H.323 Packet-based multimedia
communications systems
Speaker: Yi-Lei Chang
Advisor: Dr. Kai-Wei Ke
2012/11/28
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Outline
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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
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H.235
H.450.x
H.460.x
H.501
• H.510
• H.530
Security within H.245-based systems
Supplementary services
Various H.323 protocol extensions
Protocol for mobility management
and inter/intra-domain
communication
User, terminal, and service mobility
Security specification for H.510
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Elements
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Terminals
Gateways
Gatekeeper
MC, MP, MCU
– Multipoint controller
– Multipoint processor
– Multipoint control unit
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Terminals
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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
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Request (xRQ)
Reject (xRJ)
Confirm (xCF)
x can be
• G:Gatekeeper
• A:Admissions
• D:Disengage
R:Registration
L:Location
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
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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 setup
Caller/Callee registered to Gatekeeper
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Phase A: Call setup
Caller routed call
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Phase A: Call setup
Callee routed call
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Phase A: Call setup
An 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 termination
Call clearing with a gatekeeper
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Phase E: Call termination
Call 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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