HTTP 1.1
Better version of HTTP 1 which introduce the keep-alive
which use the same TCP (Transmission Control Protocol) connection.
On the left side we have HTTP 1 whereas on the right handside is HTTP 1.1
Pipelining
HTTP 1.1 also add Pipelining which allows client and server sends multiple requests before waiting for a response.
For example:
The responses needs to be retrieve in order with the requests
Problem
The pipelining is very hard to implement and most of the proxies server are not implementing it correctly. Some browsers drop support for HTTP 1.1 because it has many issues.
Head of line blocking
Since the subsequent requests must wait for the first request to complete, it might be blocked and then extends the time a client have to wait to close the TCP (Transmission Control Protocol).