Higain Hdsl2 Loopback Vs. Latching Sequence - ADC HiGain H2TU-C-388 Technical Practice

Provisioning
The sequences in Table 11
loopback is activated after the detection of Sequence 6. Upon completion of the enable sequence, the Test Center
continues to transmit FEV bytes in multiples of 20 until FEV confirmation bytes are returned, or until about 2
seconds have elapsed. If the confirmation bytes are not received, a failed attempt is reported. Anticipate the
minimum number of bytes when the loopback code is transmitted by a pre-programmed machine test pattern
generator. These minimum number of bytes will most likely be exceeded when the codes are sent manually. Also,
manual testing may inject random data signals between valid control sequences. The detection algorithm ignores
these occurrences and only responds to valid control codes.
Table 12 lists the relationship between the latching loopback sequences and the specific HiGain HDSL2 loopback
they initiate.
The NLOC loopback is called a tandem DS0 DP loopback. It is used to select one of many loopback points when
there are several identical data ports in tandem. The NI loopback is assigned to the H2TU-R (NREM) since it is
usually located at the Network Interface (NI). The DS0 DP tandem loopback is assigned to the rest of the HiGain
HDSL2 loopbacks because most DDS test sets support this tandem command set.
The Test Center transmits a group of 40 TIP bytes to loop down the loopback. It continues to transmit TIP bytes
in multiples of 20 until the TIP bytes are not returned or until about 2 seconds have elapsed. If the bytes are absent,
a successful loopdown is reported; otherwise, a failed loopdown is reported. The loopdown can also be initiated
by depressing the H2TU-R loopback control button or by any of the standard 3-in-5 loopdown commands. The
implemented detection or release loopback algorithm functions properly in the presence of a 10
Since the FT1 mode is a combination of both the full T1 and the latching loopback modes, all codes are always
active. Therefore, if a loopback is initiated by a latching sequence, it can be looped down by either a latching or
generic loopback and vice versa. All loopback commands are completely symmetric in the FT1 mode.
If the latching sequence shown in
the H2TU-C reverts back to its initial state where it searches for the initial sequence 1.
After a successful latching sequence terminates in a latched loopback state, the state remains until the Disable
command is detected, or until the LBTO option of NONE, 20, 60, or 120 minutes has expired, whichever occurs
first.
The unframed AIS pattern that is normally sent towards the network for a CI LOS fault condition must be replaced
by the new patterns listed in
26
are sent in timeslot 1. The S in the Network Code column is a "don't care" bit. The
Table 12. HiGain HDSL2 Loopback vs. Latching Sequence
HiGain HDSL2 Loopback
NREM
NLOC
Table 12 is interrupted for more than 20 minutes, the detection is cleared, and
Table 13 on page 27
February 28, 2001
Latching Sequence
1, 2A, 3, 6
1, 2B, 3, 6
when the FT1 loopback option is selected.
LTPH-TP-1001-02, Issue 2
-3
bit error rate.
H2TU-C-388 List 3E