The Hypertext Transfer Protocol (HTTP) is a wildly successful
   protocol.  However, the way HTTP/1.1 uses the underlying transport
   ([RFC7230], Section 6) has several characteristics that have a
   negative overall effect on application performance today.

   In particular, HTTP/1.0 allowed only one request to be outstanding at
   a time on a given TCP connection.  HTTP/1.1 added request pipelining,
   but this only partially addressed request concurrency and still
   suffers from head-of-line blocking.  Therefore, HTTP/1.0 and HTTP/1.1
   clients that need to make many requests use multiple connections to a
   server in order to achieve concurrency and thereby reduce latency.

   Furthermore, HTTP header fields are often repetitive and verbose,
   causing unnecessary network traffic as well as causing the initial
   TCP [TCP] congestion window to quickly fill.  This can result in
   excessive latency when multiple requests are made on a new TCP
   connection.

   HTTP/2 addresses these issues by defining an optimized mapping of
   HTTP's semantics to an underlying connection.  Specifically, it
   allows interleaving of request and response messages on the same
   connection and uses an efficient coding for HTTP header fields.  It
   also allows prioritization of requests, letting more important
   requests complete more quickly, further improving performance.









Belshe, et al.               Standards Track                    [Page 4]
RFC 7540                         HTTP/2                         May 2015


   The resulting protocol is more friendly to the network because fewer
   TCP connections can be used in comparison to HTTP/1.x.  This means
   less competition with other flows and longer-lived connections, which
   in turn lead to better utilization of available network capacity.

   Finally, HTTP/2 also enables more efficient processing of messages
   through use of binary message framing.