Half-Duplex

A communication mode where data can flow in both directions between two endpoints, but only in one direction at a time. Classic HTTP/1.1 request-response is half-duplex: the client sends a complete request, then waits for the server's complete response before the next exchange can begin. FTP's control channel also operates half-duplex. The alternating nature of half-duplex limits throughput for high-bandwidth bidirectional workloads, which is why WebSocket and HTTP/2 introduced full-duplex capabilities.