+------+                              +------+
|Client|                              |Server|
+------+                              +------+
   |======QUOTATION (Requested CPD)=====>|
   |<============PROCESSING==============|
   |<========OFFER (Offered CPD)=========|
   |=============PROCESSING=============>|
   |=======ACCEPT (Accepted CPD)========>|
   |<=======ACK (Accepted CPD)===========|
   |                                     |