+
+After the correct challenge replies are recieved, both ends have proved
+their identity. Further information is exchanged.
+
+client ACK 655 123 0
+ | | +-> options
+ | +----> estimated weight
+ +--------> listening port of client
+
+server ACK 655 321 0
+ | | +-> options
+ | +----> estimated weight
+ +--------> listening port of server