XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
228
7.1.2.4
Performance Monitoring of the DS3
Transport Medium
The DS3 Frame consists of some overhead bits that
are used to support performance monitoring of the
DS3 Transmission Link. These bits are the P-Bits and
the CP-Bits.
7.1.2.4.1
The “Far-End” Transmit DS3 Framer will compute the
even parity of the payload portion of a DS3 Frame
and will place the resulting parity bit value in the 2
P-bit-fields within the very next “outbound” DS3
Frame. The value of these two bits fields are expected
to be identical.
The Receive DS3 Framer, while receiving each of
these DS3 Frames (from the “Far-End” Transmit DS3
Framer), will compute the even-parity of the payload
portion of the frame. The Receive DS3 Framer will
P-Bit Checking/Options
then compare this “l(fā)ocally computed” parity value to
that of the P-bit fields within the very next DS3
Frame. If the Receive DS3 Framer detects a parity
error, then three things will happen:
The Receive DS3 Framer will inform the local μP/
μC of this occurrence by generating a “Detection
of P-Bit Error” interrupt;
The Receive DS3 Framer will alter the value of
the FEBE bits, (to a pattern other than “111”) that
the “Near-End” Transmit DS3 Framer will be
transmitting back to the “Far-End” Terminal.
The PMON Parity Error Event Count Registers
(Address = 24h and 25h) will be incremented for
each detected parity error, in the incoming DS3
data stream. The bit-format of these two regis-
ters follows.
1.
2.
3.
When the local μP reads these registers, it will read
in the number of parity-bit errors that have been de-
tected by the Receive DS3 Framer, since the last
time these registers were read. These registers are
reset upon read.
Note:
When the “Framing with Parity” option is selected,
the Receive DS3 Framer will declared an “OOF” condition if
P-bit errors were detected in two out of 5 consecutive DS3
M-frames.
Rx DS3 Interrupt Status Register (Address = 11h)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
CP Bit RUR
Error
Interrupt
Status
LOS
Interrupt
Status
AIS Interrupt
Status
IDLE
Interrupt
Status
FERF
Interrupt
Status
AIC
Interrupt
Status
OOF
Interrupt
Status
Parity Error
Interrupt
Status
RO
RUR
RUR
RUR
RUR
RUR
RUR
RUR
0
x
x
x
1
x
x
x
Address = 24h, PMON Parity Error Event Count Register—MSB
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Parity Error Count—High Byte
RO
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
0
0
Address = 25h, PMON Parity Error Event Count Register—LSB
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Parity Error Count—Low Byte
RO
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
0
0