Miroslav Voz ňák VŠB - Technical University of Ostrava Department of Telecommunications

1. 454-319/1: Voice over IP Lecture No.5 Call signaling flow, H.245 Slow Start, Fast Connect and tunneling Miroslav Vozňák VŠB - Technical University of Ostrava Department of Telecommunications Faculty of Electrical Engineering and Computer Science 17. listopadu 15, 708 33 Ostrava – Poruba mailto:miroslav.voznak@vsb.cz http://homel.vsb.cz/~voz29 Miroslav Voznak, lecture on H.323

2. Call Flow Q.931 and H.245 • a normal method defined in the 1st version is called as Slow Start (obsolete) H.225 / Q.931 Call Signaling Channel H.245 Control Channel H.245 Logical Channel for RTP and RTCP Miroslav Voznak, lecture on H.323

3. Call Flow - Q.931 and H.245 Initiate a new call Call establishes a TCP connection for a new call, destination port is TCP 1720 A Q.931 SETUP message is sent once the TCP connection has been established. Q.931 SETUP source_address, source_port = Caller H225 Port, destination_address, destination_port = Called H225 Port, call_type = Point to Point, q931.call_ref = 50:A4, h225.t35CountryCode = 9 Miroslav Voznak, lecture on H.323

4. Call Flow - Q.931 and H.245 The called subscriber responds with a Q.931 CALL PROCEEDING indication. Q.931 CALL PROCEEDING q931.call_ref = 50:A4, h225.t35CountryCode = 0 Ring the called subscriber The Q.931 ALERTING message indicates that the called subscriber is now being rung. Q.931 ALERTING q931.call_ref = 50:A4, h225.t35CountryCode = 0 Ring back tone Miroslav Voznak, lecture on H.323

5. Call Flow - Q.931 and H.245 Answer call The Q.931 connect is sent to the caller. The message contains information about the H.245 negotiation port. Q.931 CONNECT H245_IP_Address, H245_Port = Called H245 Port, q931.call_ref = 50:A4, h225.t35CountryCode = 0 An H.245 session will now beestablished The calling H.245 port information is extracted from the connect message. Miroslav Voznak, lecture on H.323

6. Call Flow - Q.931 and H.245 Now establish a TCP connection for H.245 negotiation. H.245 Terminal Capability Set Request receive_audio_capability = (G.711, A-law, 64Kbps) Called party negotiates terminal capability. G.711 A-law 64Kbps codec is requested. H.245 Master Slave Determination Request Called party negotiates master-slave. Miroslav Voznak, lecture on H.323

7. Call Flow - Q.931 and H.245 Calling party also negotiates terminal capability. G.711 A-law 64Kbps codec is requested. H.245 Terminal Capability Set Request receive_audio_capability = (G.711, A-law, 64Kbps) H.245 Master Slave Determination Request Caller also initiates a Master Slave determination request. Miroslav Voznak, lecture on H.323

8. Call Flow - Q.931 and H.245 Caller replies with a combined "terminal capability" and "master-slave" ack. H.245 Terminal Capability Set Ack + Master Slave Determination Ack sequence_number = 1, decision = Slave Called party responds with terminal capability ack. H.245 Terminal Capability Set Ack sequence_number = 1 Called party becomes the master. H.245 Master Slave Determination Ack decision = Master Miroslav Voznak, lecture on H.323

9. Call Flow - Q.931 and H.245 Send channel open request to the called party. RTCP port number is included in the message. The G.711 A-law 64Kbps will be used on the audio path. H.245 Open Logical Channel Request channelNumber = 101, audio_data = (G.711, A-law, 64Kbps), media_control_ip_address, tsap_Identifier = Caller RTCP Port, silence_supression = TRUE Send channel open request to the calling party. RTCP port number is included in the message. The G.711 A-law 64Kbps will be used on the audio path. H.245 Open Logical Channel Request channelNumber = 61, audio_data = (G.711, A-law, 64Kbps), media_control_ip_address, tsap_Identifier = Called RTCP Port, silence_supression = TRUE Miroslav Voznak, lecture on H.323

