HTTP (Hypertext Transfer Protocol) operates at the application layer of the Internet protocol suite and relies on the underlying layers to provide essential network functions. HTTP depends on the transport layer, primarily the Transmission Control Protocol (TCP), to establish reliable connections between clients and servers for sending and receiving requests and responses. TCP ensures reliable, ordered delivery of data packets, which allows HTTP to transfer hypertext and other web resources correctly. Starting with HTTP/3, HTTP uses QUIC, which runs over UDP and provides similar reliability. Below HTTP, the Internet layers include:
- Network layer (Internet Protocol, IP) for routing packets between devices.
- Data link and physical layers for actual data transmission over various hardware.
HTTP itself is a stateless, extensible protocol designed to work over this layered architecture, utilizing the reliable transport services below to enable web browsing, resource fetching, caching, proxies, and session management through cookies. In summary, HTTP relies on the lower network and transport layers for addressing, routing, connection establishment, and reliable data transfer, allowing HTTP to focus on application semantics like request/response and content delivery.