Service development and deployment in H.323 and SIP

Among the different solutions providing multimedia teleconferencing services over IP networks, two approaches are of major importance: H.323 standardized by the ITU-T and SIP standardized by the IETF. Some comparisons on a system level have been published, but the service architectures have rarely been addressed in the literature. In the near future an important driver for multimedia business will be the services and the mechanisms for their fast and efficient service development and deployment. We provide a comparison of the methods to implement services in SIP and H.323 focusing on the service architectures and their capabilities regarding the implementation of new features. While H.323 is still the more mature standard-albeit SIP tends to keep up-the two protocols have basic differences in the supplementary services architectures. H.323/H.450 has been defined as a sophisticated enterprise solution and is well suited to support complex multimedia calls involving widely interoperable supplementary services. SIP on the other side represents a more universal approach. SIP uses more generic syntax and semantics regarding feature definition and session description, which carries the danger to cause interworking problems. The advantage of SIP is its general applicability for signaling non-VoIP sessions for example the establishment of a PSTN session as standardized in the PINT approach.