbridge director of product marketing for ATM WAN. "It's one of the snazziest features that's been added to ATM switches in some time."

Service providers are looking for ways to offer fractional ATM services more easily, and IMA may be one way, said Rosemary Cochran, analyst with Vertical Systems Group in Dedham, Mass. Currently, only a few Bell regional holding companies and major interexchange carriers offer ATM T-1s, although several other RHCs plan to offer it by the end of the year. Tariffing, pricing and marketing of IMA are issues still to be discussed.

"The real message is it'll depend on how the technology gets turned into service features, capability and pricing," Cochran said.

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