[asterisk-users] Is 100 trying mandatory? Can asterisk answer with 180 without prior 100 trying?

[Joshua Colp]

On Mon, Mar 19, 2018, at 12:53 PM, Benoit Panizzon wrote:
> Hey List
> 
> I sometimes use our asterisk server to do some debugging or other PBX
> and SBC.
> 
> Now we have a case where a PBX is replying an incomming invite with 180
> ringing immediately. It looks like the SBC does not accept this.
> 
> According to my understanding of the RFC 3261 any provisional (aka
> 1XX) reply should be good enough to make the sender stop re-sending
> invites and accept this as a reply from the destination.
> 
> So 100 trying would be option and a reply could also be directly 180
> ringing.

Indeed. In practice though you want to stop the retransmission immediately and you usually don't know of the appropriate response yet so 100 is sent.

> 
> So maybe some RFC specialist could tell me how this is exactly supposed
> to work of if I maybe missed some other RFC more clear about that topic.
> 
> To try to reproduce the problem with our SBC, is there a way to tell
> the asterisk, preferably PJSIP, to directly answer with 180 ringing
> without prior 100 trying?

The PJSIP channel driver has no option or ability to do this. I do not recall if chan_sip does.

-- 
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