ADC HiGain H2TU-C-202 User Manual page 31

152-202-115-04, Revision 04
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 preprogrammed 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 loopback they
initiate.
The NLOC and NRG1 through NRG2 loopbacks are called tandem DS0 DP loopbacks. They are used to select
one of many loopback points when there are several identical data ports in tandem. The NI loopback is assigned
to the HiGain 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 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 loop-down can also be initiated
by depressing the H2TU-R loopback control button or by any of the standard 3-in-5 loop-down commands. The
implemented detection/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, this 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.
H2TU-C-202 List 1E
are sent in timeslot 1. The S in the Network Code column is a "don't care" bit. The
Table 12. HiGain Loopback vs. Latching Sequence
HiGain Loopback Latching Sequence
NREM 1, 2A, 3, 6
NLOC 1, 2B, 3, 6
NRG1 1, 2B, 3, 4, 5, 6
NRG2 1, 2B, 3, 4, 5, 4, 5, 6
Table 12 is interrupted for more than 20 minutes, the detection is cleared, and
April 21, 2000
Provisioning
-3
bit error rate.
23