11-4CHAPTER 11: FLOW CONTROL

For your modem to

Command

 

 

Enable Hewlett Packard-Terminal mode. Applies only to

AT&I4

Business Modems attached to terminals in an HP system

 

that uses the ENQ/ACK protocol. Use in ARQ mode only.

 

Enable flow control when the connection is not under

 

error control. For this to work, the remote device must

 

also have AT&I5 capability. In ARQ mode, a Business

 

Modem set to AT&I5 operates the same as it does when

 

set to &I2. It acts on your XON/XOFF commands, but does

 

not pass them to the remote system. The error-control

 

protocol enables the devices to control the flow of data

 

on the phone link.

 

In non-ARQ mode, a Business Modem set to AT&I5

 

operates as though flow control were disabled (AT&I0); it

 

does not look for your typed XON/XOFF commands.

 

However, it does look for XON/XOFF characters coming in

 

over the phone link. When the remote device sends

 

XON/XOFF commands, the Business Modem either

 

resumes or stops transmitting data over the link and drops

 

the characters from the data stream.

 

 

 

If both devices are set to AT&I5, operators at each end can

AT&I5

signal the remote device to stop sending. Thus, controlling

 

the data flow on the phone link and preventing their own

 

device’s buffer from overflowing. At the computer/device

 

interfaces, the devices independently control the flow of

 

data through their Transmit Data (AT&H) settings.

 

 

 

Example: Sending AT&I2 will remove XON/XOFF commands from the data stream instead of sending them to the remote computer. This will force the Business Modem to act of the XON/XOFF commands.

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3Com 56K Enable Hewlett Packard-Terminal mode. Applies only to, AT&I4, Does not look for your typed XON/XOFF commands