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Long Delays in audio


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I have been noticing that certain situations cause a long delay in the audio between two parties, and I was wondering what may cause this. It seems that the more legs that are involved in a call, the longer the delay gets. For example, if an extension calls an extension on another PBX that is directly networked to it, then the call is usually fine, however if it forks to the cell phone, then there is a couple second delay. However however if that same extension calls the cell directly (utilizing the same PSTN gateway, just not forking through the second PBX, then there is no noticeable delay) Since it does not happen with every call, I am wondering if adaptive jitter buffers are being additive. Most all of the links in this example have a fairly consistent latency of ~ 50ms, however I have seen occasions where the latency might jump to 120ms for one instant within the total duration of the call. Does this cause the jitter buffer to increase, and never decrease again for the duration of the call? We are not having any noticeable audio issues such as cutting out, dropping, or 1 way audio. Just looking for some input as to how I can fix the long delay that does not happen all the time.

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More than a second delay cannot be explained by having the PBX in the media path. The speed of light (and information) is 186.000 miles per second). That would make it possible to send the call around the world a couple of times. There must be something else going on.


Sometimes the problem is that the bandwidth gets to the edge, and the packets somehow make it, but very slow. The other situation that we have seen is that packets were run over a cellular data network, where the carrier seems to slow the packet down (to make it unusable for VoIP I would guess).

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