A flow control rule of Polycom MCU

Ran into a meeting bit rate related issue when conferencing with Polycom MCU.
Here is the situation:


1. My terminal(H600) attended into a multi-point meeting on Polycom MCU by using H.323 protocol.
2. The meeting bit rate was low to 1M by the setting on the meeting template.
3. All the H.225, H.245 processes seems finished, and the logical channel was opened sucessfully.
4. Then there are normal H.245 commands, like fastUpdate, roundTripDelayRequest and roundTripDelayResponse.
5. H600 sent audio and video streams to the MCU.
6. MCU did not send any stream to H600.
7. H600’s video can not be viewed on the MCU(and other participants).
8. Twenty seconds later, MCU sent a closeLogicalChannel command to H600 and re-sent TCS, re-opened the LC
9. After that, everything was just fine.

Checked the captured pcap file, found out that it could be flow control relevant.
The root cause is:
1. Meeting bit rate was 1M.
2. The total bit rate of first opened two logical channels (general Audio + general video) has exceeded 1M.
3. MCU sent a H.245 OLC(extendedVideoCapability) to H600, and after H600 replied an OLC ACK to MCU, H600 did not sent a FlowControlCommand or FlowControlIndication to MCU.

Simply put, it was caused by the limitation of the meeting band width. And the way out of this will be flowControlCommand and/or flowControlIndication after OLC and OLC ACK.

Author: Jacky Wei

I am a programmer, welcome to my blog: http://rg4.net.

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