One request, start to finish

Every HTTP/2 connection opens with both sides sending SETTINGS, and each acknowledges the other's (RFC 9113 §3.4, RFC 9113 §6.5.3). The client's side of that opening actually starts with a fixed 24-octet preface, "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n" (RFC 9113 §3.4), which this hub does not draw. The client need not wait for the exchange to finish: once the server's SETTINGS has landed, it opens stream 1 with a HEADERS frame, before its own SETTINGS is acknowledged (RFC 9113 §3.4). A GET has no body, so that frame carries END_STREAM, and the stream is half-closed on the client's side at once. The server answers with its own HEADERS and two DATA frames. END_STREAM on the last one closes the stream (RFC 9113 §5.1).

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 15

Streams at this step
s0	connection SET	1 frames
s1	index	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), 65 535 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: 65 535
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.