401 Notes

On sip trace You need to go through to the end of the 2xx, 3xx, 4xx, 5xx or 6xx response, except that if you get 401, you need to go through to the end of the result of the repeat of the INVITE with authentication.



401 is not an error. It is normal stage in the registration process. If the registering device doesn't proceed beyond the 401, it means it does not know how to authenticate itself.

21.4.2 401 Unauthorized

   The request requires user authentication.  This response is issued by
   UASs and registrars, while 407 (Proxy Authentication Required) is
   used by proxy servers.

When a UAS receives a request from a UAC, the UAS MAY authenticate
   the originator before the request is processed.  If no credentials
   (in the Authorization header field) are provided in the request, the
   UAS can challenge the originator to provide credentials by rejecting
   the request with a 401 (Unauthorized) status code.