XRT7245
DS3 UNI FOR ATM
á
PRELIMINARY
REV. 1.03
244
7.2.2.2
Once the Receive PLCP Processor enters into the “In-
frame” mode, the 12 POH bytes are then extracted
and output via a serial output port. Presently, the Re-
ceive PLCP Processor is only concerned with three
(3) of these POH bytes: B1, G1, and C1. The manner
in which the Receive PLCP Processor handles these
POH bytes follows.
Overhead Byte Processing
7.2.2.2.1
The Receive PLCP Processor will perform a BIP-8
calculation over an entire PLCP frame (excluding the
A1, A2 and POI bytes) that it receives from the
Receive DS3 Framer. Afterwards, the Receive PLCP
Processor will read in the B1 byte, of the very next
incoming PLCP frame, and perform a bit-by-bit
comparison between this B1 byte and this locally-
computed BIP-8 value. By the nature of the BIP-8
values, it is possible to have as many as 8 bit errors
B1 (BIP-8) Byte
in this comparison. If the Receive PLCP Processor
detects any BIP-8 errors, then it will do two things:
increment the PMON BIP-8 Error Count Registers
(Address = 28h and 29h) by the number of
detected bit-errors, and,
Inform the “Far-End” Terminal (e.g., the source of
the errored data) of this occurrence by routing the
number of bit-errors that were detected in this
frame to the “Near-End” Transmit PLCP Processor.
The Transmit PLCP Processor will then insert this
number into the FEBE-nibble within the G1 byte of
an outbound PLCP frame. Then the outbound
PLCP frame (containing the information on the B1
byte error) will be transmitted to the “Far-End” ter-
minal where it will be processed appropriately.
Table 53 presents the bit format of the G1 byte. The
Receive PLCP processor performs this function in
order to inform the “Far-End Terminal that bit errors
have been detected in its transmission.
The bit-format of the PMON BIP-8 Error Count Reg-
ister (Address = 28h and 29h) are presented below.
Rx PLCP Configuration/Status Register (Address = 44h)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Unused
Reframe
POOF Status
PLOF Status
Yellow Status
x
x
x
x
1
x
x
x
T
ABLE
53: B
IT
F
ORMAT
OF
THE
G1 B
YTE
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
Far End Block Error (FEBE)
RAI (Yellow)
X bits (Ignored by the Receiver)
4 Bits
1 Bit
3 Bits
Address = 28h, PMON BIP-8 Error 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
BIP-8 Error Count—High Byte
RO
RO
RO
RO
RO
RO
RO
RO
0
0
0
0
0
0
0
0
Address = 29h, PMON BIP-8 Error 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
BIP-8 Error Count—Low Byte
RO
RO
RO
RO
RO
RO
RO
RO