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

2. Outline Introduction Protocol Stack Elements Call signalling procedures 2

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

4. Protocol Stack 4

5. 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

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

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

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

9. Gatekeeper Optional element H.225.0 RAS – Address Translation – Admissions Control – Bandwidth Control – Zone Management – Optional Call Control signalling Call Management 9

10. 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

11. MC, MP, MCU 11

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

13. 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) 13

14. 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

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

16. Phase A: Call setup Caller routed call 16

17. Phase A: Call setup Callee routed call 17

18. 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

19. 19

20. 20

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

22. Phase C: Establishment of audiovisual communication 22

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

24. 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 24

25. Phase E: Call termination Call clearing with a gatekeeper 25

26. Phase E: Call termination Call clearing by gatekeeper 26

27. 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. 27

28. Thanks for Listening Q&A 28