Resequencing Delay and Buffer Occupancy Under the Selective-Repeat ARQ

Abstract

Consider a communication network that regulates retransmissions of erroneous packets by a selective-repeat (SR) automatic repeat request (ARQ) protocol. Packets are assigned consecutive integers, and the transmitter continuously transmits them in order until a negative acknowledgment or a time-out is observed. The receiver, upon receipt of a packet, checks for errors and returns positive/negative acknowledgment (ACK/NACK) accordingly. Only packets for which either NACK or time-out have been observed are retransmitted. Under SR ARQ, the receiver accepts packets that are out of order and must store them temporarily if it has to deliver them in sequence. The resequencing buffer requirements and the resulting packet delay constitute major factors in overall system considerations. We derive the distributions of the buffer occupancy and the resequencing delay at the receiver under a heavy traffic situation. This enables the network designer to determine how much buffer capacity at the receiver will guarantee certain specified performance measures. © 1989 IEEE