12.1 Introduction

Chapter 10 described how H.323 started life in the mid-1990s when ITU-T SG 16 started work on an umbrella recommendation for offering multimedia services over packet-based networks. The intention for H.323 was to create a framework that would allow multimedia services to be offered over LAN-based networks where quality of service was not an issue. This was based on the older H.320 recommendation that addressed the provision of multimedia services over ISDN-based switched-circuit networks. In keeping with this decision, ITU-T SG-16 adopted the call model, information elements and features of Q.931 and incorporated them into H.225.0 from the outset. They had also been working on H.324, a recommendation for offering multimedia services over dial-up connections. Since H.324 and H.323 require media and bearer control facilities, a common protocol, known as H.245, was developed to address the needs of both applications.

As the concept of offering real-time conversational services over packet networks entered mainstream thinking, the scope of H.323 [1] grew enormously to encapsulate many different applications. As a consequence, H.323 started to become more complex, containing a large set of annexes describing new protocol features and procedures, as described further in Chapter 10. To mitigate this growth in complexity, a number of profiles of H.323 have been created by industry groups such as the IMTC in addition to ETSI TIPHON and the ITU-T SG16 itself in the form of H.323 Annex F.

Around the same time as the ITU-T were developing H.323, the IETF's MMUSIC Working...