Speaker: Yi-Lei Chang Advisor: Dr. Kai-Wei Ke 2012/11/28 H.323 Packet-based multimedia communications systems 1

Outline Introduction Protocol Stack Elements Call signalling procedures 2

Introduction 1996 ITU-T (Telecommunication Standardization sector of International Telecommunication Union) Packet-based multimedia communications systems 3

Protocol Stack 4

Additional Documents H.235Security within H.245-based systems H.450.xSupplementary services H.460.xVarious H.323 protocol extensions H.501Protocol for mobility management and inter/intra-domain communication H.510User, terminal, and service mobility H.530Security specification for H.510 5

Elements Terminals Gateways Gatekeeper MC, MP, MCU – Multipoint controller – Multipoint processor – Multipoint control unit 6

Terminals Telephones, Video phones, etc. Soft phones G.711 (voice) H.261 (video, optional) 7

Gateway Interface H.323 to other networks – PSTN – H.320 systems – other H.323 networks (proxy) – etc. 8

Gatekeeper Optional element H RAS – Address Translation – Admissions Control – Bandwidth Control – Zone Management – Optional Call Control signalling Call Management 9

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 10

MC, MP, MCU 11

H 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:GatekeeperR:Registration A:AdmissionsL:Location D:DisengageU:Unregistration IRQ (Information Request), IRR (Information Request Response) 12

Call signalling procedures Phase A: Call setup. – H.225.0/Q.931 Call control, H 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 RAS (if reg. to a gatekeeper) 13

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: 14

Phase A: Call setup Caller/Callee registered to Gatekeeper 15

Phase A: Call setup Caller routed call 16

Phase A: Call setup Callee routed call 17

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 18

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Phase B: Initial communication and capability exchange Capability exchange Master Slave Determination 21

Phase C: Establishment of audiovisual communication 22

Phase D: Call services Status – IRQ, IIR – Interval > 10 sec. Bandwidth changes – BRQ, BCF, BRJ – closeLogicalChannel, openLogicalChannel, flowControlCommand Conference expansion – Create – Invite – Join 23

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 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 24

Phase E: Call termination Call clearing with a gatekeeper 25

Phase E: Call termination Call clearing by gatekeeper 26

Reference [1] International Telecommunication Union, "Packet-based Multimedia Communications Systems," Recommendation H.323, Telecommunication Standardization Sector of ITU, December [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 [3] International Telecommunication Union, "Control protocol for multimedia communication," Recommendation H.245, Telecommunication Standardization Sector of ITU, May

Thanks for Listening Q&A 28