H.323. Voice over IP. Bell Heads: ITU Int l Telecommunications Union. Data Geeks: Internet Engineering Task Force. IETF Jargon

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Agnes Dalton
5 years ago
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1 Voice over IP H.323 Adapted from Slides by Phil Campbell Voice over IP Fundamentals, Second Edition, by Jonathan Davidson; James Peters; Manoj Bhatia; Satish Kalidindi; Sudipto Mukherjee; Cisco Press, July 27, Bell Heads: ITU Int l Telecommunications Union Associated with UN Member states, associated companies No regulatory authority!!! FCC represents US at ITU. Telco bureaucrats? 2 Data Geeks: Internet Engineering Task Force loosely self-organized group of people who contribute to the engineering and evolution of Internet technologies The Tao of the IETF: No regulatory authority!!! Consensus seeking geeks?! 3 IETF Jargon RFC Request for Comment Series of documents, referred to by number Some are proposed standards, some are BCPs BCP Best Current Practice Consensus of IETF opinion See RFC 2026, The Internet Standards Process Revision 3 4

Real life? Vendors under no legal obligation to respect either ITU or IETF standards. They can and do: Selectively implement. Modify standards for implementation. Go beyond standards.

2 Real life? Vendors under no legal obligation to respect either ITU or IETF standards. They can and do: Selectively implement. Modify standards for implementation. Go beyond standards. Invent their own standards. Implement older versions of standards. Guess at outcome of standards process. Screw up. 5 H.323 ITU Standard (Bell Heads) Really a family of Standards Supports multimedia i.e. video Supports multipoint i.e. broadcast & conference Not originally intended for internet based on expected LAN/WAN usage. Player in CPE marketplace Declining? More common in video than voice 6 H.323 Terminology Endpoints Terminals Gateways Multipoint Control Units (MCUs) Gatekeeper Endpoints associated with a Gatekeeper form an H.323 Zone. Note: H.323 does not require use of a gatekeeper. 7 H.323 Elements 8

3 Inside the H.323 Terminal 9 The Protocol Stack 10 Protocol Functions H Signaling RAS - Registration, Admission, Status» Terminal and Gatekeeper Call Setup and Termination» Carries Q.931 (ISDN/ATM) call control messages H Media Control Start and stop logical media channels 11 H RAS For mediation among endpoints and gatekeepers Discovery Registration Name resolution: alias IP address Admission control Bandwidth control Status requests Uses UDP 12

4 H.225 RAS Messages RAS messages generally have three types Request (xrq) Reject (xrj) Confirm (xcf) Messages encoded using ASN.1 / PER Compressed format following a formal data structure definition. (Not human-friendly). 13 H.225 Gatekeeper Discovery Std messages: GRQ: Gatekeeper Request GCF: Gatekeeper Confirm GRJ: Gatekeeper Reject Gatekeeper Selection Multicast GRQ DHCP Manually configured Gatekeeper can ignore/reject GRQ 14 H.225 Registration Std messages: RRQ: Registration Request RCF: Registration Confirm RRJ: Registration Reject 15 Registration Process Endpoint requests registration. GK can ignore request. GK can check MAC address of endpoint. GK gives identifier to endpoint. Used during subsequent exchanges with the gatekeeper Endpoint supplies list of aliases Phone #, , etc. Gatekeeper indicates acceptance in RCF. 16

5 Also During Registration Gatekeeper may grant endpoint permission to place calls without using the ARQ/ACF exchange. The endpoint indicates a time to live for the registration. Gatekeeper accepts or reduces. 17 Call Setup Note: Looks a bit like the SIP triangle Gatekeeper and SIP proxy have somewhat similar functions. 18 More Detail 19 MCUs Rebroadcast of audio/visual/data streams Conference Control Who can participate? Joining/departing conference, etc. Content Mixing Changing audio/visual combinations Audio mix, video frame construction Real-Time Transcoding Different participants with different codecs 20

The H.323 protocol suite. How works one of the protocol architectures for VoIP

The H.323 protocol suite. How works one of the protocol architectures for VoIP The H.323 protocol suite How works one of the protocol architectures for VoIP 1 Basic characteristics Standard for LAN communication Packet switched networks without guaranteed quality Extended to operate