VoIP services and IP-based communications services, such as the IP-PBX, leverage protocols to carry audio, video, and data. The two most popular VoIP protocols are H.323 and SIP. For detail on these protocols, visit the Internet Engineering Task Force (IETF) via its Web site at http://www.ietf.org searching for RFC 2543 for SIP, and the International Telecommunications Union (ITU-T) Web site via http://www.itu.int for details on H.323. As depicted in the figures earlier in this chapter, SIP is the standard VoIP protocol used to carry audio, video, and data communications and is the protocol that Microsoft chose to build its communication platform of products on due to the ability to provide more flexibility and customization in how audio, video, and data are handled between applications (see Figure 1.8). H.323 was the previous industry standard, but based on its rigidness and lack of flexibility, was not the protocol of choice. Another major reason why H.323 was not chosen has to do with bandwidth. The goal of VoIP is to work within ubiquitous networks and lower the overall threshold of the communication pipe to lower bandwidth requirements enabling lightweight applications and devices that leverage VoIP.
Figure 1.8 SIP architecture
Leveraging SIP as the foundation protocol for VoIP enables Microsoft to build communications products that carry the richness of audio, video, and data as well as provide the capability of custom application development to enhance these SIP-based products using third-party integrated solutions from Microsoft’s worldwide partner community. In the future, as expressed in my hypothetical 2010 scenario described earlier in this chapter, these flexible and feature-rich solutions will be extended to mobile users leveraging SIP over wireless broadband networks such as WiMax towers that spread a broadband Internet connection across entire regions. Like you see in Japan and in spy movies, you will be able to communicate, via mobile, audio, video, and data without using your mobile wireless carrier network, saving you time and at a fraction of the cost.