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Presentation 6 – The H.323 Protocol

Presentation 6 – The H.323 Protocol. Objectives. At the end of this presentation, you will be able to:. Explain why H.323 involves much more than just VoIP. Identify the four components or entities in an H.323 network and explain the purpose of each.

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Presentation 6 – The H.323 Protocol

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  1. Presentation 6 – The H.323 Protocol

  2. Objectives At the end of this presentation, you will be able to:

  3. Explain why H.323 involves much more than just VoIP. • Identify the four components or entities in an H.323 network and explain the purpose of each. • Explain the main operations involved in establishing, maintaining, and terminating a voice communications session using the H.323 protocol. • Identify the control signaling, media control, and media transport protocols employed in the H.323 suite of protocols and briefly explain the purpose of each. • Explain how H.323 integrates with the PSTN.

  4. International Telecommunications Union (ITU) • An international organization within the United Nations System where governments and the private sector coordinate global telecom networks and services. • The leading publisher of telecommunication technology, regulatory and standards information. • Released the first major protocol for VoIP called H.323.

  5. The H.323 protocol is much broader than just VoIP. • A set of protocols designed for voice, video, and data conferencing. • A set of protocols designed to operate over a range of packet-based networks.

  6. Components of an H.323 System • Terminals • Gateways • Multipoint Control Units (MCU) • Gatekeepers End points

  7. H.323 terminal • Provides real-time, two-way voice, video and/or data communications with another terminal. • Common VoIP examples include computers acting as soft phones, IP phones, and PSTN telephones equipped with Analog Telephone Adapters (ATA). • May also communicate with a gateway or a multipoint control unit.

  8. H.323 Gateway • A device that translates between an H.323 terminal and a non-H.323 terminal. • Common examples include translating from H.323 to: • PSTN • ATM • ISDN

  9. Multipoint Control Unit (MCU) • Allows conferences between three or more endpoints. • Required for multipoint conferences. • Not required for single-endpoint to single endpoint communications.

  10. Gatekeeper • May authorize network access to terminals or gateways. • May control bandwidth allocation to terminals. • May offer address translation services.

  11. H.323 Control Media Transport TCP/IP Audio Codec H.225 H.245 Call Control RTP/RTCP UDP TCP Internet Protocol (IP) Data Link Layer Physical Layer

  12. Control Audio Codec H.225 H.245 H.323 Call Control RTP/RTCP UDP TCP Internet Protocol (IP) TCP/IP Data Link Layer Physical Layer

  13. H.225 Control Signaling • Establishes and tears down connections between H.323 endpoints. • Handles registration, admission, and status signals.

  14. H.245 Media Control • Manages the media streams between H.323 endpoints. • Insures that the media sent by one end can be understood by the other end.

  15. Media Transport H.323 Audio Codec H.225 H.245 Call Control RTP/RTCP UDP TCP TCP/IP Internet Protocol (IP) Data Link Layer Physical Layer

  16. Media Transport H.323 Audio Codec H.225 H.245 Call Control RTP/RTCP UDP TCP TCP/IP Internet Protocol (IP) Data Link Layer Physical Layer

  17. Major H.323 Operations • Discovery • Registration • Connection Setup • Capability Exchange • Logical Channel Exchange • Payload Transfer • Termination

  18. Discovery • The endpoint determines which gatekeeper to register with. • Gatekeepers act as traffic cops. • The endpoint sends a multicast message asking: “Is my gatekeeper out there?” • The gatekeeper replies: “I’m your gatekeeper and here is my address”

  19. Registration • Endpoint: “Can I join your zone?” • Gatekeeper: “First, tell me all about yourself.” • Endpoint: “Well I am an end-user terminal, my IP address is ____ and my aliases are _____ and _______.” • Gatekeeper: “Okay, your qualifications look good, so you’re in.”

  20. RAS Signaling B Internet Gatekeeper A Endpoint

  21. Connection Setup • Calling Endpoint: “Hey my human needs to talk with your human.” • Called Endpoint : “Okay, I have initiated the call establishment procedure.” • Calling Endpoint : “Great. I’m ringing your number.” • Called Endpoint : “I have answered and am ready to proceed.”

  22. Capability Exchange • Endpoints reveal their capabilities to each other. • Endpoints agree on a media transfer format that both sides can understand and handle. • Examples; Codec, bit rate, etc.

  23. Logical Channel Exchange • The two endpoints set up the media transport channels. • With two-party VoIP calls, two logical channels are established, one in each direction. • These are the channels that will carry the voice packets back and forth.

  24. Payload Transfer • Voice data from the codec is processed by the Real-Time Protocol (RTP) into RTP packets. • These packets are transported from the caller endpoint to the called endpoint via UDP and IP over the logical media channels established in the prior step.

  25. Termination • Occurs when the phone conversation is eventually finished. • Both sides release the logical channel and any other resources such as bandwidth that was set aside for the call.

  26. Major H.323 Operations • Discovery • Registration • Connection Setup • Capability Exchange • Logical Channel Exchange • Payload Transfer • Termination

  27. PSTN Gateway Internet A Endpoint

  28. Internet 1 Multipoint Control Unit (MCU) 2 3 A Endpoint

  29. H.323 Capabilities Video Voice Data Multi-media IP ATM Other ISDN Packet-Based Transport

  30. H.323 Criticisms • Too complex • Not easy to scale up • Not designed specifically with Internet Protocol (IP) in mind.

  31. End

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