[asterisk-users] SIP Codec negotiation

[Joshua Colp]

On Fri, May 11, 2018, at 10:36 AM, Steve Edwards wrote:
> On Fri, 11 May 2018, Joshua Colp wrote:
> 
> >> In the above example, even though the INVITE/SDP says they prefer gsm 
> >> over ulaw and the OK/SDP says I prefer ulaw over gsm, they can choose 
> >> to use gsm or ulaw?
> >
> > Yes.
> >
> >> Can it be asymmetrical? They send gsm and I send ulaw?
> >
> > Technically, yes. In practice it's a bit iffy - specifically because 
> > some DSPs in devices won't allow it - they require a single codec be in 
> > use for each direction.
> 
> So, Asterisk will defer it's choice of codec to match the codec it detects 
> in the incoming stream?

It depends on the channel driver and configuration. The chan_sip module always matching outgoing codec to the incoming codec. The chan_pjsip module has an option to do that (which is on by default).

-- 
Joshua Colp
Digium, Inc. | Senior Software Developer
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
Check us out at: www.digium.com & www.asterisk.org