[Freeswitch-users] Receiving audio despite SDP with a=sendonly

[Larry Hemenway]

It looks like FreeSWITCH does not support one-way audio at all. We have a
strong need for this functionality if we choose to use FreeSWITCH. If I
were to investigate and implement this, is it something that the community
would be interested in? I'm a bit worried about diving into this because if
FreeSWITCH honors the sdp direction it could potentially break some legacy
applications that rely on current functionality.

Also, any tips on where to start would be appreciated.

More info on my investigation:

I got a little smarter in how I search the mailing list and came across
this, so it sounds like this is not supported functionality.

http://freeswitch-users.2379917.n2.nabble.com/sendonly-attribute-ignored-td5933886.html

I also ran some more experiments. The reinvite with a=sendonly results in a
hold event, so I verified audio is not passed in either direction despite
the SDP direction attribute.

I'm currently doing these experiments with a conference. We would like to
use it as a sort of intercom function, but our security group is strongly
discouraging us from making a product that sends audio to all the endpoints
even if its silence, so the conference relate API, from their perspective,
isn't a solution.

Larry



On Wed, Feb 21, 2018 at 5:09 PM, Larry Hemenway <larry.hemenway at gmail.com>
wrote:

> Hello,
>
> Is there a way to establish a call with one-way audio on a call from the
> start?
>
> I'm currently sending a request with the following SDP - (note a=sendonly):
>
> v=0
> o=Larry 2890844526 2890844526 IN IP4 127.0.0.1
> s= My Session
> c=IN IP4 172.22.112.1
> t=0 0
> m=audio 49170 RTP/AVP 0 8
> a=sendonly
> a=rtpmap:0 PCMU/8000
> a=rtpmap:8 PCMA/8000
>
> FreeSWITCH is sending back the right response (note the a=recvonly):
>
> v=0
> o=FreeSWITCH 1519171720 1519171721 IN IP4 172.17.0.2
> s=FreeSWITCH
> c=IN IP4 172.17.0.2
> t=0 0
> m=audio 21768 RTP/AVP 0 101
> a=rtpmap:0 PCMU/8000
> a=rtpmap:101 telephone-event/8000
> a=fmtp:101 0-16
> a=recvonly
> a=ptime:20
>
> But I'm still receiving audio from FreeSWITCH. It is only after I
> resend the SDP via a reinvite that the audio stops being sent from
> FreeSWITCH.
>
> Larry
>
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