35
36
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
), via signals on the serial port interface or the front panel
switch.
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. Toggle the front panel switch to the “Local” position.
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
. 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.
Figure 8.
Local Loopback
Ethernet
Device
Ethernet
Device
Receive
Recover
Clocking
Internal
Clocking
Cable Span
T1/FT1 CSU/DSU
Model 2720/I
T1/FT1 CSU/DSU
Model 2720/I
Clock/
Data
Clock/
Data
Clock/
Data
Data
Data
Model 2720/X
Model 2720/I
LLB Initiated
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).
There are two Remote Loops that can be initiated from the
NetLink-T1 unit: (1) V.54 Loop, and; (2) CSU Loop. The user can
select the type of loop that can be initiated from the
System
Diagnostics/Statistics
screen or with Switch S1-1. When a loopback
is initiated this is the type of loop that the unit uses to loop up the
remote unit. NOTE: The NetLink-T1 will respond to both loops regard-
less of the state of the RDL Type.
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. Set the front panel switch to ‘Remote’.
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.
Figure 9.
Remote Loopback
Ethernet
Device
Ethernet
Device
Receive
Recover
Clocking
Internal
Clocking
Cable Span
T1/FT1 CSU/DSU
Model 2720/I
T1/FT1 CSU/DSU
Model 2720/I
Clock/
Data
Clock/
Data
Clock/
Data
Data
Data
Model 2720/I
RL Initiated
Model 2720/I
x
Summary of Contents for 2720/I Series
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