Intermittent Echo on PSTN Calls

Unanswered Question
Mar 23rd, 2007
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We have had a number of calls and entries into QRT Database complaining of Talker Echo on Calls to the PSTN.

Some of the time the same PSTN numbers appear more than once both called and calling.

Because of this I used a 7940 Phone to send out a Tone to one of the problem numbers, which happens to be a local number

(please note the problem is intermittent and not all calls to this number have Talker Echo). Also the echo doesn't always last for the duration of the call.

Equipment involved:-

7040 Phone

Call Manager 4.1.(3) SR3a.

Cisco 2851 Voice GW 12.3 using Pri on Serial0/0/0:15 (see attached for voice port config) you will notice it doesn't have any Attenuation or Gain settings

See end of attachment for the results of the "show call active voice" command whilst the Tone was being generated.

As you can see the ACOM=44 figure is high as is the ERL. I've read that the ERL=20 figure is obtained by subtracting the InSignalLevel-59 from the OutSignalLevel-15

obviously in this case the sums don't work out.

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