Flow control - Revision history

Jnc: /* Serial lines */ typo

2021-10-18T12:47:28Z

‎Serial lines: typo

Jnc: +cat

2018-12-16T04:03:12Z

+cat

Jnc: Add serial line flow control

2018-09-30T19:59:17Z

Add serial line flow control

Jnc: A good start

2018-09-30T16:04:12Z

A good start

New page

'''Flow control''' refers to the need, with two [[application]] instances communicating over a [[byte stream]], to prevent the sender from sending data faster than the receiver can consume it.

When the two instances are on a single machine (e.g. using a [[pipe]] to communicate), flow control is fairly simple to peform; the [[operating system]] monitors the amount of data in the stream, and blocks the sender when the backlog gets too large.

Over a network, the problem is a little more complicated; the [[protocol]] has to have a mechanism to allow the destination to inform the source how much [[buffer]]ing is available for incoming data, or to tell the source that the destination cannot accept any more data at this time.

In the [[reliable byte stream]] [[Transmission Control Protocol|TCP]] protocol of the [[TCP/IP]] [[protocol family]], a '''window''' at the sender is maintained for this purpose; the receiver on each side periodically updates the window stored at the other end.

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 In [[asynchronous serial line]]s, a variety of techniques are used.
-With [[EIA RS-232 serial line interface|RS-232 interfaces]], there are a pair of control lines dedicated to doing flow control in [[hardware]] - Request To Send, and Clear To Send. The sender activates RTS when it has data ready; the receive puts up Clear To Send as long as it's OK for the sender to send.
+With [[EIA RS-232 serial line interface|RS-232 interfaces]], there are a pair of control lines dedicated to doing flow control in [[hardware]] - Request To Send, and Clear To Send. The sender activates RTS when it has data ready; the receiver puts up Clear To Send as long as it's OK for the sender to send.
 More commonly, serial lines also use [[software]] flow control, using in-band transmission of XOFF and XON [[character]]s: usually, but not nessarily, CTRL-S and CTRL-Q. (The formal [[ASCII]] specification does not reserve XON/XOFF characters.)

← Older revision		Revision as of 04:03, 16 December 2018
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	In the [[Transmission Control Protocol\|TCP]] [[reliable byte stream]] protocol of the [[TCP/IP]] [[protocol family]], a '''window''' at the sender is maintained for this purpose; the receiver on each side periodically updates the window stored at the other end.		In the [[Transmission Control Protocol\|TCP]] [[reliable byte stream]] protocol of the [[TCP/IP]] [[protocol family]], a '''window''' at the sender is maintained for this purpose; the receiver on each side periodically updates the window stored at the other end.
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		+	[[Category: Basics]]

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-'''Flow control''' refers to the need, with two [[application]] instances communicating over a [[byte stream]], to prevent the sender from sending data faster than the receiver can consume it.
+'''Flow control''' refers to the need to prevent a sender of data from sending it so fast the receiver cannot take it all in.
 When the two instances are on a single machine (e.g. using a [[pipe]] to communicate), flow control is fairly simple to peform; the [[operating system]] monitors the amount of data in the stream, and blocks the sender when the backlog gets too large.
@@ Line 5: / Line 17: @@
 Over a network, the problem is a little more complicated; the [[protocol]] has to have a mechanism to allow the destination to inform the source how much [[buffer]]ing is available for incoming data, or to tell the source that the destination cannot accept any more data at this time.
-In the [[reliable byte stream]] [[Transmission Control Protocol|TCP]] protocol of the [[TCP/IP]] [[protocol family]], a '''window''' at the sender is maintained for this purpose; the receiver on each side periodically updates the window stored at the other end.
+In the [[Transmission Control Protocol|TCP]] [[reliable byte stream]] protocol of the [[TCP/IP]] [[protocol family]], a '''window''' at the sender is maintained for this purpose; the receiver on each side periodically updates the window stored at the other end.