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Network World - Commercial VoIP service rollouts are taking longer than anticipated as early adopters of Session Initiation Protocol experience unexpected interoperability problems with the increasingly important communications mechanism.
SIP is the emerging standard for setting up telephone calls, multimedia conferencing, instant messaging and other types of real-time communications on the Internet. An array of network gear including IP phones, IP PBXs, servers, media gateways and softswitches support SIP.
The interoperability problems stem from vendors taking different approaches to SIP features such as device registration, user authentication and firewall traversal. The problems range from failed user logons that cause systems to crash to annoyances such as difficulty transferring calls.
Of particular concern to experts is that some vendors have not followed the SIP guidelines for failover when a server goes down. Companies that buy SIP servers without the correct failover mechanisms are more likely to experience service outages, experts say.
"This is the natural process of dealing with vendors that have not been compelled to interoperate with each other in the past," says Jon Peterson, a co-author of the SIP specification and one of the directors of the Internet Engineering Task Force's (IETF) Transport Area. "The avant-garde that deploys SIP is going to have to bear a little pain."
SIP proponents say such interoperability problems are common for a protocol of SIP's size, complexity and flexibility. The main SIP specification, which the IETF finalized in June 2002, is 260 pages. The IETF has issued an additional 22 documents that detail SIP features and extensions.
To help improve how SIP products work together, the SIP development community is hosting its 14th interoperability testing event, called SIPit, next week in Cannes, France. Sixty vendors are expected to send engineers to the SIPit event, which will include troubleshooting in such areas as device registration, user authentication and server failover. (The SIPit event is closed to the public and press, and no information is released about which products fail to comply with the standard. SIPit officials spoke to Network World about the most common interoperability problems.)
Until these problems are fixed, companies planning to deploy SIP should allow extra time for troubleshooting, particularly if they plan to roll out SIP's more advanced features, experts say.
"SIP is extremely flexible, but anytime you have [a protocol] that's flexible, you have different ways of interpreting things or doing things," says Ken Fischer, principal architect for softswitch services at Level 3 Communications.
Level 3 has deployed SIP with 30 service providers including Qwest and SBC since it announced a VoIP offering in September. The IP backbone provider says interoperability problems are adding an extra month of troubleshooting to each of its SIP deployments, which are taking twice as long as planned.
"The problems are all minor and annoying, but there's enough of them" to have business implications, Fischer says. "We haven't run into anything where we've said this will take six months to fix or we'll never fix this. But there are all kinds of things where we have to get three engineers into a room and work through code. . . . On the business side, if it adds four weeks to our schedule, then it's four more weeks between a sale and revenue."
Despite the delays, Level 3 remains committed to SIP and says it is the best technology on the horizon to bring multimedia communications to the Internet.
"The basic call control functions [of SIP] work pretty well out of the box, but that's not why SIP was invented. It was invented for the new services," Fischer says. "The good news is that people have wonderful ideas about new services. The bad news is that you have to work through interoperability problems with these new services."
Carriers such as Level 3 are experiencing the pain of SIP interoperability problems first because they are mixing and matching products from multiple vendors. However, the implications of the SIP interoperability problems could be serious for the dozens of companies such as IBM, Reuters and Monster.com that are rolling out SIP-based VoIP applications.
Reuters has run into all these interoperability problems in the past 18 months as it has deployed a SIP-based instant-messaging platform for the financial services industry that has 50,000 users each week. Reuters uses client and server software from Microsoft for its SIP applications.
"SIP is a session protocol, and it's very close to the application layer," says David Gurle, executive vice president for collaboration services at Reuters. "There's a perception that SIP will be as plug-and-play as TCP or [User Datagram Protocol] or IP or HTTP. But it's not going to be as easy as that because the higher you go in the networking stack, the more business logic you carry."
Gurle says Reuters has faced challenges getting its SIP-based application to integrate with non-SIP networks run by AOL and Microsoft, and SIP-based networks that IBM and others run. The hardest part of the process is translating between the business logic that these companies have built into their network applications.