5.3.3 Telco Testing
The digital service provider’s central office can perform CSU
diagnostic testing. These diagnostics allow the central office to evalu-
ate the circuit operation without making visits to the customer’s premis-
es.
CSU Loop
The CSU loop is activated when the central office reverses the DC
sealing current that flows between the Transmit (TX) and Receive (RX)
pairs. The Model 2530 recognizes this and loops the signals on the
RX pairs back to the central office on the TX pair. While the CSU loop
is activated, the TM light is illuminated.
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5.4 BIT ERROR RATE (V.52) DIAGNOSTICS
The Model 2530 offers two V.52 Bit Error Rate (BER) test patterns.
These test patterns may be invoked along with the LAL and RDL tests
to evaluate the unit(s) and the communication links.
When a 511 or 2047 test is invoked, the 2530 generates a pseu-
do-random pattern of 511 bits (or 2047 bits) using a mathematical poly-
nomial. The receiving Model 2530 then decodes the received bits
using the same polynomial. If the received bits match the agreed upon
pseudo-random pattern, then the 2530(s) and the communication
link(s) are functioning properly.
511
Initiates a built-in 511 bit pseudo-random
pattern generator and detector.
511 with Errors
Initiates a built-in 511 bit pseudo-random
pattern generator and detector. The test
pattern generator also injects
intentional
errors approximately twice per second,
causing the Error LED to blink.
2047
Initiates a built-in 2047 bit pseudo-random
pattern generator and detector.
2047 with Errors
Initiates a built-in 2047 bit pseudo-random
pattern generator and detector. The test
pattern generator also injects
intentional
errors approximately twice per second,
causing the Error LED to blink.
To perform a V.52 BER test, follow these steps:
1.
Select the 511 or 2047 test pattern using Switch 3-1.
1.
Locate the “Pattern” toggle switch on the front panel of the
2530 and move it DOWN to “Normal. This activates the V.52
transmission and reception of the selected test pattern. If
there are errors in the received pattern, the error LED will
blink accordingly.
2.
If the above test indicates no errors are present, move the
toggle switch UP to “Errored”, activating the BER test with
intentional errors. If the test is working properly, the local
modem's red error LED blink approximatley twice per second.
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CSU
DSU
Digital Network
Figure 7. CSU loop
