Why Stop-and-Wait ARQ Leaves Fast Links Underused Over Long Distances

Engineers deploying high-speed fiber across continents often find that raising bandwidth from 1 Gbps to 10 Gbps barely improves throughput for single-packet protocols. The article attributes this to propagation delay, the time signals need to cross the physical distance, which dominates over transmission time. In Stop-and-Wait ARQ, the sender pauses after each frame until an acknowledgment returns, so channel utilization is computed as 1/(1+2a), where a is the ratio of propagation to transmission delay. Utilization stays near 100 percent on short local networks but drops toward zero on wide-area and satellite links, and faster bandwidth only increases a and worsens the problem. The article notes that sliding window protocols such as Go-Back-N, Selective Repeat, and TCP pipeline multiple frames to keep high-latency links saturated.