Hi,

I was able to use Unsniff to validate that the incoming 20 byte payloads of 
audio from the downstream IAX2 trunk was definitely G.729a whilst Asterisk 
16.13.0 transcodes to G.711a unnecessarily. Media is confirmed as having been 
negotiated as g729 on all four streams. Nuance with this call is that it's from 
a WebRTC client which doesn't transmit any audio, could this be influencing 
Asterisk?

I couldn't post the asterisk debug in the mailing list, perhaps we could 
consider increasing maximum messages sizes from 40 KiB in 2020? I subsequently 
opened a case in JIRA instead 
(https://issues.asterisk.org/jira/browse/ASTERISK-29096).


In the below +27888888888 (chan_sip) calls 0100000000 (chan_iax), negotiates 
g729 on both legs of the bridged call, exclusively receives g729 media from 
0100000000 (chan_iax) but then transmits g711a media to +27888888888 (chan_sip).

Herewith the scrubbed and reduced dialogues, full details are available in the 
JIRA case:
[2020-09-19 23:42:19] VERBOSE[2637] chan_sip.c:
<--- SIP read from UDP:41.11.11.12:5060 --->
INVITE sip:0100000000@52.22.22.22:5160 SIP/2.0
Record-Route: <sip:41.11.11.12;lr;ftag=as40fe2614>
Via: SIP/2.0/UDP 41.11.11.12:5060;branch=z9hG4bK4df7.5bc77035.0
Via: SIP/2.0/UDP 
41.11.11.11:5070;received=41.11.11.11;branch=z9hG4bK0cb77ea3;rport=5070
From: "+27888888888" <sip:+27888888888@41.11.11.11:5070>;tag=as40fe2614
To: <sip:0100000000@52.22.22.22:5160>
Contact: <sip:+27888888888@41.11.11.11:5070>
Call-ID: 
7030be5a09d89a9543234da051897a49@41.11.11.11<mailto:7030be5a09d89a9543234da051897a49@41.11.11.11>
CSeq: 102 INVITE
User-Agent: PortaOne
Max-Forwards: 69
Date: Sat, 19 Sep 2020 21:42:19 GMT
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
Supported: replaces
X-LOCATION:
X-StartID: SDvb9r601-d482cc2b5e0b32417957ea02aaade464-a04aba0
Content-Type: application/sdp
Content-Length: 283

