+----------+      +-----------+                   +-----------+          
 |          |      |           |                   |           |          
 |          |      |           |                   |           |          
 |   UA     |      |   LIS     |                   |   proxy   |          
 |          |      |           |                   |           |          
 +-----+----+      +-----+-----+                   +-----+-----+          
       |                 |                               |                
       |                 |                               |                
       |SUBSCRIBE        |                               |                
       |---------------->|                               |                
       |Event:locationref|                               |                
       |                 |                               |                
       |                 |                               |                
       |NOTIFY           |                               |                
       |<----------------|                               |                
       |sip:xu56@lis     |                               |                
       |                 |                               |                
       |                 |                               |                
       |INVITE           |                               |                
       |-----------------+------------------------------>+---------       
       |Geolocation:     |                               |                
       |xu56@lis         |                               |                
       |                 |   SUBSCRIBE xu56@lis          |                
       |                 |<------------------------------|                
       |                 |   Event: presence             |                
       |                 |                               |                
       |                 |   NOTIFY sip:proxy.com        |                
       |                 |------------------------------>|                
       |                 |   PIDF-LO                     |                
       |                 |                               |