[Editorial Errata Reported] RFC7540 (4871)

[RFC Errata System <[e-mail]>]

The following errata report has been submitted for RFC7540,
"Hypertext Transfer Protocol Version 2 (HTTP/2)".

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You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=7540&eid=4871

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Type: Editorial
Reported by: Martin Thomson <[e-mail]>

Section: 5.3.4

Original Text
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For example, assume streams A and B share a parent, and streams C
and D both depend on stream A. Prior to the removal of stream A,
if streams A and D are unable to proceed, then stream C receives
all the resources dedicated to stream A. If stream A is removed
from the tree, the weight of stream A is divided between streams
C and D. If stream D is still unable to proceed, this results in
stream C receiving a reduced proportion of resources. For equal
starting weights, C receives one third, rather than one half, of
available resources.

Corrected Text
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For example, assume streams A and B share a parent, and streams C
and D both depend on stream A. When A is complete, streams C and
D receive all the resources that would be allocated to stream
A. If stream D is unable to proceed, stream C shares resources
with stream B. Assuming equal starting weights on all streams,
this means that streams B and C receive an equal share.  However,
if stream A is removed from the tree, the weight of stream A is
divided between streams C and D. With stream A removed and stream
D unable to proceed, stream C receives a reduced proportion of
resources. For equal starting weights, C receives one third,
rather than one half, of available resources.

Notes
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The example was incorrect.  Dependent streams do not receive resources if their parent is blocked; they only receive resources once the parent is complete.

Note that I didn't correct the common misunderstanding regarding the third here.  That might be further improved by doing the math.  That is:

Before removal: A=N (C=N, D=N), B=N;
After removal: B=N, C=N/2, D=N/2;
Therefore viable streams are B=N and C=N/2 meaning a total pool of 3N/2.  The resource proportion allocated to C is therefore (N/2)/(3N/2)=1/3.

But that would probably need an entire section for the example, rather than a single paragraph.

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RFC7540 (draft-ietf-httpbis-http2-17)
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Title               : Hypertext Transfer Protocol Version 2 (HTTP/2)
Publication Date    : May 2015
Author(s)           : M. Belshe, R. Peon, M. Thomson, Ed.
Category            : PROPOSED STANDARD
Source              : Hypertext Transfer Protocol Bis APP
Area                : Applications
Stream              : IETF
Verifying Party     : IESG