700-701-100-02

Functional Description

 

 

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)

Table 13.

Loopback Equivalents

 

 

 

 

 

Console Screen Test Menu

Front Panel

 

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.

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.

The BER test must be stopped before leaving the test menu to restore normal payload transmission. Typing ESC while the BER test is in progress causes the

following message to display: “BER Test in Progress. Must STOP before leaving screen.”

UTU-701 and ETU-751 List 1

August 9, 2002

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