[asterisk-dev] RFC: chan_sip SDP parsing changes in behavior

[Johan Wilfer]

2012-06-01 09:20, Saúl Ibarra Corretgé skrev:
>>  
>> That could happen some day; the next step (which Kinsey Moore is working  
>> on in his spare time) is improving the SDP code to at least be able to  
>> properly respond to offers that include unsupported streams.
>>  
> That would be awesome!
>>  
>> Today, we don't have a way to respond properly to unsupported streams.  
>> If an offer includes a BFCP stream, for example, our answer will not  
>> include that stream *at all*. If that stream was in the 2nd position of  
>> a three-stream offer (audio, BFCP, video), then our answer will be  
>> really messed up because we'll have a video stream in position 2.
> I can indeed confirm that we would fail there. If the stripped stream is at the end, however, I think it can be handled.  
>>  
>> This is why I've proposed this set of changes; I'd much rather fail that  
>> session setup completely than respond with such a broken answer. The  
>> changes required to respond with a non-broken answer are significantly  
>> more invasive than what I've proposed and would certainly not be  
>> candidates for existing release branches. They *may* make it into  
>> Asterisk 11, but they aren't on the current 'committed work' list  
>> (primarily because it's rare that these problems affect calls, except  
>> when unusual endpoints are in use).
>>  
> I see. Do you have numbers in how big the impact would be? I mean, if people prepared their stacks to be gentle in what they receive but now Asterisk just rejects their offer that would be a bad thing IMHO.
>

If this is an intermediary step towards responding more compliant to SDP
offers, maybe it could be a configuration option to preserve the current
behavior until then?

compat_reject_unsupported_streams = true

To avoid pain for those who upgrade it could be false by default, but
true in the sample configuration file.
Or the releases (1.8, 10) could be shipped with a warning to consider this.

When Asterisk is more SDP compliant this option could be removed.

-- 
Johan Wilfer                 email: johan at jttech.se
JT Tech | Developer          webb: http://jttech.se