IETF addresses SIP interoperability


Session initiation protocol (SIP) is a text-based Internet protocol, similar to HTTP and SMTP, for interactive communication sessions between users. It is used to establish, maintain, and tear down Internet sessions of any kind-gaming, video, chat, plain voice, and virtual reality. Following the debut of SIP in 1997, the Internet Engineering Task Force (IETF) issued Proposed Standard RFC 2543 in 1999. SIP is now evolving into an important signaling protocol for Internet telephony.

The first step in the IETF standardization process is the designation of a "proposed Standard" (see Lightwave, September 2000, p. 30). Specifications generally go through various phases called Internet Drafts, (I-Ds) before being accorded Request for Comment (RFC) status. SIP, as embodied in RFC 2543, is a Proposed Standard. Through operational experience, a Proposed Standard can evolve into a Draft Standard and eventually to the last rung, an Internet Standard.

To provide SIP interoperability and advance the standardization of SIP, three times a year the IETF holds SIP Interoperability Test Events (a designation that has replaced the term "bakeoffs"). At an SIP Test Event, vendors bring their implementations that have been coded based on the RFC. Vendors are encouraged to interoperate their implementation with as many others as they can. All feedback thus gained is forwarded to the Test Event Committee, which feeds it to the RFC authors for inclusion in the RFC (typically, the Test Event Committee consists of the RFC authors, as well).

So far, there have been seven SIP Test Events. About eight companies participated in the first such event in April 1999. By the fourth Test Event in April 2000, participation had increased to 35 companies and 150 developers. In recent SIP Test Events, organizers have had to impose a cutoff limit of 200 attendees to maintain some semblance of order.

The focus of the Test Events has shifted over time from basic call setup to more complicated service scenarios and ensuring robust operations with network and server failure. Information on the Test Events is available at the Website,

Vijay Gurbani works for the Internet Software and eServices group at Lucent Technologies. He has represented Lucent in four of the last seven SIP Test Events. Vijay can be contacted at tel: 630-224-0216; fax: 630-713-0184; e-mail:

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