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H 323 and Associated Protocols H 323 and Associated Protocols Asim Karim karim 7 osu edu Abstract H 323 is an ITU T recommendation for multimedia conferencing over packet based networks such as LANs and the Internet H 323 is broad and comprehensive in its scope yet flexible and practical in its applicability This report describes the components protocols and procedures in H 323 the challenges to the widespread adoption of H 323 the outlook for H 323 as a standard for multimedia conferencing and key H 323 products and services See Also Voice Over IP Lecture by Prof Jain Internet Telephony Voice Over IP Protocols and Standards Voice Over IP Products Services and Issues Multimedia Networking Products Voice Over IP References Books on Voice Over IP Other Reports on Recent Advances in Networking Back to Raj Jain s Home Page Table of Contents 1 Introduction 2 Scope of H 323 3 Why is H 323 Important 4 H 323 Architecture Components 4 1 Terminal 4 2 Gateway 4 3 Gatekeeper 4 4 Multipoint Control Unit MCU 5 H 323 Architecture Protocols and Procedures 5 1 H 323 Terminal Protocol Stack 5 2 Audio Codecs G 711 G 722 G 723 1 G 728 G 729 5 3 Video Codecs H 261 H 263 5 4 Data Conferencing T 120 5 5 Control and Signaling Mechanisms H 225 0 H 245 H 225 0 RAS 5 6 Call Setup and Tear Down 5 7 Supplementary Services H 450 x 5 8 Security H 235 6 Challenges 6 1 Interoperability and Implementation Issues 6 2 Lack of Value Added Services 6 3 Quality and Security Issues 7 Future Prospects 7 1 H 323 or SIP 7 2 Trends in the Enterprise Market 7 3 Trends in the Home and Small Business Markets 7 4 Future Developments in H 323 8 Products and Services http www cis ohio state edu jain cis788 99 h323 index html 1 of 19 2 7 2000 10 40 28 AM H 323 and Associated Protocols 8 1 MCUs 8 2 ITSPs 9 Summary References List of Acronyms 1 Introduction Recommendation H 323 is a set of protocols for voice video and data conferencing over packet based networks such as the Internet The current recommendation known as version 2 0 was ratified by the Study Group 16 SG16 of the Telecommunications Sector of the International Telecommunication Union ITU T The H 323 protocol stack is designed to operate above the transport layer of the underlying network As such H 323 can be used on top of any packet based network transport like Ethernet TCP UDP IP ATM and Frame Relay to provide real time multimedia communication H 323 uses the Internet Protocol IP for inter network conferencing H 323 is one of several videoconferencing recommendations issued by ITU T The other recommendations in the series include H 310 for conferencing over broadband ISDN B ISDN H 320 for conferencing over narrowband ISDN H 321 for conferencing over ATM H 322 for conferencing over LANs that provide a guaranteed quality of service and H 324 for conferencing over public switched telephone networks PSTN The H 323 standard is designed to allow clients on H 323 networks to communicate with clients on the other videoconferencing networks This report provides a detailed overview of the components protocols and procedures defined in H 323 The technical challenges facing the widespread adoption of H 323 the current extensions and developments in H 323 and the future prospects of H 323 as a videoconferencing standard are also discussed Back to Table of Contents 2 Scope of H 323 H 323 is a broad and flexible recommendation As a minimum H 323 specifies protocols for real time point to point audio communication between two terminals on a packet based network that do not provide a guaranteed quality of service The scope of H 323 however is much broader and encompasses inter network multipoint conferencing among terminals that support not only audio but also video and data communication The scope of Recommendation H 323 can be summarized in the following broad categories Point to point and multipoint conferencing support H 323 conferences may be set up between two or more clients without any specialized multipoint control software or hardware However when a multipoint control unit MCU is used H 323 supports a flexible topology for multipoint conferences A multipoint conference may be centralized where new participants can join all the others in the conference This is the so called hub and spoke topology Or a multipoint conference may be decentralized where new participants can elect to join one or more participants in the conference but not all This approach will produce a flexible tree topology Inter network interoperability H 323 clients are interoperable with switched circuit network SCN conferencing clients such as those based on Recommendations H 320 ISDN H 321 ATM and H 324 PSTN Wireless Heterogeneous client capabilities A H 323 client must support audio communication video and data support is optional This heterogeneity and flexibility does not make the clients incompatible During call set up capabilities are exchanged and communication established based on the lowest common denominator Audio and video codecs H 323 specifies a required audio and video codec However there is no restriction on the use of other codecs and two clients can agree on any codec which is supported by both of them Management and accounting support H 323 calls can be restricted on a network based on the number of calls already in progress bandwidth limitations or time restrictions Using these policies the network manager can manage H 323 traffic Further H 323 also provides accounting facilities that can be used for billing purposes Security H 323 provides authentication integrity privacy and non repudiation support Supplementary services Recommendation H 323 recognizes the huge potential for applications based on IP telephony and multimedia It provides a basic framework for development of such services In version 2 0 of H 323 two services call transfer and call forwarding have been specified http www cis ohio state edu jain cis788 99 h323 index html 2 of 19 2 7 2000 10 40 28 AM H 323 and Associated Protocols Back to Table of Contents 3 Why is H 323 Important Trend The explosive growth of the Internet and the almost universal deployment of corporate LANs have made packet based networks ubiquitous It is therefore natural for individuals and enterprises to use this resource for audio and video communication to offset some of the tariffs of public switched telephone networks PSTN Multimedia over packet based networks primarily IP networks has grown rapidly in the last few years Industry research put the


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