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Understanding the H.323 Protocol: Beyond VoIP

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This presentation covers the H.323 protocol, emphasizing its comprehensive role beyond just Voice over IP (VoIP). Attendees will learn about the four key components of an H.323 network—Terminals, Gateways, Multipoint Control Units (MCUs), and Gatekeepers—along with their functions. The main operations for establishing, maintaining, and terminating voice communication sessions will be explained, including control signaling, media control, and transport protocols. The integration of H.323 with the Public Switched Telephone Network (PSTN) will also be discussed.

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Understanding the H.323 Protocol: Beyond VoIP

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Presentation Transcript

  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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