The Protocol of Disagreement
Service providers and vendors draw battle lines over where and how the Internet meets the PSTN
By Peter Lambert. Peter Lambert is senior writer for tele.com. He can be reached over the Internet at plambert@cmp.com.
It's easy to believe that the path between Internet protocol (IP) and public switched telephone networks (PSTNs) has grown less tangled in recent months. The rash of mergers and cooperative efforts between voice network and Internet players certainly holds the promise that the gap may be closing. Unfortunately, appearances can be deceiving-especially when the pressing commercial interests of some providers are fostering a growing and increasingly ugly war of words between the two network camps over where and how datacom and telecom protocols should meet each other.
Consider the visceral initial reactions to the Internet Protocol Device Control (IPDC) interface specification. This proposed standard, released last month, would enable unified control of access "gateways" into both circuit- and packet-switched networks, allowing a common point of voice and IP traffic exchange. On the face of it, IPDC may seem noble enough, just one of several protocol proposals being considered by the Internet Engineering Task Force (IETF) working group on PSTN-to-Internet interworking and the International Telecommunications Union's (ITU) Study Group 11.
But IPDC isn't just any proposal-it's the solution of choice for well-financed fledgling carrier Level 3 Communications Inc. (Omaha, Neb.). Level 3's business existence will depend on its ability to smoothly hand off both voice and data traffic between incumbent circuit-switched PSTN networks and its own planned, all-packet-switched network, budgeted at $8 billion to $10 billion. It needs IPDC in place soon-perhaps before the slow-moving IETF can decide on any protocol proposal-if it is to meet its goal of offering service via leased network facilities by the first quarter of 1999.
Some of Level 3's competitors are concerned that IPDC, if adopted by the IETF, could threaten the Internet's open systems hierarchy. They're also not wild about how Level 3 and its 11 vendor partners went about developing and promoting it; to some, the whole effort smacks of putting one carrier's commercial interests above the general good of the market. "In my opinion, Level 3's public relations blitz is totally contrary to IETF history and process," says Henry Sinnreich, executive staffer, switched data architecture, for MCI Communications Corp. "It's technical excellence versus an onslaught of commercial self-interest."
Level 3 sees this all differently, claiming IPDC is fully interoperative with existing Internet standards while allowing for the easy addition of network ports. It certainly goes to the heart of Level 3's business plan, which includes a public vow never to deploy last-generation circuit switches. It backed up this commitment in April by spending $168 million to acquire XCOM Technologies Inc. (Cambridge, Mass.), a competitive local carrier that had developed software to manage that handoff. This software became a key part of the IPDC Internet-to-PSTN gateway-control interface that Level 3 developed through the ad hoc Technical Advisory Council (TAC), which includes 11 leading voice and data access equipment vendors.
All the proposed protocols under consideration have the same basic aims. They're designed to route data calls around overburdened PSTN voice switch gateways and onto Internet remote access concentrator (RAC) gateways; enable voice over IP (VoIP) services to travel freely between packet-switched and circuit-switched networks; and leverage the telephone carriers' mature Signaling System 7 (SS7) and advanced intelligent network (AIN) call control infrastructure to provide Internet data sessions with the enhanced services common to voice calls.
With IPDC, the unified control of both Internet and PSTN gateways would be supplied by a media gateway controller (MGC), which uses phone industry SS7 control signals to analyze incoming calls, then uses IPDC to instruct either a RAC gateway (to connect a data call) or a voice switch gateway (to connect a voice call). Level 3 plans to deploy nine MGC servers later this year to control up to 1 million ports in its own network. By integrating circuit and packet networks at the SS7 call control level, the IP network looks like just another circuit switch gateway to the controller, says Ike Elliott, Level 3's senior director of voice network engineering. In effect, IPDC moves call control management out of switches and RACs, and into a general purpose server. The separation of control and ports would enable rapid, flexible port growth without forcing storage and management of call control information on every switch and RAC, says Jennifer Pigg, senior vice president of datacom for The Yankee Group (Boston).
Through SS7, the MGC also would communicate with an AIN database to determine what enhanced services the caller is paying for-such as call forwarding, unified messaging, or authorized access to a virtual private network-then signal the appropriate media gateway to provide them.
A slew of IPDC-based products will begin surfacing by year's end through TAC vendor members, which include Cisco Systems Inc. (San Jose, Calif.) and Lucent Technologies Inc., among others. "A bridge has to be made, and we're trying to get as many workers on the bridge building project as possible," says Elliott.
Level 3 has also asked other service providers to sign up for IPDC. That support may not come as easily. An executive for another competitive carrier, who requested anonymity, says his company also needs a common packet-switched/circuit-switched gateway controller, but he notes that Level 3 invited in other carriers only after the spec was completed.
Beside this, IPDC simply may not be needed, Sinnreich says. IETF already has session initiation protocol (SIP), which he calls a well-established, universal method for controlling all networked machines, whether network gateways, PCs, or pagers. "We think telephony is a logical subset of multimedia," he says, "and we think we have the protocols already in the Internet that can be extended to interwork with ITU specifications like SS7, so you don't need separate protocols for a device called a gateway." MCI will back this up by pushing for SIP in the IETF this fall.
Elliott discounts these fears, claiming that IPDC can in fact interoperate with either the IETF's SIP or the ITU's H.323 session management protocols. "IPDC and SIP are two protocols that do different things and can work together," he says. Ultimately, that will be the IETF's call.
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