anchor.diff:  %% - 2xx response is received
   %% - 2xx response is provided to the TU
   %% - transaction terminates
  +%% @end
   client_ok(Transport) ->
       register(?REGNAME, self()),
   
  
positive.code:     unregister(?REGNAME),
      ok.
  
  %% Scenario tested:
  %% - client INVITE transaction is created
  %% - response is received
  
negative.code: %% - 2xx response is sent by TU
  %% - 2xx response is sent to the transport
  %% - transaction terminates
  %% @end
  server_invite_ok(Transport) ->
      register(?REGNAME, self()),
  
  