|Request from TU                           
                              |send request                               
          Timer E             V                                           
          send request  +-----------+                                     
              +---------|           |-------------------+                 
              |         |  Trying   |  Timer F          |                 
              +-------->|           |  or Transport Err.|                 
                        +-----------+  inform TU        |                 
           200-699         |  |                         |                 
           resp. to TU     |  |1xx                      |                 
           +---------------+  |resp. to TU              |                 
           |                  |                         |                 
           |   Timer E        V       Timer F           |                 
           |   send req +-----------+ or Transport Err. |                 
           |  +---------|           | inform TU         |                 
           |  |         |Proceeding |------------------>|                 
           |  +-------->|           |-----+             |                 
           |            +-----------+     |1xx          |                 
           |              |      ^        |resp to TU   |                 
           | 200-699      |      +--------+             |                 
           | resp. to TU  |                             |                 
           |              |                             |                 
           |              V                             |                 
           |            +-----------+                   |                 
           |            |           |                   |                 
           |            | Completed |                   |                 
           |            |           |                   |                 
           |            +-----------+                   |                 
           |              ^   |                         |                 
           |              |   | Timer K                 |                 
           +--------------+   | -                       |                 
                              |                         |                 
                              V                         |                 
        NOTE:           +-----------+                   |                 
                        |           |                   |                 
    transitions         | Terminated|<------------------+                 
    labeled with        |           |                                     
    the event           +-----------+                                     
    over the action                                                       
    to take