[asterisk-dev] asterisk 16 / pjsip: SDP handling on outbound calls - unnecessary transcoding

[Michael Maier]

On 22.06.19 at 23:59 Joshua C. Colp wrote:
> On Sat, Jun 22, 2019, at 4:40 PM, Michael Maier wrote:
>> Hello!
>>
>> On outbound calls, the codecs for the subsequent INVITE to the ISP are 
>> derived from the codecs defined for the trunk and from the received 
>> INVITE from the local device.
>>
>> The codecs presented by the ISP in 200 OK seem to be ignored 
>> unfortunately later on.
>>
>> E.g.:
>> direct_media				disabled
>> Local endpoint definition: 		g722, alaw, ulaw
>> Trunk definition: 			g722, alaw, ulaw
>>
>> Outbound call:
>> Initial INVITE from local endpoint: 	g722, alaw, ulaw, g726
>>
>> Subsequent INVITE to ISP: 		g722, alaw, ulaw (the codecs are derived 
>> from the initial INVITE and the codecs defined for the trunk)
>> Response from ISP: 200 OK: 		alaw
>>
>> 200 OK to local endpoint: 		g722, alaw, ulaw (based on initial INVITE 
>> and local endpoint definition - the 200 OK from the ISP is ignored)
>>
>> => asterisk has to transcode between g722 <-> alaw
>>
>>
>> Is there any chance to get the codec information of the ISP during 
>> building the 200 OK for the local endpoint in 
>> handle_negotiated_sdp_session_media() or maybe somewhere else? Or did I 
>> miss something else? I want to remove g722 in 200 OK to
>> local endpoint.
> 
> There's nothing built in explicitly to do this and it's not something that has really been scoped out. A few people have wanted such functionality, but it hasn't been implemented. You can't really reach across and get the information - it has to be communicated back probably through using a frame.

That's a pity. Especially because it's working as expected on inbound calls.

What do you exactly mean by "using a frame"?


BTW, while analyzing, I found a potentially unnecessary variable in set_caps (see patch), which never seems to be used. I removed it without any side effects yet.


Thanks
Michael
-------------- next part --------------
A non-text attachment was scrubbed...
Name: sdp.patch
Type: text/x-patch
Size: 669 bytes
Desc: not available
URL: <http://lists.digium.com/pipermail/asterisk-dev/attachments/20190623/da87ff22/attachment.bin>