v=0
o=root 6009 6009 IN IP4 41.11.11.11
s=session
c=IN IP4 41.11.11.11
t=0 0
m=audio 13918 RTP/AVP 18 8 101
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:8 PCMA/8000
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=silenceSupp:off - - - -
a=ptime:20
a=sendrecv
<------------->
<snip>
[2020-09-19 23:42:19] VERBOSE[2637][C-00021a1f] chan_sip.c: Capabilities: us - 
(g722|alaw|g729), peer - audio=(alaw|g729)/video=(nothing)/text=(nothing), 
combined - (alaw|g729)
<snip>
[2020-09-19 23:42:19] VERBOSE[15153][C-00021a1f] pbx.c: Executing 
[0100000000@incoming:1] Set("SIP/Upstream-00021a0d", "1?SIP_CODEC=g729") in new 
stack
[2020-09-19 23:42:19] VERBOSE[15153][C-00021a1f] pbx.c: Executing 
[0100000000@incoming:2] NoOp("SIP/Upstream-00021a0d", "SIP Call ID: 
7030be5a09d89a9543234da051897a49@41.11.11.11<mailto:7030be5a09d89a9543234da051897a49@41.11.11.11>")
 in new stack
[2020-09-19 23:42:19] VERBOSE[15153][C-00021a1f] pbx.c: Executing 
[0100000000@incoming:3] Dial("SIP/Upstream-00021a0d", 
"iax2/Downstream/0100000000") in new stack
[2020-09-19 23:42:19] VERBOSE[15153][C-00021a1f] app_dial.c: Called 
iax2/Downstream/0100000000
[2020-09-19 23:42:20] VERBOSE[2602][C-00021a1f] chan_iax2.c: Call accepted by 
196.43.209.105:4569 (format g729)
[2020-09-19 23:42:20] VERBOSE[2602][C-00021a1f] chan_iax2.c: Format for call is 
(g729)
<snip>
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] app_dial.c: 
IAX2/Downstream-26055 answered SIP/Upstream-00021a0d
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] chan_sip.c: Set codec to 
'g729' for this call because of ${SIP_CODEC*} variable
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] chan_sip.c: Set codec to 
'g729' for this call because of ${SIP_CODEC*} variable
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] chan_sip.c: Audio is at 17678
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] chan_sip.c: Adding codec g729 
to SDP
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] chan_sip.c: Adding non-codec 
0x1 (telephone-event) to SDP
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] chan_sip.c:
<--- Reliably Transmitting (NAT) to 41.11.11.12:5060 --->
SIP/2.0 200 OK
Via: SIP/2.0/UDP 
41.11.11.12:5060;branch=z9hG4bK4df7.5bc77035.0;received=41.11.11.12;rport=5060
Via: SIP/2.0/UDP 
41.11.11.11:5070;received=41.11.11.11;branch=z9hG4bK0cb77ea3;rport=5070
Record-Route: <sip:41.11.11.12;lr;ftag=as40fe2614>
From: "+27888888888" <sip:+27888888888@41.11.11.11:5070>;tag=as40fe2614
To: <sip:0100000000@52.22.22.22:5160>;tag=as11a1cd82
Call-ID: 
7030be5a09d89a9543234da051897a49@41.11.11.11<mailto:7030be5a09d89a9543234da051897a49@41.11.11.11>
CSeq: 102 INVITE
Server: Asterisk PBX 16.13.0
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY, INFO, 
PUBLISH, MESSAGE
Supported: replaces, timer
Contact: <sip:0100000000@52.22.22.22:5160>
Content-Type: application/sdp
Content-Length: 259

v=0
o=root 430525994 430525994 IN IP4 52.22.22.22
s=Asterisk PBX 16.13.0
c=IN IP4 52.22.22.22
t=0 0
m=audio 17678 RTP/AVP 18 101
a=rtpmap:18 G729/8000
a=fmtp:18 annexb=no
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=maxptime:230
a=sendrecv

<------------>
[2020-09-19 23:42:22] VERBOSE[15154][C-00021a1f] bridge_channel.c: Channel 
IAX2/Downstream-26055 joined 'simple_bridge' basic-bridge 
<0d377050-bca3-4db8-81e0-f677e37c24e9>
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] bridge_channel.c: Channel 
SIP/Upstream-00021a0d joined 'simple_bridge' basic-bridge 
<0d377050-bca3-4db8-81e0-f677e37c24e9>
[2020-09-19 23:42:22] VERBOSE[2637] chan_sip.c:
<snip>
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] res_rtp_asterisk.c: Sent RTP 
packet to      41.11.11.11:13918 (type 8, seq 020640, ts 000160, len 000160)
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] res_rtp_asterisk.c: Sent RTP 
packet to      41.11.11.11:13918 (type 8, seq 020641, ts 000320, len 000160)
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] res_rtp_asterisk.c: Sent RTP 
packet to      41.11.11.11:13918 (type 8, seq 020642, ts 000480, len 000160)
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] res_rtp_asterisk.c: Sent RTP 
packet to      41.11.11.11:13918 (type 8, seq 020643, ts 000640, len 000160)
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] res_rtp_asterisk.c: Sent RTP 
packet to      41.11.11.11:13918 (type 8, seq 020644, ts 000800, len 000160)
[2020-09-19 23:42:22] VERBOSE[15153][C-00021a1f] res_rtp_asterisk.c: Sent RTP 
packet to      41.11.11.11:13918 (type 8, seq 020645, ts 000960, len 000160)


Regards
David Herselman
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