Suppose we have two network entities, A and B. B has a supply of data messagesthat will

Chapter 3, Problem P21

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Suppose we have two network entities, A and B. B has a supply of data messagesthat will be sent to A according to the following conventions. When Agets a request from the layer above to get the next data (D) message from B,A must send a request (R) message to B on the A-to-B channel. Only when Breceives an R message can it send a data (D) message back to A on the B-to-A channel. A should deliver exactly one copy of each D message to the layerabove. R messages can be lost (but not corrupted) in the A-to-B channel; Dmessages, once sent, are always delivered correctly. The delay along bothchannels is unknown and variable.Design (give an FSM description of) a protocol that incorporates the appropriatemechanisms to compensate for the loss-prone A-to-B channel andimplements message passing to the layer above at entity A, as discussedabove. Use only those mechanisms that are absolutely necessary.