Microsoft NetMeeting has developed a substantial following over the past few years, but as Microsoft developed Windows XP, the company recognized the need for an improved conferencing platform that would enhance the user experience and be able to interact with new third-generation wireless products. But unlike NetMeeting, which is based on the International Telecommunication Union (ITU) H.323 telephony and videoconferencing standard, XP's Windows Messenger uses the Internet Engineering Task Force (IETF) Session Initiation Protocol (SIP). Because the two protocols use different session setup mechanisms, videoconferencing between NetMeeting and Windows Messenger is impossible (which is why Microsoft still includes NetMeeting with XP). I discuss Microsoft's reasons for adopting SIP later. More important, however, is the improved videoconferencing experience with Windows Messenger, which results from enhancements in XP.

Microsoft has added to XP a new audio compression-decompression (codec) algorithm, called Siren, that it licensed from PictureTel. Siren can deliver better audio quality with high-bandwidth connections than NetMeeting codecs can. Siren offers two modes, both of which use a 16KHz sampling rate. A proprietary mode provides good audio quality at a 16Kbps bit rate; a G.722.1-compliant mode uses a 24Kbps bit rate and provides slightly better audio quality. When you initiate a videoconference, XP selects Siren's proprietary mode if the remote endpoint supports it; otherwise, XP attempts to use the G.722.1-compliant mode. Microsoft has also licensed PictureTel's acoustic echo-cancellation technology, which eliminates the retransmission of received audio without requiring conference participants to wear headphones.

Windows Messenger also attempts to address the audio latency problem. Although Microsoft can't do much about network latency, the company claims to have optimized the audio-processing routines in XP, thereby reducing PC-induced latency.

Unfortunately, these XP features don't benefit you when you're using NetMeeting (as you might when you're conferencing with someone who's using an earlier version of Windows) because Microsoft hasn't done the NetMeeting development work needed to take advantage of these enhancements. Something else to consider is that Windows Messenger's video codecs support only 176 x 144 pixel resolution. When Microsoft will offer versions tuned for 352 x 288 pixels is unclear. NetMeeting's codecs support both resolutions.

When I tested Windows Messenger in XP Release Candidate 1 (RC1), videoconference audio quality was noticeably better with high-bandwidth connections than it was with NetMeeting, and the echo-cancellation technology worked very well. Audio synchronization was also good, and I appreciated needing only one application rather than two (NetMeeting and MSN Messenger) to initiate and conduct the conference. Windows Messenger's application-sharing and whiteboard features work similarly to those features in NetMeeting.

Initially, Windows Messenger's videoconferencing features might not seem important, especially because the features are useful only when both parties are using XP. But as XP's installed base grows, Windows Messenger will make videoconferencing an increasingly attractive alternative to in-person meetings.

Microsoft feels that the SIP used in Windows Messenger offers advantages that will speed SIP's adoption by other vendors and ultimately will enable a broader range of conferencing options. One advantage is that SIP works well with other Web service protocols and technologies such as XML that, when combined with XP's realtime communications APIs, will let developers more easily integrate voice, video, and data conferencing into other applications. Another benefit is that third parties will be able to use those APIs to develop complementary products, such as Multipoint Control Units (MCUs) and Windows Messenger—compatible clients, for other Windows versions. Finally, compared with H.323, SIP has low resource requirements, which makes it attractive to cell-phone and PDA manufacturers. This feature will become more important as high-speed wireless services emerge that let mobile users participate in videoconferencing.