XRT7250 Datasheet, PDF (217/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

XRT7250 DS3/E3 FRAMER IC
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REV. 1.1.1
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
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
Transmit 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 XRT7250 Framer IC.
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