miroslav voznak, lecture on h.3231 miroslav vozňák vŠb - technical university of ostrava...

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

mailto:[email protected]

http://homel.vsb.cz/~voz29

http://homel.vsb.cz/~voz29


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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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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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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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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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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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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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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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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

TCS Acknowledge

MSD Acknowledge


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FACILITY

OLC Request

forward logicalchannel


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FACILITY

OLC Acknowledge

Media channel

RTP Media unidirectional

OLC Request

Media control channel


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FACILITY

OLC Acknowledge

Media channel

RTP Media bidirectional


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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

[email protected]

mailto:[email protected]

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