Hypertext Transfer Protocol Version 2 (HTTP/2)
RFC 7540

Document Type RFC - Proposed Standard (May 2015; Errata)
Last updated 2015-11-18
Replaces draft-mbelshe-httpbis-spdy
Stream IETF
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Stream WG state Submitted to IESG for Publication Jun 2014
Document shepherd Mark Nottingham
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IESG IESG state RFC 7540 (Proposed Standard)
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IANA IANA review state Version Changed - Review Needed
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Internet Engineering Task Force (IETF)                         M. Belshe
Request for Comments: 7540                                         BitGo
Category: Standards Track                                        R. Peon
ISSN: 2070-1721                                              Google, Inc
                                                         M. Thomson, Ed.
                                                                 Mozilla
                                                                May 2015

             Hypertext Transfer Protocol Version 2 (HTTP/2)

Abstract

   This specification describes an optimized expression of the semantics
   of the Hypertext Transfer Protocol (HTTP), referred to as HTTP
   version 2 (HTTP/2).  HTTP/2 enables a more efficient use of network
   resources and a reduced perception of latency by introducing header
   field compression and allowing multiple concurrent exchanges on the
   same connection.  It also introduces unsolicited push of
   representations from servers to clients.

   This specification is an alternative to, but does not obsolete, the
   HTTP/1.1 message syntax.  HTTP's existing semantics remain unchanged.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7540.

Belshe, et al.               Standards Track                    [Page 1]
RFC 7540                         HTTP/2                         May 2015

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................4
   2. HTTP/2 Protocol Overview ........................................5
      2.1. Document Organization ......................................6
      2.2. Conventions and Terminology ................................6
   3. Starting HTTP/2 .................................................7
      3.1. HTTP/2 Version Identification ..............................8
      3.2. Starting HTTP/2 for "http" URIs ............................8
           3.2.1. HTTP2-Settings Header Field .........................9
      3.3. Starting HTTP/2 for "https" URIs ..........................10
      3.4. Starting HTTP/2 with Prior Knowledge ......................10
      3.5. HTTP/2 Connection Preface .................................11
   4. HTTP Frames ....................................................12
      4.1. Frame Format ..............................................12
      4.2. Frame Size ................................................13
      4.3. Header Compression and Decompression ......................14
   5. Streams and Multiplexing .......................................15
      5.1. Stream States .............................................16
           5.1.1. Stream Identifiers .................................21
           5.1.2. Stream Concurrency .................................22
      5.2. Flow Control ..............................................22
           5.2.1. Flow-Control Principles ............................23
           5.2.2. Appropriate Use of Flow Control ....................24
      5.3. Stream Priority ...........................................24
           5.3.1. Stream Dependencies ................................25
           5.3.2. Dependency Weighting ...............................26
           5.3.3. Reprioritization ...................................26
           5.3.4. Prioritization State Management ....................27
           5.3.5. Default Priorities .................................28
      5.4. Error Handling ............................................28
           5.4.1. Connection Error Handling ..........................29
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