telemarketer
       T  ------------.         n
      ^ :              \      ----> nth step; INVITE (Also:)
      | :               \     ....> nth step; BYE (Also:)
 2(C) | : 4             3\
      | :                 \
      | V        5         V
         .................>
       A                   C
         ----------------->
  auto dialer    1      customer