A source transmits data packets to a receiver over a radio link. The re$-$ ceiver uses error detection to identify pack$-$ ets that have been corrupted by radio noise. When a packet is received error free, the receiver sends an acknowledgment $($ACK$)$ back to the source. When the receiver gets a packet with errors, a negative acknowl$-$ edgment $($NAK$)$ message is sent back to the source. Each time the source receives a NAK, the packet is retransmitted. We assume that each packet transmission is in$-$ dependently corrupted by errors with prob$-$ ability q$.$