3Com Courier, Reference

Page: 118 / 204

15-6 C
HAPTER
15: T
ESTING THE CONNECTION
Remote Digita
Loopback Testing
(AT&T6, AT&T7)
The remote digital loopback test, verifies the condition of both devices
and of the phone line. Data flow is shown in the figure below.
Data Flow During Remote Digital Loopback.
The request for and granting of remote digital loopback testing requires
that both devices use ITU-T V.22 standard signaling. If the remote device
does not have the capability or is not set to respond (with
AT&T4
), you will
get an ERROR result code.
There are two remote digital loopback options.
Example: Sending
AT&T6
will verify keyboard data sent to the modem by
returning it over the phone lines and displaying it on your screen.
Granting a Digital
Loopback Test
Request (AT&T4)
Using
AT&T4
causes the Courier V.Everything modem to grant a remote
device's request for a remote digital loop-back test.
Canceling All Digital
Loopback Test
Requests (&T5)
Using
AT&T5
cancels
AT&T4
, and the Courier V.Everything modem fails to
acknowledge remote digital loopback test requests. This is the default so
that your Courier V.Everything modem isn't subject to another user
calling and tying up your Courier V.Everything modem without your
permission.
To DTE
Transmitter
Receiver
Telco
To DTE
Transmitter
Receiver
Telco
TX
RX
TX
RX
Local Remote
If you want to Command
Send keyboard data to the modem and verify it when it is
returned over the phone lines and to your screen
AT&T6
Have the modem send its internal test pattern and return
an error count to your screen
AT&T7