10. Call Flow - Q.931 and H.245 Caller acknowledges the message. The RTP and RTCP port numbers are included in the message. H.245 Open Logical Channel Ack media_control_ip_address, media_control_tsap_identifier = Caller RTCP Port, media_ip_address, media_tsap_identifier = Caller RTP Port H.245 Open Logical Channel Ack media_control_ip_address, media_control_tsap_identifier = Called RTCP Port, media_ip_address, media_tsap_identifier = Called RTP Port Called party acknowledges the message. The RTP and RTCP port numbers are included in the message. Miroslav Voznak, lecture on H.323

11. too many messages ! Setup Call Proceeding Alerting Connect TCS Req. MSD Req. TCS Req. MSD Req. Miroslav Voznak, lecture on H.323

12. TCS Ack. MSD Ack. TCS Ack. MSD Ack. OLC Req. OLC Req. OLC Ack. RTP stream OLC Ack. RTP stream we need open logical channel earlier ! Miroslav Voznak, lecture on H.323

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14. H.245 - Fast Connect • added in version 2 • allows endpoints to open logical channel earlier • New fields – Fast Start element contains OLC (OpenLogicalChannel) proposals • Fast Start elements are carried in Q.931 messages • endpoint may refuse Fast Connect H.225 / Q.931 Call Signaling Channel with H.245 Fast Start elements H.245 Logical Channel for RTP and RTCP Miroslav Voznak, lecture on H.323

15. SETUP with Fast Start Element open logical channel • forward logical channel • without information • reverse logical channel • codec: g711Alaw, 20 ms • media channel = RTP • ipaddress: 158.196.81.114 • port: 49152 • media control channel = RTCP • ipaddress: 158.196.81.114 • port: 49153 Miroslav Voznak, lecture on H.323

16. CONNECT with Fast Start Element open logical channel forward logical channel • codec: g711Alaw, 20 ms • media channel = RTP • ipaddress: 158.196.81.101 • port: 49152 • media control channel = RTCP • ipaddress: 158.196.81.101 • port: 49153 Miroslav Voznak, lecture on H.323

17. SETUP withOLC Call Proceeding Alerting Connect with OLC TCS Req. TCS Req. MSD Req. MSD Req. TCS Ack. TCS Ack. MSD Ack. MSD Ack. RTP Miroslav Voznak, lecture on H.323

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19. H.245 - Tunneling Tunneling is the process of sending H.245 through the Q.931 channel. The same TCP/IP socket that is already in use for the Call Signalling Channel is also used by the H.245 Control Channel. More H.245 PDU may be sent in one Q.931 message. Miroslav Voznak, lecture on H.323

20. SETUP • TCS Request • protocol identifier: version • capability Table • three items • MSD Request Miroslav Voznak, lecture on H.323

21. ALERTING • TCS Request • MSD Request • TCS Acknowledge • MSD Acknowledge Miroslav Voznak, lecture on H.323

22. FACILITY • TCS Acknowledge • MSD Acknowledge Miroslav Voznak, lecture on H.323

23. FACILITY • OLC Request • forward logicalchannel Miroslav Voznak, lecture on H.323

24. FACILITY • OLC Acknowledge • Media channel • RTP Media unidirectional • OLC Request • Media control channel Miroslav Voznak, lecture on H.323

25. FACILITY • OLC Acknowledge • Media channel • RTP Media bidirectional Miroslav Voznak, lecture on H.323

26. Media immediately after OLC Ack = Early Media CONNECT Close Logical Channel, CLC Request, Acknowledge End Session Command, ESC Request, Acknowledge possibility any H.245 PDU sends through FACILITY Closing the H.245 Control Channel – endpoits must: • CLC Req. - close all open logical channels • CLC Ack. - wait for all acknowledgement messages • ESC - send an End Session and wait for End Sesion from the other side Miroslav Voznak, lecture on H.323

27. Conclusion H.245 Slow Start – old method, H.323v1, separate TCP connection, a lot of H.245 messages are carried via a special H.245 Control Channel H.245 Fast Start –H.323v2, media can be negotiated via Fast Connect (OLC in Fast Start elements), each OLC represents a proposed channel in either forward or the reverse direction, H.245 Tunneling - generally supported by the newer endpoints, H.245 PDUs are placed inside Q.931 Early Media – RTP starts immediately after negotiated parameters for RTP (OLC Ack) Miroslav Voznak, lecture on H.323

28. Thank you for your attentionmiroslav.voznak@vsb.cz Miroslav Voznak, lecture on H.323