Re: [quicwg/base-drafts] QUIC flow control is not quite like HTTP/2 (#3766)

Martin Thomson <> Tue, 16 June 2020 01:31 UTC

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Date: Mon, 15 Jun 2020 18:30:36 -0700
From: Martin Thomson <>
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Subject: Re: [quicwg/base-drafts] QUIC flow control is not quite like HTTP/2 (#3766)
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@martinthomson approved this pull request.

> @@ -792,10 +792,9 @@ is not excessive buffering at multiple layers.
 ## Data Flow Control {#data-flow-control}
-QUIC employs a credit-based flow-control scheme similar to that in HTTP/2
-{{?HTTP2}}, where a receiver advertises the number of bytes it is prepared to
-receive on a given stream and for the entire connection.  This leads to two
-levels of data flow control in QUIC:
+QUIC employs a limit-based flow-control scheme similar, where a receiver

QUIC employs a limit-based flow-control scheme where a receiver

> -A receiver MAY send MAX_STREAM_DATA frames in multiple packets in order to make
-sure that the sender receives an update before running out of flow control
-credit, even if one of the packets is lost.
-A receiver advertises credit for a connection by sending a MAX_DATA frame, which
-indicates the maximum of the sum of the absolute byte offsets of all streams.  A
-receiver maintains a cumulative sum of bytes received on all streams, which is
-used to check for flow control violations. A receiver might use a sum of bytes
-consumed on all streams to determine the maximum data limit to be advertised.
-A receiver can advertise a larger offset by sending MAX_STREAM_DATA or MAX_DATA
-frames.  Once a receiver advertises an offset, it MAY advertise a smaller
-offset, but this has no effect.
+frames to the sender to advertise larger limits.
+A receiver can advertise a larger limit for a stream by sending a MAX_STREAM_DATA

"can advertise a larger limit" or "can increase the limit for a stream"

> @@ -845,7 +844,7 @@ is flow control limited SHOULD periodically send a STREAM_DATA_BLOCKED or
 DATA_BLOCKED frame when it has no ack-eliciting packets in flight.
-## Flow Credit Increments {#fc-credit}
+## Incrementing Flow Control {#fc-credit}

## Increasing Flow Control Limits {#fc-credit}

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