[reSIProcate] Documenting how-to handle 439 outbound not supported case

[Aron Rosenberg <arosenberg@xxxxxxxxxxxx>]

All,

I was doing some interop testing with a pstn provider and they have a setup which results in 439 (first hop doesn't support outbound). My guess is their SBC is stupid, but their registrar is smart, so I was going to implement the logic in RFC 5626 4.2.1 in our UAC:

 If the registering UA receives a 439 (First Hop Lacks Outbound
   Support) response to a REGISTER request, it MAY re-attempt
   registration without using the outbound mechanism (subject to local
   policy at the client).

To support this with the current outbound implementation, upon receiving the 439, you must issue a new makeRegistration with the outbound pieces of the new UserProfile disabled. Simply turning off just the features in the existing UserProfile attached to the Handle and attempting refresh doesn't work.

 void onFailure(ClientRegistrationHandle crh, const SipMessage& msg)

 {

    resip::SharedPtr<UserProfile> up(crh->getUserProfile());

    if(msg.header(h_StatusLine).responseCode() == 439) // 439 means non outbound supported path to Registrar. Retry without outbound support.

    {

        up->setInstanceId(Data());

        up->setRegId(0);

        up->clientOutboundEnabled() = false;

	resip::SharedPtr<resip::SipMessage> reg = dum->makeRegistration(....); // Pass in up, the modified UserProfile

	dum->send(reg);

        return;

    }

    ....

 }

I added this documentation to https://www.resiprocate.org/DUM_Client_Outbound_Support

Aron Rosenberg

Sr. Director, Engineering

Logitech Inc. (SightSpeed Group)