Multiplexing
Multiplexing allows multiple logical streams to share a single connection or channel. HTTP/2 multiplexes many requests over one TCP connection using stream IDs. Port numbers multiplex connections at the transport layer. Without multiplexing, each request needs its own connection – wasting resources.
Definition
Multiplexing is sharing a single physical or logical channel among multiple independent data streams. In networking, multiplexing appears at every layer. Port numbers multiplex multiple applications over a single IP address. HTTP/2 multiplexes hundreds of request/response pairs over one TCP connection using 31-bit stream identifiers – eliminating HTTP/1.1's head-of-line blocking at the application layer (though TCP-level HOL blocking remains). QUIC multiplexes streams over UDP with independent loss recovery per stream – one lost packet only stalls its own stream. Frequency-division multiplexing (FDM) in fiber optics carries multiple wavelengths simultaneously. Time-division multiplexing (TDM) in cellular networks allocates time slots to different users.
Examples
- –HTTP/2: HEADERS frame stream=1, DATA frame stream=3, HEADERS frame stream=5 – all on one TCP connection
- –TCP port numbers: port 80 and 443 on the same IP = two multiplexed services
- –QUIC stream 4 retransmits independently while stream 6 continues delivering