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700-701-100-02 Functional Description
UTU-701 and ETU-751 List 1 August 9, 2002 21
Table 13 summarizes the equivalent loopbacks for two different activation methods:
• LTU and NTU LOC and REM buttons
• console screen Test menus (see “Testing” on page 60 for loopback operation from the Test menus)
BER TESTING
The HDSL units provide a mechanism for validating circuit integrity utilizing a pseudorandom bit sequence
(PRBS) generator and BER meter internal to the LTU unit. This diagnostic test disrupts the normal flow of
payload traffic, and requires the presence of a Network NTU-I/F loopback or an external physical loopback at the
NTU interface connector. The test is run at the selected HDSL Payload Rate (see Table 18 on page 38). BER
results are accumulated continuously and updated on the console screen at intervals of approximately 16 seconds.
The PRBS data pattern is always generated at the LTU toward the HDSL channel, and the BER is always
measured at the LTU based on data received from the HDSL channel. The test may be initiated and stopped from
the Test menu at either the LTU or NTU console screen.
Table 13. Loopback Equivalents
Front Panel
Console Screen Test Menu
Loopback mode Loopback Position
LTU LOC button NETWORK
(a)
LTU-HDSL
LTU REM button NETWORK NTU-I/F
NETWORK LTU-I/F
NTU LOC button CUSTOMER
(b)
NTU-HDSL
NTU REM button CUSTOMER LTU-I/F
CUSTOMER NTU-I/F
(a) Activated from console screen Test menu at LTU.
(b) Activated from console screen Test menu at NTU.
The BER test must be stopped before leaving the test menu to restore normal
payload transmission. Typing
while the BER test is in progress causes the
following message to display:
“BER Test in Progress. Must STOP
before leaving screen.”
ESC