
152-388-115-03, Issue 03
Provisioning
H2TU-C-388 List 1E
April 21, 2000
25
Fractional T1 (FT1) Option.
Fractional T1 circuits can be used in feeder networks to provide frame relay
service. If such circuits are maintained by a DDS test group, then these circuits must respond to DDS/DS0 latching
loopback commands which is the only tool test groups have at their disposal. A latching loopback, once it has been
initiated by the correct sequence, remains locked or latched until the correct loopdown sequence has been
detected.
The FT1 option, when enabled, allows the H2TU-C to respond to DS0 latching loopback commands and thus
support fractional T1 frame-relay applications. This is in addition to the standard full bandwidth T1 2-in-5 loopup
and 3-in-5 loopdown SmartJack commands. FT1 supports both the full T1 commands of ENA and the DDS
latching loopback commands, which must also be enabled. For more information about latching loopback
commands, refer to Bell Core TA-TSY-000077, Issue 3, April 1986.
The FT1 option supports both the DDS NI and DDS DS0 Data Port (DP) latching loopback sequences listed in
The sequences in
above are sent in timeslot 1. The S in the Network Code column is a “don’t care” bit.
The 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
approximately 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.
lists the relationship between the latching loopback sequences and the specific HiGain HDSL2 loopback
they initiate.
Table 11.
DDS NI and DS0 DP Latching Loopback Sequence
Enable Sequence
Minimum
Number of
Bytes
Byte Name
Network Code
1
35
Transition in Progress (TIP)
S 0 1 1 1 0 1 0
2A
35
NI Loop Select Code (LSC)
S 1 0 0 0 0 0 1
2B
35
DS0 DP Loop Select Code (LSC)
S 0 0 0 0 1 0 1
3
100
Loopback Enable Code (LBE)
S 1 0 1 0 1 1 0
4
35
All Ones
S 1 1 1 1 1 1 1
5
100
LBE
S 1 0 1 0 1 1 0
6
32
Far End Voice (FEV)
S 0 1 1 1 0 1 0
Disable/Loopdown
35
TIP
S 0 1 1 1 0 1 0
Table 12.
HiGain HDSL2 Loopback vs. Latching Sequence
HiGain HDSL2 Loopback
Latching Sequence
NREM
1, 2A, 3, 6
NLOC
1, 2B, 3, 6
Содержание H2TU-C-388 HiGain
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