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SIPit 15 Advances SIP Interoperability for Multimedia Applications

Wide range of “bugs,” interoperability issues addressed at leading test event for important voice-over-IP standard.

TAIPEI, Taiwan, and STOCKHOLM, Sweden (September 8, 2004) – The recent 15th SIPit ( interoperability event, the leading test and development sessions for the voice-over-IP community worldwide, further advanced the Session Initiation Protocol (SIP) standard, addressing a wide range of small performance issues and pushing the envelope on mixing multiple media in IP communications.

SIPits are organized by the SIP Forum (, the international organization for the development and promotion of SIP. The event, which took place in Taipei Aug. 23-27, was hosted by the CCL-ITRI (Computer & Communications Research Laboratories, Industrial Technology Research Institute,, a government research and development organization in Taiwan.

Even a typhoon hitting Taipei during the test event did not dampen the enthusiasm or slow the progress of the more than 70 companies attending the SIPit, thanks to the careful preparation and management of the session’s hosts. Nearly a quarter of the attendees were first-time participants in SIPits, which demonstrated that holding the event in Asia enabled many companies from that region to join the SIP interoperability effort.

Fixing “Bugs” and Expanding SIP

The 15th SIPit demonstrated again the overall soundness of the SIP protocol, as most participants, even those that had never attended a SIP before, had little difficulty establishing communication and making features work, such as hold or transfer. “They passed the core functionality tests very quickly,” says Robert Sparks, newly named chief technology officer of soft phone maker Xten Networks Inc., and coordinator of the SIPit events. “Very few people were having to argue with basic call and transfer.”

The challenges addressed by the sessions involved pushing SIP into new territory, ironing out interoperability issues with the use of multiple media audio, video, instant messaging within SIP sessions. The majority of SIP end points (telephones, soft phones) today still function mostly just as phones.

However, now companies are developing more products that mix audio and video, and also may include instant messaging, email, voice mail, application sharing and even redundant audio in a different language. The issue is how to make sure that receiving devices know exactly what media streams are being sent and their characteristics. “Once we get beyond sending just one audio stream, there are folks having issues with interoperability,” Sparks notes.

While there was significant progress in identifying and resolving those issues, multiple media has become a priority for the test sessions. “So for next SIPit, we will have a lot of test scenarios for that,” says Sparks.

Torture Tests

The sessions also included a kind of torture test for consultative hold and transfer, in which a recipient is first notified that a call is about to be transferred to them, and then the call is transferred. In the torture test, all the participants signed on to the test network and a consultative hold and transfer was made among all of them, one after the other.

The torture test used a new addition to the SIP standard, called GRUU (globally routable user agent universal resource indicator). While the earlier mechanism for doing this had been somewhat “fragile,” says Sparks, the new method “solves problems and tends to transfer nicely. And if you abort the transfer, it solves how to get the call to the right place.”

The SIPit sessions provide expert assistance from some of the most experienced SIP engineers in the world. “Having these people on hand means participants can test quickly rather than spending time setting up,” says Sparks. “Participants say they get weeks of testing out of the few days that they are there.”

The next SIPit, the 16th SIPit, will be held in March in Banff, Alb., Canada, hosted by Jasomi Networks (

About the SIPit Events

SIPITs, or Session Initiation Protocol Interoperability Tests, are week-long events where companies bring their SIP implementations to ensure they work together. The SIPITs are open to anyone with a working SIP implementation. Currently, the SIPITs are held twice a year. Different companies or organizations host each event, and each host chooses the venue. The goal of the events is to refine both the protocol and its implementations. The SIPITs are a driving force shaping SIP into a globally interoperable protocol for real time Internet communication services. For more information about the SIPit events, visit

About the SIP Forum

The SIP Forum’s mission is to advance the adoption of products and services based on the Session Initiation Protocol (SIP). The forum provides information on the benefits and capabilities of SIP, highlights successful applications and deployments, and directs activities aimed at achieving high levels of product interoperability. The forum promotes SIP as the technology choice for multimedia, real-time communication session control throughout the Internet, corporate networks and within next-generation wireless networks.

About SIP

SIP was developed by the IETF (Internet Engineering Task Force), the international organization responsible for all the basic Web protocols, such as HTTP and the mail protocol SMTP. It is part of the newest generation of communication protocols, those that tie together the telecom and Internet worlds. SIP offers many advantages to telecom vendors and service providers, including rapid development of products and services, lower costs up front and ongoing, and a wide choice of compatible vendors and products.


Larry Schessel
Cisco Systems Inc.
for the SIP Forum

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