- Timestamp:
- 19/01/13 00:18:13 (10 years ago)
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- 1 edited
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draft-ietf-httpbis-http2/latest/draft-ietf-httpbis-http2.xml
r2125 r2127 431 431 </section> 432 432 433 <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> 436 496 437 497 <section title="Control frame types"> … … 1313 1373 1314 1374 <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> 1320 1393 </t> 1394 1321 1395 </section> 1322 1396 </middle> … … 1543 1617 </t> 1544 1618 <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"/>. 1546 1621 </t> 1547 1622 <t> … … 1553 1628 <t> 1554 1629 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"/>. 1555 1634 </t> 1556 1635 </section>
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