The same download, with the window out of the way

The same 200 000-byte download, with a client that widens both windows. Its SETTINGS announces INITIAL_WINDOW_SIZE 1 048 576, which sets every stream's window (RFC 9113 §6.5.2). SETTINGS cannot change the connection's window, which starts at 65 535 bytes (RFC 9113 §6.9.2), so straight after its SETTINGS the client sends a WINDOW_UPDATE on stream 0 that raises it to 1 048 576 too. No DATA frame waits for credit, and the client sends no other WINDOW_UPDATE: the server puts its frames on the wire back to back, at the link's speed. Compare narrow-window: the same link and server, a window 64 times smaller, and a download that takes nearly three times as long. shared-pipe shows the connection window on its own.

Connection · one pipe, many streams

DATA: a block as wide as its time on the wire, in its stream's colour
HEADERS: hatched
SETTINGS, ACK, PING, WINDOW_UPDATE, GOAWAY: a tick with a glyph
RST_STREAM: a cut; NO_ERROR is not a failure
END_STREAM: a thick trailing edge
a window: the filled part is the credit left, in bytes, not in time
a gauge for a stream with no window yet: dashed, not the same as empty
bytes ready with no credit
current frame
in flight: from its last byte to its landing at the other end
why: the frame whose landing set the current one off
faded: not sent yet
close ticks step to a second line so two close glyphs don't overlap

The pipe

client windows

server windows

Step 0 of 39

Streams at this step
s0	connection SET	1 frames
s1	big	not open yet

Frame

Reset

Step 0 · SETTINGS · stream 0 · leaves client → server

The client sends its SETTINGS

Before any frame, the client sends the 24-octet connection preface, PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n. RFC 9113 §3.4 chose it so that a large proportion of HTTP/1.x servers and intermediaries do not process further frames. It is not a frame, so it is not drawn. Then SETTINGS states what the client will accept: frames of up to 16 384 bytes (MAX_FRAME_SIZE), 1 048 576 bytes per stream before the server must wait for more window (INITIAL_WINDOW_SIZE). It also turns server push off (ENABLE_PUSH 0); the hub does not model it anyway.

moment: leaves the client
sent at: 0 ms
received at: 21 ms
length: 18 bytes
flags: none

Settings

SETTINGS_ENABLE_PUSH: 0
SETTINGS_INITIAL_WINDOW_SIZE: 1 048 576
SETTINGS_MAX_FRAME_SIZE: 16 384

RFC 9113 §3.4 · RFC 9113 §6.5.2

Lifecycle

RFC 9113 §5.1

ES is END_STREAM. Select a state to read about it. RFC 9113 §5.1 also has two reserved states for server push; they are left out because push is not modelled.