A switch or a mux? Access system aims to ease DSL deployment

Taking a new tack to implementing digital subscriber line services, upstart Promatory Communications introduced the Intelligent Multiservice Access System, combining the functionality of a DSL access multiplexer with an asynchronous transfer mode switch.

"The IMAS is central office equipment, but it's not a DSLAM. It's a broadband access device," said Tim Waters, vice president of marketing.

DSLAMs provide aggregation, but they support only one flavor of DSL. The IMAS incorporates full ATM traffic management and quality of service features, and it supports asymmetrical DSL, ISDN DSL, symmetrical DSL, G.Lite high bit-rate DSL, very high bit-rate DSL, as well as T-1 (1.54 Mb/s), DS-3 (44.7 Mb/s) and OC-3 (155.5 Mb/s) interfaces. In a three-shelf SDSL configuration, the IMAS supports 1700 users, with up to 576 users per shelf. The Java-based network management system can be accessed from any browser.

In a traditional DSLAM environment, the system must provision a permanent virtual circuit between the DSL modem to the DSLAM and to the ATM switch. Each switch-to-switch link also requires PVC provisioning. IMAS uses Promatory's Proxy-SVC technology, which creates a switched virtual circuit to the router (see figure).

"You don't have to provision four or five PVCs for each user. The PVC comes into our device, and we translate that to an SVC to communicate with the ATM network," Waters said. That will minimize operating costs because carriers only need to provision a PVC from the user to the IMAS, he added.

Promatory also brought to fruition the idea of hot-swappable software modules. Carriers can upload software while the system is running. It operates on a "snapshot" of the system until the new software is installed and the system has successfully cut over to it. The process is transparent to users.

Further emphasizing the difference between the IMAS and a DSLAM, Tom Mitchell, director of product management, said, "you can't internetwork DSLAMs. We're an ATM switch, so we have all the networking capabilities, and we can aggregate more users on multiple DS-3 or OC-3 uplinks."

Positioning the DSL-oriented IMAS as an ATM switch is unique, said Christin Flynn, a data communications analyst with The Yankee Group. "There are not too many other ATM switches out there with this breadth of DSL options." The backplane is "fairly sizable for an ATM switch going into the central office but focusing on the DSL portion of things," she noted.

The Yankee Group estimates that the number of DSL subscribers will reach 1.4 million by 2002, said Flynn. "That's a substantial market, and there are definite possibilities there. But I don't know if the best way to market it is as an ATM switch."

Clearly a market for DSL exists, and the IMAS "will accelerate DSL deployment," Waters said.

But the success of DSL is complicated by regulatory issues, said Tom Nolle, president of Cimi Corp. Regional Bell operating companies have little incentive to deploy DSL because they have to sell it to competitive carriers at cost, he said. RBOCs can deploy DSL out of a separate subsidiary and competitive local exchange carriers can co-locate equipment in the RBOC CO, but the equipment can't provide voice services.

Although the IMAS can operate with voice services, Promatory ships it with that capability disabled, Waters said.

The added functionality will position the IMAS "not as an access device but as a device on the edge of the [time division multiplexing] network," Nolle said. "Putting ATM features into a DSLAM adds to the value of a DSLAM."

The competitive price point will help, he added. A 19-inch IMAS system fully configured with SDSL costs $388 per port.

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