Ports
Flow Control
8-19
For example, the SCS will assert RTS when it is ready to accept data. When it can no longer accept data (its
buffers are full) it will deassert this signal. A connected modem will monitor the assertion and deassertion
of this signal; it will only send data when RTS is asserted.
A modem will assert CTS when it is ready to accept data. When its buffers are full, it will deassert CTS to
indicate to the SCS that it should stop sending data. The SCS will only send data when CTS is asserted.
RTS/CTS is the most reliable method of flow control and is the recommended method for the SCS. In the
event that RTS/CTS flow control cannot be used, XON/XOFF flow control is recommended.
8.11.2 Software Flow Control
XON/XOFF controls the flow of data by sending particular characters through the data stream. The
characters sent to signify the ability or inability to accept data are Ctrl-Q (XON) and Ctrl-S (XOFF).
Applications that use the Ctrl-Q and Ctrl-S characters (such as certain text editors) will conflict with XON/
XOFF flow control. If a user enters a Ctrl-Q or Ctrl-S, these characters won’t be transmitted; they’ll be
interpreted as flow control characters and removed from the data stream.
Protocols that require an 8-bit clean data path cannot use XON/XOFF flow control. Data passes through an
8-bit clean data path unchanged. SLIP requires an 8-bit clean data path; PPP may have the same
requirements if the Asynchronous Character Control Map (ACCM) isn’t set properly. To configure the
ACCM, see Chapter 7,
PPP
.
8.11.3 Setting Up Flow Control
To use flow control on an SCS port, complete the following steps.
1
Set Appropriate Line/Serial Speeds
Consider the line speed and the serial speed of the modem; if data is being compressed, the serial
speed should be higher than the line speed. If you’re connecting a terminal to the port, ensure that the
speed of the terminal matches the port speed.
Note:
See Chapter 9, Modems, for a discussion of line speeds, serial speeds, and data
compression. See your modem’s documentation for information on configuring
the modem’s line and serial speeds.
2
Disable Autobaud
In order to ensure that the set speeds are always used, disable any automatic speed selection or
autobaud options on your modem.
In addition, disable autobaud on the SCS port you’re configuring. To do this, use the
Set/Define Ports
Autobaud
command. This command requires that you be a privileged user.
Figure 8-48:
Disabling Autobaud
Note:
If you aren’t currently a privileged user, use the Set Privileged command.
3
Determine the Appropriate Flow Control Method
Local>> DEFINE PORT 2 AUTOBAUD DISABLED
Содержание SCS
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