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SIP Packs a Punch: Page 3 of 9

Why? SIP is more extensible, simpler to implement and easier to troubleshoot thanks to its simplicity and text-based messages. The SIP protocol requires fewer packets to be exchanged to set up a call, which means less network traffic, less work for the servers involved and thus greater scalability. SIP is also more flexible than H.323. There's a whole industry developing based upon SIP products. Take a look at www.sipcenter.com for a sampling of some of the equipment and application vendors. A standard like this provides a much larger market for developers than proprietary products can provide, which in turn increases competition and innovation.

Many feel that H.323 is still superior for managing video services. But this hasn't stopped companies like Wave Three, VCON Visual Communications and others from providing SIP-based video products. And some IP vendors with legitimate interests in standards-based connectivity adapted H.323 for their phones before SIP was a viable standard.

There's further evidence of SIP's knockout power on the server side: Microsoft's new RTC (Real Time Communications) server will use SIP for all of its media-related communications. The first application that Microsoft will introduce on this platform will be a corporate messaging product. The company also plans to provide RTC as a development platform. Siemens, for example, will incorporate RTC in its future products to enable it to standardize its messaging and presence applications.

The bottom line, though, is that the industry has declared SIP the winner.

We know what you're thinking: Microsoft appears to have embraced SIP with enthusiasm, but given its track record with standards, how long will the true spirit of interoperability survive? Along with our review of SIP phones (see "Polycom KOs Proprietary VoIP Woes,"), we did some testing with MSN Messenger and XP Messenger, and found that there is indeed a lot of interoperability at the client level. For example, we used BroadSoft's Proxy and Registration servers to set up voice and video sessions between Microsoft clients (see "The BroadSoft Connection"). Taking it a step further, we established voice conversations between all of our SIP phones and Windows clients.

Microsoft's client implementation of SIP is not perfect, however: Whenever we called XP Messenger with a SIP phone, the local XP Messenger client responded by displaying a message that the calling device wanted to establish a "voice and video conversation," even though the phone had no video capability. This happened with every SIP phone, even when attempting to establish a voice-only call from version 4.6 of MSN Messenger, which has no video capabilities! This was disappointing because one of the strengths of SIP is that it can use SDP to negotiate media capabilities between devices. The Microsoft client obviously wasn't designed to take advantage of this design. Microsoft had no response to our queries about this problem.