Network Working Group R. Fielding Request for Comments: 2616 ...

how the transfer-length of a message-body is determined.Fielding, et al. Standards Track [Page 43]RFC 2616 HTTP/1.1 June 19998 Connections8.1 Persistent Connections8.1.1 PurposePrior to persistent connections, a separate TCP connection wasestablished to fetch each URL, increasing the load on HTTP serversand causing congestion on the Internet. The use of inline images andother associated data often require a client to make multiplerequests of the same server in a short amount of time. Analysis ofthese performance problems and results from a prototypeimplementation are available [26] [30]. Implementation experience andmeasurements of actual HTTP/1.1 (RFC 2068) implementations show goodresults [39]. Alternatives have also been explored, for example,T/TCP [27].Persistent HTTP connections have a number of advantages:- By opening and closing fewer TCP connections, CPU time is savedin routers and hosts (clients, servers, proxies, gateways,tunnels, or caches), and memory used for TCP protocol controlblocks can be saved in hosts.- HTTP requests and responses can be pipelined on a connection.Pipelining allows a client to make multiple requests withoutwaiting for each response, allowing a single TCP connection tobe used much more efficiently, with much lower elapsed time.- Network congestion is reduced by reducing the number of packetscaused by TCP opens, and by allowing TCP sufficient time todetermine the congestion state of the network.