I have a centralised call manager with remote voice gateway configured as H323. What is an acceptable round trip delay for WAN link between voice gateway and call manager? Can't seem to find in SRND.
What about for H323 signalling traffic? We are getting delay where IP phone pick up handset but external users not connect up to 3-6 seconds later.
To investigate this, you should collect the sniffer traces from call manager and h323 gw. You need to find, how long does it takes for setup to reach phone and before call manager gets the connect message. it could be delay on pstn side.
I've just been working on a network running H.323 over a total of around 600ms normal latency one way. I can tell you that this is too much! I haven't seen anyone list a recommended maximum, but since there are 3-4 proposal/ack type conversations to happen when a phone connects (even with fast start) 600ms translates easily into several seconds before audio starts.
We're switching this customer to SIP; fewer packet exchanges are involved at the 'connect' phase so it's much quicker to cut through the audio.
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This may assist as well
If you are experiencing delayed connect times over SCCP pipes to remote sites, check the Remote Device check box in the Phone Configuration window. Checking this check box tells Cisco Unified Communications Manager to allocate a buffer for the phone device when it registers and to bundle SCCP messages to the phone.