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5.2 LOOP (V.54 & TELCO) DIAGNOSTICS
The NetLink-T1™ offers three V.54 loop diagnostics and is com-
patible with two Telco loop diagnostics. Use these diagnostics to test
the CSU/DSU and any communication links. These tests can be acti-
vated via the software control port (See Section
3.2.3 System
Diagnostics) or via signals on the serial port interface.
5.2.1 Operating Local Loopback (LL)
The Local Loopback (LL) test checks the operation of the local
NetLink-T1™, and is performed separately on each unit. Any data sent
to the local NetLink-T1™ in this test mode will be echoed (returned)
back to the user device (i.e., characters typed on the keyboard of a ter-
minal will appear on the terminal screen).
To perform a LL test, follow these steps:
1. Activate LL. This may be done in one of two ways:
a. Enter
Local Loop from the System
Diagnostics/Statistics menu and toggle the <Spacebar>
until “LL” appears next to the Local Loop option.
b. Activate the “LL” signal on the DTE. If you are not sure
which lead is the “LL” signal, please refer to Appendix D.
2. Verify that the data terminal equipment is operating properly
and can be used for a test.
3. Perform a V.52 BER (bit error rate) test as described in
Section 5.3.3. If the BER test equipment indicates no faults,
but the data terminal indicates a fault, follow the manufactur-
er’s checkout procedures for the data terminal. Also, check
the interface cable between the terminal and the NetLink-
T1™.
5.2.2 Operating Remote Digital Loopback (RL)
The Remote Digital Loopback (RL) test checks the performance of
both the local and remote NetLink-T1™, as well as the communication
link between them. Any characters sent to the remote NetLink-T1™ in
this test mode will be returned back to the originating device (i.e, char-
acters typed on the keyboard of the local terminal will appear on the
local terminal screen after having been passed to the remote NetLink-
T1™ and looped back).
a
a
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To perform an RDL test, follow these steps:
1. Activate RDL. This may be done in two ways:
a. Enter
Remote Loop from the System
Diagnostics/Statistics menu and toggle the <Spacebar>
until “RL” appears next to the Remote Loop option.;
b. Activate the “RL” signal on the DTE. If you are not sure
which lead is the “RL” signal, please refer to Appendix D.
2. Perform a bit error rate test (BERT) using the internal V.52
generator (as described in Section 5.3), or using a separate
BER Tester. If the BER test indicates a fault, and the Local
Line Loopback test was successful for both NetLink™s, you
may have a problem with the twisted pair line connection.
5.2.3 Central Office Loops
The NetLink-T1™ also responds to central office initiated loop com-
mands. When in D4 framing mode, the NetLink-T1™ will implement
the “loop up” command when it recognizes the pattern “10000” in the
data stream for a minimum of 5 seconds. The “loop down” command is
implemented by the pattern “100” in the data stream for a minimum of
5 seconds.
When operating in ESF framing mode, loopback commands are
issued via the Facility Data Link (FDL). The line loop message will
cause a loop back before data enters the framer portion of the CSU.
The payload loop message will cause the NetLink-T1™ to loop data
after the framer portion of the CSU.
The NetLink-T1™ will respond to Universal Loopback De-activate
to clear all central office loops.
b
b