Total Reach Office Channel Unit Data Port Installation and Maintenance Practice
8
61292006L1-5C
False Loopback Immunity
The ADTRAN Protected Loopback family of channel units includes an algorithm compatible
with SARTS
®
, Hekimian
®
, TPI
®
, and other test systems that virtually eliminates false latching
loopbacks. Immunity is automatically enabled at a data rate of 64 kbps. Additionally, the
ADTRAN Protected Loopback family features a
mode for further false
latching loopback protection.
Protected Loopback
The ADTRAN Protected Loopback supports the DDS latching loopback standard in T1E1.2/
99-007R1. When protected loopback is enabled, the TR OCU DP responds to latching
loopback when the idle code preamble is sent prior to the latching loopback sequence
specified in TR62310 and ANSI T1.107. Protected loopback prevents false latching loopbacks
when the loopback sequence is embedded in customer payload data. Test equipment should
support T1E1.2/99-007R1 to perform testing at a data rate of 64 kbps when protected
loopback is enabled. Refer to
for the latching loopback sequence requirement when
protected loopback is enabled.
Note: Minimum of 35 TIP bytes required to disable established latching loopback.
Note: X = Don't care bit
Table 4. Protected Loopback Mode Requirement T1E1.2/99-007R1
(Latching Loopback)
Sequence Function
Byte Code
Number of Received Bytes
Exit data protocol
Idle - 11111110
Minimum of 35 Idle bytes
Clear existing loopbacks
Transition in progress (TIP)
X0111010
Minimum of 35 TIP bytes
Identify device to be looped
Loopback select code (LSC)
X1010101 - OCU
X0110001 - CSU
X1000001 - NEI
Minimum of 35 LSC bytes
Prepare to loop; send MAP code
after 30 bytes
Loopback enabled (LBE)
X1010110
Minimum of 100 LBE bytes
Activate loopback
Far-End voice (FEV)
X1011010
Minimum of 32 FEV bytes
