Persistent and No persistent Connections
HTTP can use both persistent and non persistent connection. By defaults uses persistent connections.
Persistent Connections
HTTP persistent connection also called HTTP keep alive or HTTP connection reuses is the idea of using the same TCP connection to send and receive multiple HTTP request / responses as opposed to opening a new one for every single request/ response pair using persistent connections is very important for improving HTTP performance.
HTTP specifies a persistent connection by default. With persistent connection the server leaves the TCP connection open after sending a response. Subsequent request an denture web page can be sent over a single persistent TCP connection moreover multiple web pages residing on the same server can be sent from the server to same client over a single persistent TCP connection. The HTTP server close a connection when it isn't used for certain time ( a configurable time out interval).
These are several advantages of using persistent connections including:
a.Network friendly less network traffic due to fewer setting up and tearing down of TCP connections.
b.Reduced latency on subsequent request. Due to avoidance of initial TCP handshake.
c.Long lasting connection allowing TCP sufficient time to determine the congestion state of the network thus to react appropriately.
There are two versions of persistent connections.