A Selective Repeat ARQ operates as the link layer protocol of a satellite transmission channel….

A Selective Repeat ARQ operates as the link layer protocol of a satellite transmission channel. The satellite channel alternates between three states: state 1, where the bit-error probability is  The steady state probabilities that the channel is in each of the states are for states 1, 2 and 3, respectively. The transmission rate at the link layer is constant and equal to Rb = 1 Mbit/s, whereas the size of the PDU headers is 100 bits. Also, assume that the channel state never changes during the transmission of link layer PDUs.

a) Find the average transmission efficiency, η, expressed in bit/s, of SR-ARQ when PDUs have a constant size of 500 bytes, including data and header fields.

b) Calculate the average transmission efficiency, η, expressed in bit/s, of a modified SR-ARQ scheme where the PDU size is optimally adapted as a function of the channel state.