Applications
The following table lists common In-Band loop codes:
Table 3: In-Band loop codes
Device
Loop up code
Loop down code
NIU/Smart Jack
11000
11100
CSU
10000
100
Intelligent repeaters
Vendor-speci
fi
c, typically 16 bits long
Device Loop Points
It is important to know where in a device a loop is occurring. For
example, if a loop device loops the receive signal directly to its transmit
output, then enabling a loop on that device does not test the signal
through the device itself, only the signal that has gotten to the device.
A loop that sends its input signal directly to its output signal, without
passing through the device, is called a front-side loop. In general, NIU
and Smart Jack devices provide front-side loops.
Some CSU devices can provide both a front-side loop and a through (or
payload) loop. A through loop passes through the device, but does not
clear it. For example, a through loop would test the device, but not test
the signal connector hardware at the far side of the device.
Example DS1 Loop Test
NOTE.
A loop test places the line being tested out of service.
This example shows how to set up a DS1 loop from a mobile switching
center (MSC) to a BTS NIU.
1.
Connect the YBT100 DS1 A
RCV
and
XMT
jacks to the DSX
panel
OUT
and
IN
jacks, respectively. Making these connections
takes that line out of service.
NetTek YBT100 and YBT100DS3 Backhaul Tester
27
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