Dealing with REFERs

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Setup Required in order to Use REFER

  • To add support for the REFER method
mProfile->addSupportedMethod(REFER); 
  • To add support for receiving NOTIFY's with message/sipfrag bodies
mProfile->addSupportedMimeType(NOTIFY, Mime("message", "sipfrag"));  
  • To add support for REFER with replaces header
mProfile->addSupportedOptionTag(Token(Symbols::Replaces));
  • To add support for REFER with no implied subscription
mProfile->addSupportedOptionTag(Token(Symbols::NoReferSub));
  • To add support for reception of out-of-dialog REFERs
mDum.addOutOfDialogHandler(REFER, mHandler);
  • To add Support for the implied server subscription when receiving a REFER
mDum.addServerSubscriptionHandler("refer", mHandler);
  • To add Support for the implied client subscription when sending a REFER
mDum.addClientSubscriptionHandler("refer", mHandler);


Initiating REFER Requests

Use the InviteSession::refer(referTo) API - this will cause a REFER message to be sent to the other party.


Handling REFER Requests

If an application wishes to process the REFER request it should use the dum->makeInviteSessionFromRefer API.

Sample Code:

void onRefer(InviteSessionHandle is, ServerSubscriptionHandle ss, const SipMessage& msg)
{
   ss->send(ss->accept(202));  // accept refer request
   SdpContents sdpOffer;
   ...  // build sdpOffer
   dum->send(dum->makeInviteSessionFromRefer(msg, ss, sdpOffer);  // send new INVITE
}


Handling REFER with Replaces Requests

Sending REFER with Replaces

Use the InviteSession::refer(referTo, sessionToReplace) API - this will cause a REFER message to be sent to the other party that contains a Replaces header specifying the session to replace.

Receiving REFER with Replaces

For an application standpoint, this is handled in the exact same manner as receiving a REFER request without a Replaces header. If an application wishes to process the REFER request it should use the dum->makeInviteSessionFromRefer API.

Sample Code:

void onRefer(InviteSessionHandle is, ServerSubscriptionHandle ss, const SipMessage& msg)
{
   ss->send(ss->accept(202));  // accept refer request
   SdpContents sdpOffer;
   ...  // build sdpOffer
   dum->send(dum->makeInviteSessionFromRefer(msg, ss, sdpOffer);  // send new INVITE
} 

Receiving INVITE with Replaces

When you receive an INVITE request (via the onNewSession callback) you may wish to see if a Replace header is present, in order for this new INVITE session to "take over" an existing session. In order to accomplish this you can use a convience function on the DialogUsageManager called findInviteSession which takes a Replaces header as an argument.

Sample Code:

void onNewSession(ServerInviteSession sis, InviteSession::OfferAnswerType oat, const SipMessage& msg)
{
   if (msg->exists(h_Replaces))
   {
      pair<InviteSessionHandle, int> presult;
      presult = dum->findInviteSession(msg->header(h_Replaces));
      if (presult != InviteSessionHandle::NotValid())
      {
          ... // Do stuff in app to swap contexts
          Presult.first->end(); // end original session
      }
   }
   ...continue with app specific stuff
}