anchor.diff:        "c=IN IP4 0.0.0.0\r\n",
         "t=0 0\r\n",
         "m=audio ", Port/binary, " RTP/AVP 112 113\r\n",
  -      "a=rtpmap:112 L16/48000/2\r\n",
  -      "a=rtpmap:113 DAT12/32000/4\r\n",
  -      "a=fmtp:113 contents:DV L/R/C/WO\r\n">>.
  -
  +      "a=rtpmap:112 speex/32000/1\r\n",
  +      "a=fmtp:112 vbr=on">>.
  
positive.code: 
      CSeq = sip_message:header_top_value(cseq, Response),
      ACK2 = sip_message:replace_top_header(cseq, CSeq#sip_hdr_cseq{method = 'ACK'}, ACK),
      ACK3 = sip_message:append_header('content-type', <<"application/sdp">>, ACK2),
      ACK4 = ACK3#sip_request{body = sdp()},
      sip_ua:send_request(ACK4),
  
      {noreply, State};
  handle_response(#sip_request{method = 'INVITE'}, #sip_response{status = Status} = Response, RequestId, State) when Status >= 300 ->
  
negative.code:     % Request will be cancelled automatically after 5 seconds
      Request4 = sip_message:append_header(expires, 5, Request3),
  
      % put session in INVITE
      Request5 = sip_message:append_header('content-type', <<"application/sdp">>, Request4),
      Request6 = Request5#sip_request{body = sdp()},
  
      % Call
      io:format("HANG: Calling to ~s~n", [to(Request6)]),
      {ok, _RequestId} = sip_ua:send_request(Request6),
  
      {reply, ok, State};
  
  