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HTTP2 question about setting the initial connection window size

From: Kevin Grigorenko <kevin.grigorenko@us.ibm.com>
Date: Mon, 9 Jan 2023 15:14:31 +0000
To: "ietf-http-wg@w3.org" <ietf-http-wg@w3.org>
Message-ID: <SJ0PR15MB4421BF2FD0210F2FB1665BC6A3FE9@SJ0PR15MB4421.namprd15.prod.outlook.com>
Hi, I'm looking into enhancing the Wireshark HTTP2 dissector to track the connection and session window sizes to investigate flow control bottlenecks. I have a question about RFC9113 6.9.2:

"When an HTTP/2 connection is first established, new streams are created with an initial flow-control window size of 65,535 octets. The connection flow-control window is also 65,535 octets. Both endpoints can adjust the initial window size for new streams by including a value for SETTINGS_INITIAL_WINDOW_SIZE in the SETTINGS frame. The connection flow-control window can only be changed using WINDOW_UPDATE frames."

Does the last sentence mean that the connection flow-control window size can only be changed using a WINDOW_UPDATE frame _after_ the SETTINGS_INITIAL_WINDOW_SIZE?

In other words, does SETTINGS_INITIAL_WINDOW_SIZE also apply to the initial connection flow-control window size?

Kevin Grigorenko
IBM Automation Portfolio SWAT - App Platform, Software Engineer
Received on Monday, 9 January 2023 21:31:37 UTC

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