+-----------------------------------------------+
        |                                               |
        | UA(Client)                         UA(Server) |
        |                                               |
        |     -------- Q4S BEGIN ------------->         |
        |     <------- Q4S BEGIN --------------         |
        |                                               |
        |     ------- Q4S BEGIN -------------->         |
        |     <------ Q4S 200 OK --------------         |
        |                                               |
        |                                               |
        +-----------------------------------------------+