MINNEAPOLIS - The Internet Engineering Task Force (IETF) is working on specifications that will ensure IP networks of the future will be able to handle voice calls as reliably as today's public switched telephone network (PSTN).
At last week's Minneapolis meeting, IETF members debated whether to preserve the PSTN's native signaling protocols, including SS7, or create new IP control protocols.
Specifically, the Signal Transport Working Group struggled with how to send SS7 signals over IP networks, while the Media Gateway Control Work-ing Group heard arguments for a new protocol that could let media devices, such as PBXs, interact without PSTN signaling. SS7 is a switch-to-switch protocol that lets telephone switches set up calls, manage circuits and perform intelligent network functions.
Cisco and other router vendors would have customers believe that widespread voice-over-IP service is just around the corner. But telco equipment makers, such as Nortel Networks, are quick to point out that every company has a long row to hoe to get to that point. Therefore, interim standards are needed for IP networks and the PSTN to communicate with each other.
The IETF's Signal Transport Working Group is developing a standard that will let IP switches or gateways understand SS7.
The Signal Transport Work-ing Group is developing protocols that will let two switches that are transporting voice traffic over an IP network communicate, says Scott Bradner, transport area director for the IETF. "It's a way to replace the wires in the phone network with IP connectivity," he says. In the long run, this is the IETF's goal.
"Some people would like to see SS7 go on forever," says Fred Baker, IETF chair and Cisco engineer: "That's very unlikely."
The IETF's Media Gateway Control Working Group is operating under the assumption that SS7 networks will morph into pure IP. The pending media gateway control protocol defines how media devices should control packets.
The media gateway control protocol, for which two drafts were presented at the meeting, will determine how calls are manipulated and forwarded. For instance, if a company is supporting voice over its extranet, those calls would pass through a gateway that supports the media gateway control protocol.
The protocol gives the device the ability to determine if a call should be sent over the company's intranet, over the Internet or over the PSTN. The working group will define its own signaling protocol specific to IP.
Both working groups say their specifications will be ready by year-end, but multinetwork interoperability is still 18 to 24 months off, says Krishna Sai, a network software engineer at IETF member ECI Telecom in Jacksonville, Fla.
Service providers are not only depending on the IETF for voice-over-IP standards; they are looking to the International Telecommunication Union and vendor driven forums such as iNow to address billing and voice traffic exchange specifications that promise interoperability.
PSINet, one of only a few ISPs offering a business-oriented voice-over-IP service, is looking for interoperable settlement systems so multiple carriers can handle voice traffic.
Today, PSINet only offers its customers an intranet, PBX-to-PBX voice-over-IP service: The ISP says it's the only service that can be supported with strong service guarantees. As technology and standards develop, PSINet plans to expand its PSIVoice service offerings.
