The protocol provided by the delivery service is depicted in Fig. 1.2. The protocol starts upon a request for transporting an object of a given size to a given location. This might not be possible, in which case the applicant is notified, and the protocol terminates failing. Otherwise, a cost and delivery time are computed and signaled to the applicant; the protocol suspends for either a positive or negative acknowledgment, terminating (with success or failure respectively) upon its reception.