Once in a while, it seems that incoming calls have a delay (or silence) for a while before the far end can hear and start a conversation. This delay varies from 2 secs to 8 secs. I suspect it is a Call Manager problem but I'm not sure.
Has anyone experienced this problem before? Any suggestions are welcome.
With H.323 based gateways it is possible to see this type of behaviour on a call inbound thru the gateway into the CallManager system.
It occurs when the delay through the network between the gateway and CallManager is extremely high for the H.323 control traffic. If you are experiencing an 8 s delay, then this suggests the round trip time between the gateway and CallManager is about 1 second.
Note: This is only experienced for
i) networks with high delay.
ii) is only experienced on inbound calls
iii) is worse for H.323 gateways than MGCP gateways. Currently MGCP is more efficient at setting the call up ( less packets to send).
At the moment, to avoid the situation,
i) manage the control traffic with QOS features like LLQ.
ii) manage the delay between the callmanager and gateway ( if possible)
Note that this is caused by the interaction of H.323 as it sends many packets to set the stream up.
The information you supplied was very enightening. However, I am not using an H.323 gateway. The voice system is totally configured with MGCP. I'll try to look into the possible delay between the Call Manager and Gateway and make sure I have no such issues. The incoming calls in question are from the PSTN, which I guess may have appreciable delay from time to time.
Any protocol, even MGCP can have this issue. From memory, takes about 6 packets to get the stream setup with MGCP, and about 17 for H.323. So the delay of the network can have an impact, less so with MGCP than H.323.
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