There are two Remote Loops that can be initiated from the
NetLink 2701/I unit: (1) V.54 Loop, and; (2) CSU Loop. The user can
select the type of loop that can be initiated by Switch S2-4. When a
loopback is initiated this is the type of loop that the unit uses to loop up
the remote unit and which type of loop the unit will respond to.
To perform an RDL test, follow these steps:
1. Activate RDL. This may be done by setting the front panel
switch to ‘Remote’.
2. Perform a bit error rate test (BERT) using the internal V.52
generator (as described in Section 6.2.4), 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.
6.2.3 CSU Loop
Although CSU Loop is predominantly a T1 function, the NetLink-
2701/I responds to central office initiated loop commands. Customers
can use this facility when the Central Office network switch supports
CSU loops over an E1 interface.
When CSU Loop is selected, and when in D4 framing mode, the
NetLink 2701/I will implement the “loop up” command when it recog-
nizes the pattern “10000” in the data stream for a minimum of 5 sec-
onds. The “loop down” command is implemented by the pattern “100”
in the data stream for a minimum of 5 seconds.
The NetLink 2701/I will respond to Universal Loopback De-activate
to clear all central office loops.
6.2.4 Using the V.52 (BER) Test Pattern Generator
To use the V.52 BER tests in conjunction with the Remote Digital
Loopback tests (or with Local Line Loopback tests), follow these
instructions:
1.
Locate the “511/511E” toggle switch on the front panel of the
2701/I and move it UP. This activates the V.52 BER test mode
and transmits a “511” test pattern into the loop. If any errors
are present, the local modem’s red “ER” LED will blink sporad
ically.
2.
If the above test indicates no errors are present, move the
V.52 toggle switch DOWN, activating the “511/E” test with
errors present. If the test is working properly, the local
modem's red “ER” LED will blink once per second. A suc-
cessful “511/E” test will confirm that the link is in place, and
that the Model 2701/I’s built-in “511” generator and detector
are working properly.
NOTE: The above V.52 BER tests can be used independently
of the Remote Digital Loopback tests. This requires two oper-
ators: one to initiate and monitor the tests at the local Model
2701/I, and one to do the same at the remote Model 2701/I.
In this case, the test pattern sent by each Model 2701/I will
not be looped back, but will be transmitted down the line to
the other Model 2701/I. While one operator initiates test, the
other monitors for errors.
Figure 13. Remote Loop in a Network Extension Application
Ethernet
Device
Ethernet
Device
Model 2701/I
Receive
Recover
Clocking
Internal
Clocking
Cable Span
G.703/G.704 NTU
Model 2701/I
G.703/G.704 NTU
Model 2701/I
Clock/
Data
Clock/
Data
Clock/
Data
Data
Data
Model 2701/I
19
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