Ignore:
Timestamp:
19/01/13 00:18:13 (9 years ago)
Author:
martin.thomson@…
Message:

Adding flow control principles.

File:
1 edited

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  • draft-ietf-httpbis-http2/latest/draft-ietf-httpbis-http2.html

    r2125 r2127  
    406406  }
    407407  @bottom-center {
    408        content: "Expires July 20, 2013";
     408       content: "Expires July 22, 2013";
    409409  }
    410410  @bottom-right {
     
    447447      <meta name="dct.creator" content="Melnikov, A.">
    448448      <meta name="dct.identifier" content="urn:ietf:id:draft-ietf-httpbis-http2-latest">
    449       <meta name="dct.issued" scheme="ISO8601" content="2013-01-16">
     449      <meta name="dct.issued" scheme="ISO8601" content="2013-01-18">
    450450      <meta name="dct.abstract" content="This document describes an optimised expression of the semantics of the HTTP protocol. The HTTP/2.0 encapsulation enables more efficient transfer of resources over HTTP by providing compressed headers, simultaneous requests, and unsolicted push of resources from server to client. This document is an alternative to, but does not obsolete RFC{http-p1}. The HTTP protocol semantics described in RFC{http-p2..p7} are unmodified.">
    451451      <meta name="description" content="This document describes an optimised expression of the semantics of the HTTP protocol. The HTTP/2.0 encapsulation enables more efficient transfer of resources over HTTP by providing compressed headers, simultaneous requests, and unsolicted push of resources from server to client. This document is an alternative to, but does not obsolete RFC{http-p1}. The HTTP protocol semantics described in RFC{http-p2..p7} are unmodified.">
     
    467467            </tr>
    468468            <tr>
    469                <td class="left">Expires: July 20, 2013</td>
     469               <td class="left">Expires: July 22, 2013</td>
    470470               <td class="right">Google, Inc</td>
    471471            </tr>
     
    488488            <tr>
    489489               <td class="left"></td>
    490                <td class="right">January 16, 2013</td>
     490               <td class="right">January 18, 2013</td>
    491491            </tr>
    492492         </tbody>
     
    521521         in progress”.
    522522      </p>
    523       <p>This Internet-Draft will expire on July 20, 2013.</p>
     523      <p>This Internet-Draft will expire on July 22, 2013.</p>
    524524      <h1><a id="rfc.copyrightnotice" href="#rfc.copyrightnotice">Copyright Notice</a></h1>
    525525      <p>Copyright © 2013 IETF Trust and the persons identified as the document authors. All rights reserved.</p>
     
    569569                  </ul>
    570570               </li>
    571                <li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.5">Data flow</a></li>
     571               <li><a href="#rfc.section.3.5">3.5</a>&nbsp;&nbsp;&nbsp;<a href="#flowcontrol">Stream Flow Control</a><ul>
     572                     <li><a href="#rfc.section.3.5.1">3.5.1</a>&nbsp;&nbsp;&nbsp;<a href="#fc-principles">Flow Control Principles</a></li>
     573                     <li><a href="#rfc.section.3.5.2">3.5.2</a>&nbsp;&nbsp;&nbsp;<a href="#fc-basic">Basic Flow Control Algorithm</a></li>
     574                  </ul>
     575               </li>
    572576               <li><a href="#rfc.section.3.6">3.6</a>&nbsp;&nbsp;&nbsp;<a href="#rfc.section.3.6">Control frame types</a><ul>
    573577                     <li><a href="#rfc.section.3.6.1">3.6.1</a>&nbsp;&nbsp;&nbsp;<a href="#SYN_STREAM">SYN_STREAM</a></li>
     
