The stop and wait protocol Original ARQ protocol Sender transmits one packet at a time and waits for an ACK Receiver ACKs packets Sender retransmits packet after a timeout PKT-0 PKT-1 PKT-2 PKT-2 ACK-0 ACK-1 ACK-2 Packet numbering Sender numbers packets with sequence numbers (sN) Receiver uses request numbers(Rn) to ACK packets RN=jis the same as an ACK for packet j-1 ote Transmitter idle while waiting for ACK Efficiency limited by round trip delay time Requires no storage of packetsThe stop and wait protocol • Original ARQ protocol • Sender transmits one packet at a time and waits for an ACK – Receiver A C K’s packets – Sender retransmits packet after a timeout PKT-0 X ACK-0 PKT-1 ACK-1 PKT-2 PKT-2 ACK-2 TO • Packet numbering – Sender numbers packets with sequence numbers (SN) – Receiver uses request numbers (RN) to ACK packets RN = j is the same as an ACK for packet j-1 • Note: – Transmitter idle while waiting for ACK – Efficiency limited by round trip delay time – Requires no storage of packets