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H323 Overview <한울타리> 최성철 http://hutr.ah.to/ Agenda 1. What is H.323? 2. H323 components 3. Protocols Specified by H.323 4. Terminal Characteristics 5. Gatekeeper Characteristics 6. Connection Procedures http://hutr.ah.to/ What is H.323? The H.323 standard is cornerstone technology for the transmission of real-time audio, video and data communications over packet-based networks. It specifies communication over packet-based networks(IP-based) or Internet packet(IPX) exchangebased local area networks(LANS), enterprise networks(ENs), metropolitan-area networks(MANs), and wide-area networks(WANs) Be applied in a variety of mechanisms – IP telephpony, videotelephony, etc.. Be applied to multipoint-multimedia communications. http://hutr.ah.to/ Interoperability of H.323 Terminals Scope of H.323 H.323 Terminal H.323 MCU Non-Guaranteed QoS LAN (Note) H.323 Gatekeeper H.323 Gateway Guaranteed GSTN H.323 Terminal N-ISDN H.323 Terminal B-ISDN QOS LAN H.310 terminal operating in H.321 mode V.70 Terminal H.324 Terminal http://hutr.ah.to/ Speech Terminal H.322 Terminal Speech Terminal H.320 Terminal H.321 Terminal Note: A gateway may support one or more of the GSTN, N-ISDN and/or B-ISDN connections. H.321 Terminal H.323 components Terminal MCU Gateway H.323 Terminal Terminal http://hutr.ah.to/ H.323 components -Terminals Used for real-time bidirectional multimedia communications. Can be a PC or stand-alone device, running an H.323 and the multimedia applications. Supports audio communications and can optionally support video or data communications. (basic service provided by an H.323 terminal is audio comm, an H.323 terminal plays a key role in IP-telephony services.) The primary goal of H.323 is to interwork with other multimedia terminals. http://hutr.ah.to/ H.323 components - Gateways Connects two dissimilar networks. Provides connectivity between an H.323 network and a non-H.323 network. Can connect and provide comm between H.323 terminal and SCN(switched telephony networks e.g., public switched telephone network(PSTN)). This connectivity of dissimilar networks is achieved by translating protocols for call setup and release, converting media formats between different networks, and transferring information between the networks connected by the gateway. http://hutr.ah.to/ H323 components - Gatekeepers Can be considered the brain of the H.323 network. Provide important services such as addressing, authorization and authentication of terminals and gateways. Provide bandwidth management, accounting, billing, and charging., May also provide call-routing services. http://hutr.ah.to/ H.323 components - MCU Multipoint Control Unit Provide support for conferences of three or more H.323 terminals. All terminals participating in the conference establish a connection with the MCU. The MCU manages conference resources, negotiates between terminals for the purpose of determining the audio or video coder/decoder to use. http://hutr.ah.to/ Protocols Specified by H.323 (1) Audio Codecs Video Codecs H.225 registration, admission, and status(RAS) H.225 call signaling H.245 control signaling Real-time transfer protocol(RTP) Real-time control protocol(RTCP) http://hutr.ah.to/ Protocols Specified by H.323 (2) http://hutr.ah.to/ Terminal Characteristics(1) H.225 Registration, Admission, and Status RAS is the protocol between endpoints (terminals and gateways) and gatekeepers. RAS is used to perform registeration, admission control, bandwidth changes, status, and disengage procedures between endpoints and gatekeepers. H.225 Call signaling Be used to establish a connection between two H.323 endpoints. Be achieved byu exchanging H.225 protocol message on the call signaling channel. http://hutr.ah.to/ Terminal Characteristics(2) H.245 Control Signaling Capabilities exchange Opening and closing of logical channels used to carry media streams Flow-control messages General commands and indications. RTP/RTCP Provides end-to-end delivery services of realtime audio and video. Be typically used to transport data via the user datagram protocol(UDP). Provides payload-type, sequence numbering, timestamping and delivery monitoring. Function of RTCP is to provide feedback on the quality of data distribution. http://hutr.ah.to/ Gatekeeper Characteristics(1) http://hutr.ah.to/ Gatekeeper Characteristics(2) Address Translation Calls originating within an H.323 network may use an alias to address the destination terminal. Admission Control Control the admission of the endpoints into the H.323 Uses RAS messages, ARQ, ACF, ARJ Bandwidth Control Provides support for bandwidth control by using the RAS message, BRQ, BCF, BRJ. Call-control Signaling (opt.) Route call-signaling message between H.323 endpoints. Call Authorization (opt.) GK may accept or reject the call. The reasons for rejection may include access-based or time-based restrictions, to and from particular terminals or gateways, Call Management (opt.) Maintain information about all active H.323 calls. http://hutr.ah.to/ Connection Procedures(1) http://hutr.ah.to/ Connection Procedures(2) http://hutr.ah.to/ Both Gatekeepers Routing Call Endpoint 1 Gatekeeper 2 Gatekeeper 1 Endpoint 2 ARQ(1) ACF(2) Setup(3) Setup(4) Call Proceeding(5) Call Proceeding(5) ARQ(6) ARJ(7) Facility(8) Release Complete(9) Setup(10) Setup(11) Call Proceeding(5) Call Proceeding(5) ARQ(12) ACF/ARJ(13) Alerting(14) Alerting(14) Alerting(14) Connect(15) Connect(17) RAS Messages Call Signalling Messages http://hutr.ah.to/ Connect(16) Question ? H.323 H.225 H.245 RTP/RTCP Gatekeeper Gateway Terminal MCU http://hutr.ah.to/