How does this call flow?

Can any one explain me how does this below call flow?

http://lh4.ggpht.com/_cBBGhuN8esk/SZ6wqgef_fI/AAAAAAAAACY/XjOQAZeTjDE/s576/CTI%20T%20Server%20Call.jpg

I have some idea on the above call flow. But still i need to know how does the above call flow exactly ?

Please help me