Dealing with REFERs

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

• To initiate an in-dialog REFER request (with implied subscription). Use the InviteSession::refer(referTo, true /* referSub? */) API.
• To initiate an in-dialog REFER request (with no subscription). Use the InviteSession::refer(referTo, false /* referSub? */) API.
• To initiate an out of dialog REFER request (with implied subscription). Use the DialogUsageManager::makeRefer() API.
• To initiate an out of dialog REFER request (with no implied subscription). Use the DialogUsageManager::makeOutOfDialogRequest() API, and add the appropriate no-sub headers. ie:

  SharedPtr<SipMessage> refermsg = mDum.makeOutOfDialogRequest(target, userprofile, REFER, 0 /* AppDialogSet */);
  
  // Add refer To
  refermsg->header(h_ReferTo) = referTo;
  
  // Add ReferredBy header
  refermsg->header(h_ReferredBy) = mInviteSessionHandle->myAddr();
  refermsg->header(h_ReferredBy).remove(p_tag);   
  
  // Add No Sub indication
  refermsg->header(h_ReferSub).value() = "false";
  refermsg->header(h_Supporteds).push_back(Token(Symbols::NoReferSub));
  
  mDum.send(refermsg);

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
}