Lecture 7: Internet Applications #3.3: HTTP/1.1

HTTP/1.1 Basics

HTTP/1.1 (rfc2616) is now in widespread use. It extends the older protocol in a number of areas, notably persistent connections/pipelining and support for caching.

To implement Persisent Connections, HTTP/1.1 introduced a new request (and also response) header called "Connection:". This can take two values: "close" (which means that this is not a persistent connection) and "keep-alive", which means that the TCP connection is held until either side sends a "Connection: close" header, indicating that it wishes to terminate after the current transfer.

The browser can utilise a persistent connection by sending multiple requests over the connection without stopping and waiting for each them to be satisfied before sending the next -- the reponses are "in the pipeline". Similarly, the server can respond with responses sent one after another another. This is possible because each request can be unambiguously identified, as can the responses, using the "Content-length:" headers. The huge wins here, obviously, are that there's no delay opening multiple TCP connections, and the slow-start algorithm has time to get up to full speed.

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