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Miroslav Voznak, lecture on H.3231 Miroslav Vozňák VŠB - Technical University of Ostrava Department of Telecommunications Faculty of Electrical Engineering.

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Presentation on theme: "Miroslav Voznak, lecture on H.3231 Miroslav Vozňák VŠB - Technical University of Ostrava Department of Telecommunications Faculty of Electrical Engineering."— Presentation transcript:

1 Miroslav Voznak, lecture on H.3231 Miroslav Vozňák VŠB - Technical University of Ostrava Department of Telecommunications Faculty of Electrical Engineering and Computer Science 17. listopadu 15, Ostrava – Poruba Lecture No.5 Call signaling flow, H.245 Slow Start, Fast Connect and tunneling /1: Voice over IP

2 Miroslav Voznak, lecture on H.3232 Call Flow Q.931 and H.245 a normal method defined in the 1 st 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

3 Miroslav Voznak, lecture on H.3233 Call Flow - Q.931 and H.245 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 Initiate a new call

4 Miroslav Voznak, lecture on H.3234 Call Flow - Q.931 and H.245 Q.931 CALL PROCEEDING q931.call_ref = 50:A4, h225.t35CountryCode = 0 The called subscriber responds with a Q.931 CALL PROCEEDING indication. Q.931 ALERTING 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. Ring back tone

5 Miroslav Voznak, lecture on H.3235 Call Flow - Q.931 and H.245 Answer call Q.931 CONNECT H245_IP_Address, H245_Port = Called H245 Port, q931.call_ref = 50:A4, h225.t35CountryCode = 0 The Q.931 connect is sent to the caller. The message contains information about the H.245 negotiation port. An H.245 session will now be established The calling H.245 port information is extracted from the connect message.

6 Miroslav Voznak, lecture on H.3236 Call Flow - Q.931 and H.245 H.245 Terminal Capability Set Request receive_audio_capability = (G.711, A-law, 64Kbps) Now establish a TCP connection for H.245 negotiation. Called party negotiates terminal capability. G.711 A-law 64Kbps codec is requested. Called party negotiates master-slave. H.245 Master Slave Determination Request

7 Miroslav Voznak, lecture on H.3237 Call Flow - Q.931 and H.245 H.245 Terminal Capability Set Request receive_audio_capability = (G.711, A-law, 64Kbps) Calling party also negotiates terminal capability. G.711 A-law 64Kbps codec is requested. Caller also initiates a Master Slave determination request. H.245 Master Slave Determination Request

8 Miroslav Voznak, lecture on H.3238 Call Flow - Q.931 and H.245 H.245 Terminal Capability Set Ack + Master Slave Determination Ack sequence_number = 1, decision = Slave Caller replies with a combined "terminal capability" and "master-slave" ack. 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

9 Miroslav Voznak, lecture on H.3239 Call Flow - Q.931 and H.245 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 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 = 61, audio_data = (G.711, A-law, 64Kbps), media_control_ip_address, tsap_Identifier = Called 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.

10 Miroslav Voznak, lecture on H Call Flow - Q.931 and H.245 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 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 = 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.

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

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

13 Miroslav Voznak, lecture on H.32313

14 Miroslav Voznak, lecture on H H 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

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

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

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

18 Miroslav Voznak, lecture on H.32318

19 Miroslav Voznak, lecture on H H 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.

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

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

22 Miroslav Voznak, lecture on H FACILITY TCS Acknowledge MSD Acknowledge

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

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

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

26 Miroslav Voznak, lecture on H CONNECT Media immediately after OLC Ack = Early Media 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

27 Miroslav Voznak, lecture on H 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)

28 Miroslav Voznak, lecture on H Thank you for your attention


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