Disabling Packet Loss Concealment features of IAD 2400.

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Jan 22nd, 2008
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Hello,

I am looking for a way to disable the Concealment features of the DSP in the IAD. I haven't been able to find a command to do this. Is there a hidden command or is this just not possible?


I am running 12.4(17) on an IAD2431-16FXS.

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pcameron Tue, 01/22/2008 - 14:13
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You can't - this function is built into the codec and cannot be changed.


Why would you want to anyway ?


lantago Tue, 01/22/2008 - 14:45
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Thanks for the reply.


We have noticed that on non Cisco equipment, there are times that PLC causes more problems that it solves, but that it's most likely due to poor implementation of the DSP / decoder.


The problem we are facing has to do with DTMF. We have a remote device that takes 20 to 30 ms to detect DTMF.. so 20 to 30 ms of DTMF is included inband in the audio stream. Once the remote device does detect DTMF, it stops sending the audio stream and sends an out-of-band notification... that isn't sent until the end of the event.


This causes a problem with equipment on FXS lines, as it now "heard" 2 DTMF events. The inital DTMF event is the 20 to 30 ms of audio coming through PLUS the PLC of the IAD of 20 ms to cover for the lost packet. ITU Q.27 spec states that after 40 ms DTMF has to be detected and recgonized.


The second DTMF event that is hear is the out-of-band message coming into the IAD and then being generated.


We wanted to test to see if the problem existed with we turned off the PLC of the device.

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