    934938         There is no reason to send a RST_STREAM for each frame in succession).
    935939      </p>
    936       <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;Data flow
    937       </h2>
    938       <p id="rfc.section.3.5.p.1">Because TCP provides a single stream of data on which HTTP/2.0 multiplexes multiple logical streams, clients and servers must
    939          intelligently interleave data messages for concurrent sessions.
    940       </p>
     940      <h2 id="rfc.section.3.5"><a href="#rfc.section.3.5">3.5</a>&nbsp;<a id="flowcontrol" href="#flowcontrol">Stream Flow Control</a></h2>
     941      <p id="rfc.section.3.5.p.1">Multiplexing streams introduces contention for access to the shared TCP connection. Stream contention can result in streams
     942         being blocked by other streams. A flow control scheme ensures that streams do not destructively interfere with other streams
     943         on the same TCP connection.
     944      </p>
     945      <h3 id="rfc.section.3.5.1"><a href="#rfc.section.3.5.1">3.5.1</a>&nbsp;<a id="fc-principles" href="#fc-principles">Flow Control Principles</a></h3>
     946      <p id="rfc.section.3.5.1.p.1">Experience with TCP congestion control has shown that algorithms can evolve over time to become more sophisticated without
     947         requiring protocol changes. TCP congestion control and its evolution is clearly different from HTTP/2.0 flow control, though
     948         the evolution of TCP congestion control algorithms shows that a similar approach could be feasible for HTTP/2.0 flow control.
     949      </p>
     950      <p id="rfc.section.3.5.1.p.2">HTTP/2.0 stream flow control aims to allow for future improvements to flow control algorithms without requiring protocol changes.
     951         The following principles guide the HTTP/2.0 design:
     952      </p>
     953      <ol>
     954         <li>Flow control is hop-by-hop, not end-to-end.</li>
     955         <li>Flow control is based on window update messages. Receivers advertise how many octets they are prepared to receive on a stream.
     956            This is a credit-based scheme.
     957         </li>
     958         <li>Flow control is directional with overall control provided by the receiver. A receiver MAY choose to set any window size that
     959            it desires for each stream [[TBD: ... and for the overall connection]]. A sender MUST respect flow control limits imposed
     960            by a receiver. Clients, servers and intermediaries all independently advertise their flow control preferences as a receiver
     961            and abide by the flow control limits set by their peer when sending.
     962         </li>
     963         <li>Flow control can be disabled by a receiver. A receiver can choose to either disable flow control, or to declare an infinite
     964            flow control limit. [[TBD: determine whether just one mechanism is sufficient, and then which alternative]]
     965         </li>
     966         <li>HTTP/2.0 standardizes only the format of the window update message (<a href="#WINDOW_UPDATE" title="WINDOW_UPDATE">Section&nbsp;3.6.8</a>). This does not stipulate how a receiver decides when to send this message or the value that it sends. Nor does it specify
     967            how a sender chooses to send packets. Implementations are able to select any algorithm that suits their needs. An example
     968            flow control algorithm is described in <a href="#fc-basic" title="Basic Flow Control Algorithm">Section&nbsp;3.5.2</a>.
     969         </li>
     970      </ol>
     971      <p id="rfc.section.3.5.1.p.3">Implementations are also responsible for managing how requests and responses are sent based on priority; choosing how to avoid
     972         head of line blocking for requests; and managing the creation of new streams. Algorithm choices for these could interact with
     973         any flow control algorithm.
     974      </p>
     975      <h3 id="rfc.section.3.5.2"><a href="#rfc.section.3.5.2">3.5.2</a>&nbsp;<a id="fc-basic" href="#fc-basic">Basic Flow Control Algorithm</a></h3>
     976      <p id="rfc.section.3.5.2.p.1">This section describes a basic flow control algorithm. This algorithm is provided as an example, implementations can use any
     977         algorithm that complies with flow control requirements.
     978      </p>
     979      <p id="rfc.section.3.5.2.p.2">[[Algorithm TBD]]</p>
    941980      <h2 id="rfc.section.3.6"><a href="#rfc.section.3.6">3.6</a>&nbsp;Control frame types
    942981      </h2>
     
    19832022      <h1 id="rfc.section.9"><a href="#rfc.section.9">9.</a>&nbsp;Acknowledgements
    19842023      </h1>
    1985       <p id="rfc.section.9.p.1">Prior to being used as the basis for HTTP/2.0, the following individuals contributed to the design and evolution of SPDY:
    1986          Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe
    1987          Chan, Adam Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay, Paul Amer, Fan Yang, Jonathan Leighton.
    1988       </p>
     2024      <p id="rfc.section.9.p.1">This document includes substantial input from the following individuals: </p>
     2025      <ul>
     2026         <li>Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe
     2027            Chan, Adam Barth, Ryan Hamilton, Gavin Peters, Kent Alstad, Kevin Lindsay, Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).
     2028         </li>
     2029         <li>Gabriel Montenegro and Willy Tarreau (Upgrade mechanism)</li>
     2030         <li>William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro, Jitu Padhye, Roberto Peon, Rob Trace (Flow control principles)</li>
     2031         <li>Mark Nottingham and Julian Reschke</li>
     2032      </ul>
    19892033      <h1 id="rfc.references"><a href="#rfc.section.10" id="rfc.section.10">10.</a> Normative References
    19902034      </h1>
     
    20802124      <p id="rfc.section.A.1.p.5">Added section on starting HTTP/2.0, including upgrade mechanism.</p>
    20812125      <p id="rfc.section.A.1.p.6">Removed unused references.</p>
     2126      <p id="rfc.section.A.1.p.7">Added flow control principles (<a href="#fc-principles" title="Flow Control Principles">Section&nbsp;3.5.1</a>) based on &lt;<a href="http://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01">http://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01</a>&gt;.
     2127      </p>
    20822128      <h2 id="rfc.section.A.2"><a href="#rfc.section.A.2">A.2</a>&nbsp;<a id="changes.since.draft-mbelshe-httpbis-spdy-00" href="#changes.since.draft-mbelshe-httpbis-spdy-00">Since draft-mbelshe-httpbis-spdy-00</a></h2>
    20832129      <p id="rfc.section.A.2.p.1">Adopted as base for draft-ietf-httpbis-http2.</p>
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