title: SIP Error 481 Call/Transcation Does Not Exist when transferring
body: <p>Our phones are done through SIP and we were noticing this error appearing on our server.</p>
  
  <p>After running tests, we have determined that it only appears on inbound calls from external numbers, when we attempt to transfer that call to an internal extension. Outbound calls transferred do not produce the error.</p>
  
  <p>What is strange is that, even after showing this error, the call <strong>continues fine</strong>. Everyone can still talk, the new extension picks up the call fine. So with the actual telecommunication, there is no probem. However we do need to find out what is causing this error because it is causing havoc with our SIP call recorder.</p>
  
  <p>Here is the wireshark trace we are getting on an independent call. At time 29 is when the internal transfer is made.</p>
  
  <p><img src="https://i.stack.imgur.com/GyxLQ.png" alt="Wireshark screenshot with numbers blacked"></p>
  
  <p>I understand that this error is caused by a UAS receiving a SIP packet for  call of which it is not aware. However thati s about where my knowledge ends. In the first instance of the error, I am curious as to whether the source being the external gateway IP means that is a problem at the other end? This can't be the case as it happens on calls from anyone.</p>
  
  <p>Thanks in advance!</p>
  
  <p><strong>Packet headers</strong></p>
  
  <p><a href="http://oi61.tinypic.com/2i0b57o.jpg" rel="nofollow noreferrer">545</a> <a href="http://oi62.tinypic.com/so5pav.jpg" rel="nofollow noreferrer">1248</a> <a href="http://oi61.tinypic.com/28u2o11.jpg" rel="nofollow noreferrer">3945</a> <a href="http://i61.tinypic.com/2eob95x.png" rel="nofollow noreferrer">3950</a></p>