Csu; Niu4, Niu5; Ntwrk; Line - Fluke 635 User Manual

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Users Manual

2-20. CSU

This selection is made to loop up/down a CSU, typically on the far end of a T1
span (see Chapter 3).

2-21. NIU4, NIU5

This selection is made to loop an NIU. The NIU (sometimes called smart jack)
is part of the network equipment and belongs to the service provider. Most
modern NIUs respond to the NIU5 code. Older NIUs only respond to the NIU4
code.

2-22. NTWRK

This selection is only valid in ESF framing. The NTWRK loop code is
transmitted "out of band" (in the facility data link (FDL) of the ESF signal).
The distant ESF CSU will respond by looping the DS1 signal back at a point
that includes the entire CSU. The NTWRK loop code may be used in
conjunction with the LINE loop code to determine whether a fault exists in the
facility or the CSU. In order to activate the NTWRK loop code, ESF framing
must be selected (using the TX FRAME key).

2-23. LINE

If ESF framing and LINE loop code are selected, pressing the SEND LOOP
UP or SEND LOOP DOWN key will transmit LINE code "out of band" (in
the FDL of the ESF signal). The distant ESF CSU will respond by looping the
entire DS1 signal at a point that does not include the CSU circuitry. The LINE
loop code may be used in conjunction with the NTWRK loop code to
determine whether a fault exists in the facility or the CSU. The LINE loop
code may also be sent in band when D4 framing is selected.

2-24. PYLD

If ESF framing and PYLD loop code are selected, pressing the SEND LOOP
UP or SEND LOOP DOWN key will transmit the PYLD code "out of band"
(in the FDL of the ESF signal). The distant ESF CSU will respond by looping
only the payload (the customer data) of the ESF signal. The FDL will not be
looped back, as with the NTWRK or the LINE loop codes. Because the FDL
isregenerated at the distant CSU, the PYLD loop code is useful in determining
which side of a T1 facility is faulty.
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