Speaker: Yi-Lei ChangAdvisor: Dr. Kai-Wei Ke

2012/11/28

H.323 Packet-based multimedia communications systems

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Outline

• Introduction• Protocol Stack• Elements• Call signalling procedures

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Introduction

• 1996 • ITU-T

(Telecommunication Standardization sector of International Telecommunication Union)

• Packet-based multimedia communications systems

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Protocol Stack

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Additional Documents

• H.235 Security within H.245-based systems• H.450.x Supplementary services• H.460.x Various H.323 protocol extensions• H.501 Protocol for mobility management

and inter/intra-domain communication

• H.510 User, terminal, and service mobility• H.530 Security specification for H.510

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Elements

• Terminals• Gateways• Gatekeeper• MC, MP, MCU– Multipoint controller– Multipoint processor– Multipoint control unit

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Terminals

• Telephones, Video phones, etc.• Soft phones• G.711 (voice)• H.261 (video, optional)

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Gateway

• Interface H.323 to other networks– PSTN– H.320 systems– other H.323 networks (proxy)– etc.

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Gatekeeper

• Optional element• H.225.0 RAS– Address Translation– Admissions Control– Bandwidth Control– Zone Management– Optional• Call Control signalling• Call Management

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MC, MP, MCU• Multipoint controller– Provides control functions to support conferences

between three or more endpoints in a multipoint conference

• Multipoint processor– Handle media mixing, switching, or other media

processing• Multipoint control unit– An endpoint which provides support for multipoint

conferences– The MCU shall consist of an MC and zero or more MPs

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MC, MP, MCU

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H.255.0 RAS• Registration, Admission, and Status• Used between the endpoint and its Gatekeeper• RAS Port

– 1719 (unicast)– 1718 (multicast) for GRQ, LRQ

• RAS messages generally have three types– Request (xRQ)– Reject (xRJ)– Confirm (xCF)– x can be

• G:Gatekeeper R:Registration• A:Admissions L:Location• D:Disengage U:Unregistration

• IRQ (Information Request), IRR (Information Request Response)

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Call signalling procedures

• Phase A: Call setup.– H.225.0/Q.931 Call control , H.225.0 RAS (if reg. to a gatekeeper)

• Phase B: Initial communication and capability exchange– H.245 Multimedia control, H.225.0/Q.931 Call control

• Phase C: Establishment of audiovisual communication– H.245 Multimedia control, RTP, RTCP

• Phase D: Call services– Status, Bandwidth changes, Conference expansion

• Phase E: Call termination– H.225.0/Q.931 Call control, H.245 Multimedia control (optional),

H.225.0 RAS (if reg. to a gatekeeper)

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Phase A: Call setup• Notify user, setup H.245 channel• Caller/Callee registered to Gatekeeper?• Routed/direct call? (if reg. to a Gatekeeper)• Simple call setup:

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Phase A: Call setupCaller/Callee registered to Gatekeeper

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Phase A: Call setupCaller routed call

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Phase A: Call setupCallee routed call

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Phase A: Call setupAn example

• Endpoint 1 – registered to gatekeeper 1

• Gatekeeper 1– use direct call

• Endpoint 2– registered to gatekeeper 2

• Gatekeeper 2– use routed call

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Phase B: Initial communication and capability exchange

• Capability exchange• Master Slave Determination

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Phase C: Establishment of audiovisual communication

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Phase D: Call services• Status– IRQ, IIR– Interval > 10 sec.

• Bandwidth changes– BRQ, BCF, BRJ– closeLogicalChannel, openLogicalChannel,

flowControlCommand• Conference expansion– Create– Invite– Join

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Phase E: Call termination• Terminate a call– Discontinue transmission of video, data, audio and then

close all logical channels for them– Transmit the H.245 endSessionCommand (optional)– Close H.245 Control Channel– Transmit a Release Complete message and close the

H.225.0 call signalling channel• Terminate a conference– H.245 message dropConference– Wait for MC to terminate calls

• Call clearing with a gatekeeper• Call clearing by gatekeeper

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Phase E: Call terminationCall clearing with a gatekeeper

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Phase E: Call terminationCall clearing by gatekeeper

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Reference[1] International Telecommunication Union, "Packet-based Multimedia Communications Systems," Recommendation H.323, Telecommunication Standardization Sector of ITU, December 2009.

[2] International Telecommunication Union, "Call signalling protocols and media stream packetization for packet-based multimedia communication systems," Recommendation H.225.0, Telecommunication Standardization Sector of ITU, December 2009.

[3] International Telecommunication Union, "Control protocol for multimedia communication," Recommendation H.245, Telecommunication Standardization Sector of ITU, May 2011.

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Thanks for Listening

Q&A

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