SIP passes taste test

The Session Initiation Protocol is winning converts among the voice-over-IP crowd.

The Session Initiation Protocol has gained industry momentum for its promise as the future of real-time voice, video and messaging applications. But early adopters like it for one reason - it's very simple to manage.

SIP is an IETF standard for establishing and terminating real-time application sessions over the Internet. SIP's creators built it similar to HTTP, the standard for transmitting Web page information. SIP is text-based, meaning that commands are coded in a format that makes it easy for application developers to write programs that use it.

The protocol operates at Layer 7 of the Open Systems Interconnection model stack, in conjunction with TCP/IP and Real-Time Protocol (RTP), which are Layer 3 and Layer 4 protocols. TCP/IP and RTP transmit packetized voice and video in sessions established with SIP.

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Click to see: Early Adopters

SIP is an IETF standard for establishing and terminating real-time application sessions over the Internet. SIP's creators built it similar to HTTP, the standard for transmitting Web page information. SIP is text-based, meaning that commands are coded in a format that makes it easy for application developers to write programs that use it.

The protocol operates at Layer 7 of the Open Systems Interconnection model stack, in conjunction with TCP/IP and Real-Time Protocol (RTP), which are Layer 3 and Layer 4 protocols. TCP/IP and RTP transmit packetized voice and video in sessions established with SIP.

"We're interested in SIP as the key component to a base voice-over-IP architecture," says John Kristoff, research and design manager for the networks and telecom group at DePaul University in Chicago. The school recently installed a test SIP deployment with 15 SIP phones from Pingtel, along with Pingtel's Linux-based SIPxchange IP PBX.

"VoIP and SIP are really separate, and one does not necessarily rely on the other," Kristoff says. "However, SIP is the preferable core architecture for implementing VoIP."

Kristoff says the simplicity of the protocol, along the lines of TCP/IP, allows it to be deployed on networks without requiring lots of technical rejiggering of network equipment or protocols. Basically, if a network can support Web traffic, it can run SIP.

VoIP vendors such as Siemens, Nortel, Alcatel and Cisco have made plans to come out with SIP-based VoIP servers by year-end or next year. For smaller deployments, Mitel and Pingtel offer SIP-based phones and IP PBX products.

Last year, SIP got a shot in the arm when Microsoft threw its weight behind the protocol by including it as the base call set-up technology for its Windows Messenger application in Windows XP. The successor to Microsoft's H.323-based NetMeeting, Windows Messenger integrates voice, video, instant messaging and "presence management," an instant-messaging feature that notifies users who on their buddy lists is available.

Sometimes, the best technologies are the ones you don't even notice are there. This is the case at Computer Korner, a PC retailer in Ottawa. The business has two stores in the city, and recently installed Mitel's SIP-based 3050 IP PBX and 5505 IP SIP phones to support the locations.

"What we had previously wasn't a system; it was just some Bell [Canada] lines. We were looking for a system for a way to better utilize those lines," says Dave Hill, Computer Korner owner, who worked with Mitel engineers to install the box.

The 3050 is an all-in-one small-office PBX, and also includes a firewall, file-and-print server and router.

The telephony part of the device is based on SIP, which lets boxes deployed across a wide area find each other easily and interconnect with minimal configuration.