All,
I just found this after some further extensive digging around - this explains whatactually happens and that my assumption was completely wrong.
- The ICT is handling the call control between clusters only
- SCCP between UCM's and phones,
- RTP stream is between the phones after the UCM's exchange the information about IP addresses and Ports used.
If anyone else was confused, hope that helps, sorry for what might have seemed a very basic and incorrect assumption
Steve
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H.323 also provides a RAS (Registration, Admission and Status) channel. It uses this channel for auto-discovery of a Gatekeeper. The Gatekeeper is a device that provides for call admission control. An example of a Call Manager H.323 call flow is listed below with details for each step. The StationD and StationInit messages are actual SCCP message sent between the Call Manager and the IP phone. Station D messages are from the Call Manager to the IP phone. StationInit messages are from the IP phone to the Call Manager. In this example, IP phone 3000 in Call Manager cluster 1 is calling IP phone 4000 in cluster 2. Intercluster trunks are used to link the clusters. This is one area where the H.323 communication takes place. In this example, you see a trace file from the originating Call Manager in cluster 1. Cluster 2 will also have a corresponding trace file for its portion of the call.
16:06:12.921 CCM|StationInit - InboundStim - OffHookMessageID
tcpHandle=0x1c64310
StationInit messages are sent from the IP phone to the Call Manager. This message indicates that the IP phone has gone off-hook. A TCP handle is assigned to the call that can be used as a reference throughout the life of the call.
16:06:13.953 CCM|Out Message -- H225ConnectMsg -- Protocol= H225Protocol
Initiates the H225 connection request to cluster 2
16:06:13.953 CCM|Ie - H225UserUserIe IEData= 7E 00 37 05 02 C0 06
The IE (information element) contains detailed information about the call. This is passed from cluster 2 to this cluster
16:06:13.953 CCM|StationD - stationOutputCallInfo
CallingPartyName=, CallingParty=3000, CalledPartyName=4000,
CalledParty=4000, tcpHandle=0x1c64310
Passed to local IP phone from Call Manager to indicate calling and called party info.
16:06:14.015 CCM|H245Interface(2) OLC indication chan number = 2
Opens a logical channel for transport of audiovisual and data information
16:06:14.015 CCM|StationD - stationOutputOpenReceiveChannel
tcpHandle=0x1c64310 myIP: e74610ac (172.16.70.231)
Call Manager tells the local IP phone to open a receive channel to its IP address.
16:06:14.015 CCM|StationD - ConferenceID: 0 msecPacketSize: 20
compressionType:(4)Media_Payload_G711Ulaw64k
Packet size and compression type is communicated to the local IP phone.
16:06:14.062 CCM|StationInit - InboundStim -
StationOpenReceiveChannelAckID tcpHandle=0x1c64310, Status=0,
IpAddr=0xe74610ac, Port=20444, PartyID=2
Local IP phone acknowledges receipt of open receive channel request. It also tells the phone in cluster 2 its IP address and RTP port.
16:06:14.062 CCM|H245Interface(2) paths established ip =
e74610ac, port = 20444
One way RTP path is established from cluster 2 to cluster 1.
16:06:14.187 CCM|H245Interface(2) OLC outgoing confirm ip =
fc4610ac, port = 29626
Cluster 1 sends open logical channel confirmation to cluster 2's IP address and RTP port number.
16:06:14.187 CCM|StationD - stationOutputStartMediaTransmission tcpHandle=0x1c64310 myIP: e74610ac (172.16.70.231)
Call Manager tells the local IP phone to begin RTP stream to the IP phone in cluster 2. This is a direct stream. It does not flow through the Call Manager.
16:06:14.187 CCM|StationD - RemoteIpAddr: fc4610ac
(172.16.70.252) RemoteRtpPortNumber: 29626 msecPacketSize: 20
compressionType:(4)Media_Payload_G711Ulaw64k
Call Manager tells the local IP phone about the IP address, RTP port and packet size of cluster 2's phone.
16:06:16.515 CCM|StationD - stationOutputCloseReceiveChannel
tcpHandle=0x1c64310 myIP: e74610ac (172.16.70.231)
Call Manager tells the local IP phone to close the receive channel.
16:06:16.515 CCM|StationD - stationOutputStopMediaTransmission
tcpHandle=0x1c64310 myIP: e74610ac (172.16.70.231)
Call Manager tells the local IP phone to stop media transmission to cluster 2's IP phone.
16:06:16.531 CCM|In Message -- H225ReleaseCompleteMsg --
Protocol=H225Protocol
Call Manager 1 receives an H225 message from cluster 2 indicating that the resource release was complete.
16:06:16.531 CCM|Ie - Q931CauseIe -- IEData= 08 02 80 90
16:06:16.531 CCM|Ie - H225UserUserIe -- IEData= 7E 00 1D 05 05 80 06
H225 and Q931 Information Elements that identify why the call was disconnected. Call Manager has tools that can decode these messages.
16:06:16.734 CCM|StationInit - InboundStim - OnHookMessageID
tcpHandle=0x1c64310
The local IP phone hangs up.
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