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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Added
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  • draft-ietf-httpbis-http2/latest/draft-ietf-httpbis-http2.xml

    r2125 r2127  
    431431      </section>
    432432
    433       <section title="Data flow">
    434 <t>Because TCP provides a single stream of data on which HTTP/2.0 multiplexes multiple logical streams, clients and servers must intelligently interleave data messages for concurrent sessions.</t>
    435       </section>
     433<section anchor="flowcontrol" title="Stream Flow Control">
     434<t>
     435  Multiplexing streams introduces contention for access to the shared TCP connection.  Stream
     436  contention can result in streams being blocked by other streams.  A flow control scheme ensures
     437  that streams do not destructively interfere with other streams on the same TCP connection.
     438</t>
     439
     440<section anchor="fc-principles" title="Flow Control Principles">
     441<t>
     442  Experience with TCP congestion control has shown that algorithms can evolve over time
     443  to become more sophisticated without requiring protocol changes.  TCP congestion control and its
     444  evolution is clearly different from HTTP/2.0 flow control, though the evolution of TCP congestion
     445  control algorithms shows that a similar approach could be feasible for HTTP/2.0 flow control.
     446</t>
     447<t>
     448  HTTP/2.0 stream flow control aims to allow for future improvements to flow control algorithms
     449  without requiring protocol changes.  The following principles guide the HTTP/2.0 design:
     450  <list style="numbers">
     451    <t>
     452      Flow control is hop-by-hop, not end-to-end.
     453    </t>
     454    <t>
     455      Flow control is based on window update messages.  Receivers advertise how many octets they are
     456      prepared to receive on a stream.  This is a credit-based scheme.
     457    </t>
     458    <t>
     459      Flow control is directional with overall control provided by the receiver.  A receiver MAY
     460      choose to set any window size that it desires for each stream [[TBD: ... and for the overall
     461      connection]].  A sender MUST respect flow control limits imposed by a receiver.  Clients,
     462      servers and intermediaries all independently advertise their flow control preferences as a
     463      receiver and abide by the flow control limits set by their peer when sending.
     464    </t>
     465    <t>
     466      Flow control can be disabled by a receiver.  A receiver can choose to either disable flow
     467      control, or to declare an infinite flow control limit.  [[TBD: determine whether just one
     468      mechanism is sufficient, and then which alternative]]
     469    </t>
     470    <t>
     471      HTTP/2.0 standardizes only the format of the <xref target="WINDOW_UPDATE">window update
     472      message</xref>.  This does not stipulate how a receiver decides when to send this message or
     473      the value that it sends.  Nor does it specify how a sender chooses to send packets.
     474      Implementations are able to select any algorithm that suits their needs.  An example flow
     475      control algorithm is described in <xref target="fc-basic"/>.
     476    </t>
     477  </list>
     478</t>
     479<t>
     480  Implementations are also responsible for managing how requests and responses are sent based on
     481  priority; choosing how to avoid head of line blocking for requests; and managing the creation of
     482  new streams.  Algorithm choices for these could interact with any flow control algorithm.
     483</t>
     484
     485</section>
     486<section anchor="fc-basic" title="Basic Flow Control Algorithm">
     487<t>
     488  This section describes a basic flow control algorithm.  This algorithm is provided as an example,
     489  implementations can use any algorithm that complies with flow control requirements.
     490</t>
     491<t>
     492  [[Algorithm TBD]]
     493</t>
     494</section>
     495</section>
    436496
    437497      <section title="Control frame types">
     
    13131373
    13141374<section title="Acknowledgements">
    1315   <t>
    1316     Prior to being used as the basis for HTTP/2.0, the following individuals contributed to the
    1317     design and evolution of SPDY: Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa
    1318     Wilk, Costin Manolache, William Chan, Vitaliy Lvin, Joe Chan, Adam Barth, Ryan Hamilton, Gavin
    1319     Peters, Kent Alstad, Kevin Lindsay, Paul Amer, Fan Yang, Jonathan Leighton.
     1375  <t>This document includes substantial input from the following individuals:
     1376  <list style="symbols">
     1377    <t>
     1378      Adam Langley, Wan-Teh Chang, Jim Morrison, Mark Nottingham, Alyssa Wilk, Costin Manolache,
     1379      William Chan, Vitaliy Lvin, Joe Chan, Adam Barth, Ryan Hamilton, Gavin Peters, Kent Alstad,
     1380      Kevin Lindsay, Paul Amer, Fan Yang, Jonathan Leighton (SPDY contributors).
     1381    </t>
     1382    <t>
     1383      Gabriel Montenegro and Willy Tarreau (Upgrade mechanism)
     1384    </t>
     1385    <t>
     1386      William Chan, Salvatore Loreto, Osama Mazahir, Gabriel Montenegro, Jitu Padhye, Roberto Peon,
     1387      Rob Trace (Flow control principles)
     1388    </t>
     1389    <t>
     1390      Mark Nottingham and Julian Reschke
     1391    </t>
     1392  </list>
    13201393  </t>
     1394
    13211395</section>
    13221396</middle>
     
    15431617</t>
    15441618<t>
    1545   Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <eref target="https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU"/>.
     1619  Changed INTERNAL_ERROR on GOAWAY to have a value of 2 <eref
     1620  target="https://groups.google.com/forum/?fromgroups#!topic/spdy-dev/cfUef2gL3iU"/>.
    15461621</t>
    15471622<t>
     
    15531628<t>
    15541629  Removed unused references.
     1630</t>
     1631<t>
     1632  Added <xref target="fc-principles">flow control principles</xref> based on <eref
     1633  target="http://tools.ietf.org/html/draft-montenegro-httpbis-http2-fc-principles-01"/>.
    15551634</t>
    15561635</section>
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