IP telephony talk zeroes in on SIP

SEATTLE - As voice over IP gains momentum in large organizations, experts say forward-thinking network executives should familiarize themselves with three letters: S, I and P.

Session Initiation Protocol was on the minds of customers, analysts and the vendors who were pushing a lineup of new SIP-related products at the Voice on the Net show last week.

SIP is an Internet Engineering Task Force protocol, similar in format to HTTP, used in applications to establish and terminate communication sessions over IP (see "The Scoop"). SIP applications include voice conversations, instant-message-style text chat and video. The technology is considered by some to be the successor to H.323, which is used as the base of a majority of IP voice products. One of SIP's draws is the promise of voice-over-IP (VoIP) interoperability among IP PBX, phone and gateway products, something lacking in current IP telephony systems.

SIP is being considered as a possible foundation for a voice network at Boeing, according to Michael McInnis, a network engineer at the Seattle aviation company.

"We're looking to migrate to voice over IP on a companywide basis," says McInnis, who attended Voice on the Net. "Some things I've seen here that can be done with SIP - like being able to organize a conference call through a [Microsoft] Outlook directory - sound pretty advanced - things I didn't even know could be done."

Boeing's voice network is built on five carrier-scale, time division multiplexing-based Lucent 5ESS voice switches, which support a user base of 185,000 employees. The company also has pockets of IP voice installed, with Cisco's CallManager IP PBX and about 2,000 phones deployed around the country. CallManager supports Cisco's Skinny Client Control Protocol and H.323, which will only go so far at Boeing, McInnis says.

"H.323 is not scalable enough to fit our needs, and it's also not as [voice and video convergent] as perhaps SIP is," he says. "We want to merge video with VoIP and we can't do that very well today on H.323."

The other factor that makes SIP appealing to McInnis is interoperability. "We're locked into the kinds of phones we can use with the Cisco [VoIP] product," McInnis says. "We want to get away from proprietary protocols and get into a more distributed model for telephony."

Although some call SIP the communications technology of the future, detractors say it will always be just that - an oft-talked-about but rarely deployed technology. A majority of enterprise VoIP gear is based on H.323 or Media Gateway Control Protocol, and SIP's installed base is relatively small compared with other VoIP protocols. Issues also remain with SIP, such as how to make it secure and interoperable with firewall and network address translation technology (NAT).

"I don't know of a huge amount of activity with SIP in the enterprise at this point," says Tom Valovic, an analyst with IDC. "Most [IP PBXs] deployed in enterprises are H.323-oriented. I don't really think SIP is playing large role with the exception of maybe a very large enterprise."

An IP voice system based on H.323 from Avaya is being installed at The Seattle Times.

"SIP is something we've been hearing about, and reading about," says Thomas Dunkerley, the newspaper's communications manager. However, his department is busy enough just getting IP voice off the ground, he adds. "SIP is something that probably won't affect us for a while."

At Avaya, product planners say they are ready to put SIP in the enterprise now, but will hold off on releasing SIP enterprise gear until users like Dunkerley start clamoring for it.

"We have [IP phones] that are SIP-capable," says Venkatesh Krishnaswamy, a VoIP product director with Avaya. "SIP has been tested on our enterprise IP telephony gear and is ready for the enterprise today, [but] we just aren't seeing a demand for it."

Nevertheless, VoIP equipment and services vendors were anxious to push their SIP-related product announcements at Voice on the Net.

Ingate introduced a firewall that the company says addresses a glaring security problem with SIP.

"You can't run SIP over most industry-standard firewalls," or between sites using NATs, says Steve Johnson, an Ingate vice president. The Ingate Firewall is a $2,500 box that would sit at the edge of a WAN or Internet connection and provide firewall traffic filtering with support for SIP VoIP traffic. According to the company, the box supports SIP on dynamically allocated ports on the firewall, which can allow businesses to pass large volumes of calls through the box, as opposed to opening a specific port on a firewall for VoIP, which could leave a network open to intrusion.

Aravox and Cisco also have firewall products that can support VoIP and SIP.

Conferencing server vendor eDial demonstrated SIP-based features with an application that integrates voice and e-mail by allowing end users to start a conference call by clicking the names of conference participants in a Outlook directory. The eDial server then rings the participants' phones to join the call.

Microsoft demonstrated the combined IP voice, video and instant-messaging features of the SIP-based Windows Messenger application, released last fall as part of Windows XP.

"As of January, there were 17 million Windows XP clients out there ready to start using [voice over IP] minutes," says Jawad Khaki, a Microsoft vice president. "The value of SIP to the enterprise in terms of new applications and enhanced productivity are more than enough to justify the infrastructure changes that will be necessary to support it."

Polycom and Pingtel were among IP vendors announcing hardware and software IP phones at the show.

Polycom is adding SIP to its SoundPoint 500 IP phone and Soundstation 3000 IP conference station. Pingtel introduced a software version of its IP phone that runs as a Windows desktop application and requires a standard headset accessory.