
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
ADVANCED CONFIDENTIAL
XRT74L74
REV. P1.1.1
259
When the μP reads these registers, it will read in the
number of parity-bit errors that have been detected by
the Receive DS3 Framer block, since the last time
these registers were read. These registers are reset
upon read.
N
OTE
:
When the Framing with Parity option is selected, the
Receive DS3 Framer block will declared an OOF condition
if P-bit errors were detected in two out of 5 consecutive DS3
M-frames.
5.3.2.6.2
CP-Bit Checking/Options
CP-bits are very similar to P-bits except for the follow-
ing.
1.
CP-bits are used to permit performance monitor-
ing over an entire DS3 path (e.g., from the source
terminal) through any number of mid-network ter-
minals to the sink terminal).
2.
P-bits are used to permit performance monitoring
of a DS3 data stream, as it is transmitted from
one terminal to an adjacent terminal.
How CP-Bits are Processed
The following section describes how the CP-bits are
processed at three locations.
The Source Terminal Equipment
The Mid-Network Terminal Equipment
The Sink Terminal Equipment
Figure_62 presents a simple illustration of the loca-
tions of these three types of Terminal Equipment,
within the Wide-Area Network.
N
OTE
:
The use of the terms Source and Sink Terminal
Equipment are used to simplify this discussion of CP-Bit
Processing. In reality, the Source Terminal Equipment (in
Figure_62) will also function as the Sink Terminal Equip-
ment (for DS3 traffic traveling in the opposite direction).
Likewise, the Sink Terminal Equipment (in Figure_62) will
also function as the Source Terminal Equipment.
Processing at the Source Terminal Equipment
The Source Terminal Equipment (located at one edge
of the wide-area network) will typically receive its DS3
payload data from some Customer Premise Equip-
ment (CPE). As the Source Terminal Equipment re-
ceives this data from the CPE, it will compute the
even-parity value over all bits within a given outbound
DS3 frame. The Terminal Equipment will then insert
this even parity value into both of the P-bit fields and
0
0
0
0
0
0
0
0
PMON PARITY ERROR EVENT COUNT REGISTER - LSB (ADDRESS = 0X55)
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
F
IGURE
89. A S
IMPLE
I
LLUSTRATION
OF
THE
L
OCATIONS
OF
THE
S
OURCE
, M
ID
-N
ETWORK
AND
S
INK
T
ERMINAL
E
QUIPMENT
(
FOR
CP-B
IT
P
ROCESSING
)
Source
Terminal
Equipment
Sink
Terminal
Equipment
Mid-Network
Terminal
Equipment
The Wide Area Network
Customer
Premises
Equipment
Customer
Premises
Equipment