Datasheet
DS26521 Single T1/E1/J1 Transceiver
74 of 258
Figure 8-20. Typical Monitor Application
PRIMARY
T1/E1 TERMINATING
DEVICE
MONITOR
PORT JACK
T1/E1 LINE
X
F
M
R
DS26521
Rt
Rm
Rm
SECONDARY T1/E1
TERMINATING
DEVICE
8.11.3.4 Loss of Signal (LOS)
The DS26521 uses both the digital and analog loss-detection method in compliance with the latest ANSI T1.231 for
T1/J1 and ITU-T G.775, or ETS 300 233 for E1 mode of operation.
Loss of signal (LOS) is detected if the receiver level falls below a threshold analog voltage for certain duration.
Alternatively, this can be termed as having received “0s” for a certain duration. The signal level and timing duration
are defined in accordance with the ANSI T1.231, ITU-T G.775, or ETS 300 233 specifications.
For short-haul mode, the loss-detection thresholds are based on cable loss of 12dB to 18dB for both T1/J1 and E1
modes. The loss thresholds are selectable based on
Table 9-19. For long-haul mode, the LOS detection threshold
is based on cable loss of 30dB to 38dB for T1/J1 and 30dB to 45dB for E1 mode. Note there is no explicit bit called
short-haul mode selection. Loss declaration level is set at 3dB lower that the maximum sensitivity setting
programmed in
Table 9-19.
The loss state is exited when the receiver detects a certain ones density at the maximum sensitivity level or higher,
which is 3dB higher than the loss-detection level. The loss-detection signal level and loss-reset signal level are
defined with hysteresis to prevent the receiver from bouncing between “LOS” and “no LOS” states.
Table 8-33
outlines the specifications governing the loss function.
Table 8-33. ANSI T1.231, ITU-T G.775, and ETS 300 233 Loss Criteria Specifications
STANDARD
CRITERIA
ANSI T1.231 ITU-T G.775 ETS 300 233
Loss
Detection
No pulses are detected for 175
±75 bits.
No pulses are detected for
duration of 10 to 255-bit
periods.
No pulses are detected for a
duration of 2048-bit periods or
1ms.
Loss Reset
Loss is terminated if a duration
of 12.5% ones are detected
over duration of 175 ±75 bits.
Loss is not terminated if 8
consecutive zeros are found if
B8ZS encoding is used. If
B8ZS is not used, loss is not
terminated if 100 consecutive
pulses are zero.
The incoming signal has
transitions for duration of 10 to
255-bit periods.
Loss reset criteria are not
defined.