[asterisk-users] No audio for 10 seconds and then comfort noise

[Dovid Bender]

David,

Are you getting any RTP from the PSTN for either leg? If not it could be
that they assume you are behind NAT and want to see where the SRC of the
RTP before they send it back. We had a few carriers that did this. The
easiest way to get around it was to play a 0.5 second audio clip to the
incoming leg. This will send RTP to the inbound carrier, causing them to
send RTP back to you which would then hit the terminating carrier, which
then sends you back RTP completing the loop. The dialplan looks
something like this.

same =>                n, Progress()
same =>                n,
Playback(/var/lib//asterisk_custom/sounds/xc,noanswer)
same =>                n, Dial(SIP/+${EXTEN}@carrier,,)






On Thu, May 19, 2022 at 12:13 AM David Cunningham <dcunningham at voisonics.com>
wrote:

> We found that the 10 seconds relates to the "rtpkeepalive =10" in our
> sip.conf. If the rtpkeepalive is reduced then the delay reduces as well. If
> rtpkeepalive is removed from sip.conf then audio never starts flowing.
>
> Does that help anyone make sense of what's happening?
>
> We have DAHDI running on the server:
>
> # asterisk -rx 'dahdi show version'
> DAHDI Version: 3.0.0 Echo Canceller:
> # asterisk -rx 'dahdi show status'
> Description                              Alarms  IRQ    bpviol CRC    Fra
> Codi Options  LBO
>
>
> On Thu, 19 May 2022 at 15:51, David Cunningham <dcunningham at voisonics.com>
> wrote:
>
>> Hello,
>>
>> We are running an Asterisk 13 server which is having a strange problem,
>> where on calls which are received from the PSTN and then forwarded out to
>> the PSTN again there is no audio for the first 10 seconds of the call. At
>> the 10 second mark audio starts flowing fine, and in a PCAP we see that it
>> starts with a few "comfort noise" packers before the real audio starts.
>>
>> It can be reproduced with a very simple extension like this:
>> exten => 4081234567, 2, Dial(SIP/6501234567 at bb.bb.bb.138)
>> where 4081234567 is the number we receive the call on, and 6501234567 is
>> the number we're forwarding it out to.
>>
>> In the Asterisk log we don't see any obvious reason for the audio to
>> start flowing at the 10 second mark. All that is logged at that time is the
>> following below.
>>
>> Would anyone have any ideas? Historically Asterisk didn't generate
>> comfort noise - has that changed in version 13?
>>
>> [May 17 20:26:24] VERBOSE[11933] res_rtp_asterisk.c: Sent Comfort Noise
>> RTP packet to aa.aa.aa.76:64280 (type 02, seq 009268, ts 000000, len 000001)
>> [May 17 20:26:24] VERBOSE[17794][C-00000027] res_rtp_asterisk.c: Got RTP
>> packet from aa.aa.aa.76:64280 (type 00, seq 000662, ts 105920, len 000160)
>> [May 17 20:26:24] DEBUG[17725][C-00000027] res_rtp_asterisk.c: Ooh,
>> format changed from none to ulaw
>> [May 17 20:26:24] DEBUG[17725][C-00000027] res_rtp_asterisk.c: Starting
>> RTCP transmission on RTP instance '0x14f4cc025998'
>> [May 17 20:26:24] VERBOSE[17725][C-00000027] res_rtp_asterisk.c: Sent RTP
>> packet to bb.bb.bb.20:35412 (type 00, seq 020934, ts 105920, len 000160)
>> [May 17 20:26:24] VERBOSE[17725][C-00000027] res_rtp_asterisk.c: Got RTP
>> packet from bb.bb.bb.20:35412 (type 00, seq 029996, ts 102760, len 000160)
>>
>> Thanks very much,
>>
>> --
>> David Cunningham, Voisonics Limited
>> http://voisonics.com/
>> USA: +1 213 221 1092
>> New Zealand: +64 (0)28 2558 3782
>>
>
>
> --
> David Cunningham, Voisonics Limited
> http://voisonics.com/
> USA: +1 213 221 1092
> New Zealand: +64 (0)28 2558 3782
> --
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