XRT74L73 Datasheet, PDF (249/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
FIGURE 90. ILLUSTRATION OF THE PRESUMED CONFIGURATION OF THE MID-NETWORK TERMINAL EQUIPMENT
System Back-plane
DS3 Traffic
from “Source”
Terminal
Equipment
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DS3 Traffic to
“Sink” Terminal
Equipment
The Mid-Network Terminal Equipment
Operation of the Receive WAN Interface Line Card
The Receive WAN Interface line card receives a DS3
data stream from some remote Terminal Equipment.
As the Receive WAN Interface card does this, it will
also do the following:
1. Compute and verify the “P-Bits” of each inbound
DS3 frame.
2. Compute and verify the “CP-Bits” of each
inbound DS3 frame.
3. Output both the payload and overhead bits to the
system back-plane.
Operation of the Transmit WAN Interface Line
Card
The Transmit WAN Interface Line Card receives the
outbound DS3 data stream from the system back-
plane. As the Transmit WAN Interface Line Card re-
ceives this data it will also do the following.
1. Extract out the “CP-bit” values, from the Receive
WAN Interface line card (via the system back-
plane) and insert these values into the CP-bit
fields, within the outbound DS3 data stream, via
the Transmit Overhead Data Input Interface block
of the XRT74L73 Framer IC.
2. Compute the even-parity over all bits, within a
given outbound DS3 frame, and insert this value
into the “P” bits within the very next outbound
DS3 frame.
3. Transmit this resulting DS3 data stream to the
remote terminal equipment.
Processing at the Sink Terminal
The Sink Terminal Equipment (located at the opposite
edge of the wide-area-network, from the Source Ter-
minal Equipment) will receive and terminate this DS3
data stream. As the Sink Terminal Equipment re-
ceives this DS3 data stream it will also do the follow-
ing.
1. Compute and verify the “P”-bits within each
inbound DS3 frame.
2. Compute and verify the “CP” bits within each
inbound DS3 frame.
4.3.3 The Receive HDLC Controller Block
The Receive DS3 HDLC Controller block can be used
to receive either bit-oriented signaling (BOS) or mes-
sage-oriented signaling (MOS) type data link mes-
sages. The Receive DS3 HDLC Controller block can
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