XRT72L56 Datasheet, PDF (236/486 Pages) Exar Corporation – SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L56 SIX CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.2
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PRELIMINARY
both of the CP-bits fields, within the very next out-
bound DS3 frame.
Hence, both the P-bit values and CP-bit values will
originate at the Source Terminal Equipment.
Processing at the Mid-Network Terminal Equip-
ment
The Mid-Network Terminal Equipment has the task of
doing the following.
• Receiving a DS3 data stream, via the Receive
WAN Interface Line Card.
• Transmitting this same DS3 data stream (out to
another Remote Terminal Equipment) via the Trans-
mit WAN Interface Line Card.
Figure 83 presents an illustration of the basic archi-
tecture of the Mid-Network Terminal Equipment.
FIGURE 83. 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 XRT72L56 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
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