Appendix D: Loopback Data Tests; Loopback Data Test - AT&T 7400B Plus User Manual

DEFINITY Communications System
7400B Plus Data Module
User´s Guide

APPENDIX D: LOOPBACK DATA TESTS

LOOPBACK DATA TEST

Terminal
RS232
or
PC
If the user is successful in connecting to the Test Arrangement (the data typed in is echoing back)
then be assured that the user's desktop equipment and connection through the switch are
functioning correctly. Help Desk personnel can than look elsewhere for the problem, saving
valuable time in trouble isolation.
A Loopback Data Test Arrangement can also be useful for modem pool calls. An off-premises
user having trouble connecting to a host can call the Loopback Data Test Arrangement (see
Figure B). Again, if the call succeeds, the problem is not in the modem pool.
This appendix provides information on how to perform loopback
tests and how to isolate problems using the 7400B Plus.
The 7400B Plus Loopback Data Test Arrangement provides a
simple mechanism for isolating problems. In the Loopback Data
Test Arrangement one or more 7400B Plus are set up for auto
answer, and have the received data lead looped back to the
transmit data lead on the data module's EIA interface. A user can
then dial up the Loopback Data Test Arrangement and see if the
data typed in at the local station is echoed back. A typical use for
this would be a user who calls the Help Desk with the complaint
that they can not access a local host. The user can be instructed to
call the Loopback Data Test Arrangement (see Figure A).
Data Module,
PC/PBX,
or
ADU
Figure A Local Loopback Data Test Arrangement
APPENDIX D: LOOPBACK DATA TESTS
Digital
System 75
Communications
System 85
Protocol
DEFINITY
Data Module
or ADU
Page D-1
7400B Plus
Loopback
Plug
Host