Browse Prior Art Database

Method of Flow Control for V.24 Interfaces

IP.com Disclosure Number: IPCOM000121859D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 3 page(s) / 68K

Publishing Venue

IBM

Related People

Petty, JS: AUTHOR

Abstract

Modems that do internal error detection and re-transmission must have ways to force an attached DTE to stop transmitting data. Both the DTE and DCE must support some flow control method or the DCE's transmit data buffer may overflow causing loss of data.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 75% of the total text.

Method of Flow Control for V.24 Interfaces

      Modems that do internal error detection and
re-transmission must have ways to force an attached DTE to stop
transmitting data.  Both the DTE and DCE must support some flow
control method or the DCE's transmit data buffer may overflow causing
loss of data.

      Two methods exist in prior art.  One is inactivation of the
Clear to Send (CTS) signal by the DCE when the buffer is almost full.
This method is sometimes called "hardware" flow control.  The second
method is delivery of Device Control characters, such as XON and XOFF
in the ASCII and IA5 character sets, from the DCE to the DTE.  This
second method is sometimes called "software" flow control. Generally,
the modems have switches that allow the customer to configure the
modem to match the DTE.

      There are DTEs that treat Device Control characters as data and
there are DTEs that treat a drop of CTS while Request to Send (RTS)
is active as a modem failure.  There are also DTEs that do both.

      Fig. 1 shows the basic principle of flow control when a DCE is
accepting data from a DTE for delivery to a telecommunication line.

      Fig. 2 shows a new method of flow control making use of the
fact that many DTEs, especially older ones, are capable of supporting
half duplex modems - modems that require the DTE to raise RTS and
wait for CTS before sending each block of data.

      Note that in almost all of the modems that use data buffers,...