entive for deployed systems to upgrade. Also, the availability of com- mercial SIP to H.323 signaling gateways allows both networks to work together and complete calls [4, 5]. The videoconferencing market is dominated by PSTN ISDN devices, which have been deployed since 1990. Since H.323 shares the same heritage, it Comparison to H.323 was designed to easily interwork with these existing systems. SIP was not designed to interwork with these systems and was also not designed specifically with video in mind. In fact, some key signaling components needed to do video conferencing are still not fully standardized in the IETF, although there is active work to finalize these standards. As a result, a fully functional, standards-based SIP videoconferencing system is not currently available (but will be soon). How- ever, the deployment of videoconferencing systems has been disappointing com- pared to many predictions of this useful technology. This largely has to do with bandwidth and cost factors. Now that bandwidth and camera costs are falling, SIP is well positioned to handle much simpler videoconferencing systems enabled by PCs with cheap Webcams. It is likely that SIP will play a bigger role in these future software-based video systems than the current dedicated hard- ware videoconferencing systems. In this way, SIP may in the future be a major player in the videoconferencing market but without ever displacing the current installed base. The major strength of SIP is that it is still relatively simple-it is an Inter- net protocol based on the Internet's architecture. While complex architectures have been developed using a multitude of SIP extensions, it is likely that these systems will be the exception rather than the rule. Most SIP end points will only need to support the base SIP specification and perhaps a few call control exten- sions to provide a wide variety of useful and innovative services. 8.5 Conclusion This chapter has introduced H.323 and discussed and compared it to SIP. While there are some similarities