
Lucent Technologies Inc.
31
Data Sheet
April 1998
T7264 U-Interface 2B1Q Transceiver
Activation and the K2 Interface
(continued)
There is one case in which the LT never receives act = 1
from the NT. If the LT is connected to an NT1, which
has no TE controlling it, the NT can never send act = 1.
T1.601 (Section 6.4.6.6) states that transparency
required to perform loopbacks must be provided
when loopbacks are requested, even when the NT is
not sending act = 1. In this case, the LT, once it has
received oof = 1, must transmit the proper eoc message
to enable the desired remote loopback. The NT1 must
set its xpcy = 0 in response to the eoc loopback
message. Upon receiving the echoed message from
the NT, the LT must set xpcy = 0. Now, transparency is
established over the entire link without having set the
act bits to 1.
Upon receiving act = 1 three consecutive times from
the LT, or upon receiving an eoc loopback message as
discussed above, the NT sets its xpcy = 0, affecting
2B+D transparency in the upstream direction over the
entire link. Prior to this, the NT transceiver was inter-
nally overwriting the upstream 2B+D data to all 1s per
T1.601. The link is now fully operational.
Table 23. Definitions of Signals During Start-Up
* Tones have alternating pattern of four +3s, followed by four –3s, and no SW.
See Figure 21 for start and/or stop time of this signal.
Signals SN3 and SL3 continue indefinitely (or until deactivation).
Notes:
TN, TL
—
Tones produced by NT or LT, respectively.
SNx, SLx —
Pulse patterns produced by NT or LT, respectively.
Tx
—
Notation refers to transition instants defined in Figure 21.
Absent
—
Under superframe, this notation means that only SW is transmitted, not ISW.
Normal
—
Normal means that the M bits are transmitted onto the 2-wire line as required during normal operation (e.g., valid crc bits, eoc
bits, and indicator bits are transmitted).
Normal+
—
Except to perform a loopback, 2B+D bits remain in the previous state (SN2 or SL2) until both act bits indicate full transparency
of the B- and D-channels (i.e., the 2B+D bits of SN3 and SL3 must remain set to 1 and 0, respectively, until transparency is
achieved at both ends of the DSL).
Priority
Priorities exist for responding to several signals as follows:
1. RESET
2. afrst
3. ILOSS
4. tone detection
5. istp
6. lpbk
Signal
Sync Word
(SW)
±
3*
Present
Present
Present
Superframe
(ISW)
±
3*
Absent
Absent
Present
2B+D
M
Start
Stop
Time
(Frames)
TN
±
3*
1
1
±
3*
1
1
6
SN1
SN2
SN3
T1
T5
T6
T2
T6
—
—
—
Normal
+
±
3*
1
0
Normal
TL
SL1
SL2
SL3
±
3*
±
3*
±
3*
1
2
—
—
—
Present
Present
Present
Absent
Present
Present
T3
T4
T7
T4
T7
Normal
Normal
Normal