AT&T 7400B Plus User Manual page 174

APPENDIX D: LOOPBACK DATA TESTS
Page D-2
Terminal
or Modem
PC
Figure B Using the Loopback Data Test Arrangement with Modem Pooling
The Loopback Data Test Arrangement is also useful for isolating problems in networks of
digitally connected switches. The scenario is a user at one site needing to access a host at another
site and having problems. The user is instructed by the Help Desk to call the local Loopback Data
Test Arrangement. If this succeeds, the problem is isolated to the network or to the remote host
equipment. The user is then instructed to call a Loopback Data Test Arrangement at the host site
(see Figure C). If this call succeeds than the problem is not in the network between the switches.
Terminal RS
or
PC 232
Figure C Using the Loopback Data Test Arrangement in a Network
NETWORK
Data Module
PC/PBX,
or
ADU
DEFINITY Communications System
Modem Pool
System 75
System 85
DEFINITY
Data Module
ADU
System 75 System 75
System 85 System 85
DEFINITY DEFINITY
7400B Plus Data Module
User´s Guide
DCP
7400B Plus
Loopback
Host
or
DCP
7400B Plus
Loopback
Plug
Host
Plug