miroslav voznak, lecture on h.3231 miroslav vozňák vŠb - technical university of ostrava...
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Miroslav Voznak, lecture on H.323
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Miroslav VozňákVŠB - Technical University of OstravaDepartment of Telecommunications
Faculty of Electrical Engineering and Computer Science
17. listopadu 15, 708 33 Ostrava – Poruba
mailto:[email protected] http://homel.vsb.cz/~voz29
Lecture No.5 Call signaling flow, H.245 Slow
Start, Fast Connect and tunneling
454-319/1: Voice over IP
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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
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Call Flow - Q.931 and H.245
Call establishes a TCP connection for anew call, destination port is TCP 1720
A Q.931 SETUP message is sent oncethe TCP connection has beenestablished.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
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Call Flow - Q.931 and H.245
Q.931 CALL PROCEEDINGq931.call_ref = 50:A4,h225.t35CountryCode = 0
The called subscriber responds with aQ.931 CALL PROCEEDING indication.
Q.931 ALERTINGq931.call_ref = 50:A4,h225.t35CountryCode = 0
Ring the called subscriber
The Q.931 ALERTING messageindicates that the called subscriber isnow being rung.
Ring back tone
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Call Flow - Q.931 and H.245
Answer call
Q.931 CONNECTH245_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 informationabout the H.245 negotiation port.
An H.245 session will now be established
The calling H.245 portinformation is extracted from theconnect message.
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Call Flow - Q.931 and H.245
H.245 Terminal Capability Set Requestreceive_audio_capability = (G.711, A-law, 64Kbps)
Now establish a TCP connection forH.245 negotiation.
Called party negotiates terminalcapability. G.711 A-law 64Kbps codecis requested.
Called party negotiates master-slave.H.245 Master Slave Determination Request
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Call Flow - Q.931 and H.245
H.245 Terminal Capability Set Requestreceive_audio_capability = (G.711, A-law, 64Kbps)
Calling party also negotiates terminalcapability. G.711 A-law 64Kbps codecis requested.
Caller also initiates a Master Slavedetermination request.
H.245 Master Slave Determination Request
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Call Flow - Q.931 and H.245
H.245 Terminal Capability Set Ack + Master Slave Determination Acksequence_number = 1,decision = Slave
Caller replies with a combined "terminalcapability" and "master-slave" ack.
Called party responds with terminalcapability ack.
H.245 Terminal Capability Set Acksequence_number = 1
Called party becomes the master.H.245 Master Slave Determination Ackdecision = Master
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Call Flow - Q.931 and H.245
H.245 Open Logical Channel RequestchannelNumber = 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 thecalled party. RTCP port number isincluded in the message. The G.711A-law 64Kbps will be used on the audiopath.
H.245 Open Logical Channel RequestchannelNumber = 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 thecalling party. RTCP port number isincluded in the message. The G.711A-law 64Kbps will be used on the audiopath.
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Call Flow - Q.931 and H.245
H.245 Open Logical Channel Ackmedia_control_ip_address,media_control_tsap_identifier = Caller RTCP Port,media_ip_address,media_tsap_identifier = Caller RTP Port
Caller acknowledges the message. TheRTP and RTCP port numbers areincluded in the message.
H.245 Open Logical Channel Ackmedia_control_ip_address,media_control_tsap_identifier = Called RTCP Port,media_ip_address,media_tsap_identifier = Called RTP Port
Called party acknowledges themessage. The RTP and RTCP portnumbers are included in the message.
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too many messages !
Setup
Call Proceeding
Alerting
Connect
TCS Req.
MSD Req.
TCS Req.
MSD Req.
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TCS Ack. MSD Ack.
TCS Ack.
MSD Ack.
OLC Req.
OLC Req.
OLC Ack.
OLC Ack.
we need open logical channel earlier !
RTP stream
RTP stream
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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
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SETUP with Fast Start Element
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
open logical channel
forward logical channel
• without information
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• 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
open logical channel
forward logical channel
CONNECT with Fast Start Element
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SETUP with OLC
Call Proceeding
Alerting
Connect with OLC
TCS Req.
TCS Req.
MSD Req.
MSD Req.
TCS Ack.
MSD Ack.
MSD Ack.
TCS Ack.
RTP
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H.245 - TunnelingTunneling 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.
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SETUP
TCS Request
• protocol identifier: version
capability Table• three items
MSD Request
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ALERTING
TCS Request
MSD Request
TCS Acknowledge
MSD Acknowledge
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FACILITY
OLC Acknowledge
Media channel
RTP Media unidirectional
OLC Request
Media control channel
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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
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ConclusionH.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)
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Thank you for your attention