bob                    
                                                 +----+                   
                                                 | UA |                   
                                                 |    |                   
                                                 +----+                   
                                                    |                     
                                                    |3)INVITE             
                                                    |   carol@chicago.com 
           chicago.com        +--------+            V                     
           +---------+ 2)Store|Location|4)Query +-----+                   
           |Registrar|=======>| Service|<=======|Proxy|sip.chicago.com    
           +---------+        +--------+=======>+-----+                   
                 A                      5)Resp      |                     
                 |                                  |                     
                 |                                  |                     
       1)REGISTER|                                  |                     
                 |                                  |                     
              +----+                                |                     
              | UA |<-------------------------------+                     
     cube2214a|    |                            6)INVITE                  
              +----+                    carol@cube2214a.chicago.com       
               carol