
XRT7250
DS3/E3 FRAMER IC
á
REV. 1.1.1
198
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.
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.
FIGURE 83. ILLUSTRATION OF THE PRESUMED CONFIGURATION OF THE MID-NETWORK TERMINAL EQUIPMENT
The Receiving
DS3 Line Card
The Receiving
DS3 Line Card
The Transmitting
DS3 Line Card
The Transmitting
DS3 Line Card
System Back-plane
DS3 Traffic
from “Source”
Terminal
Equipment
DS3 Traffic to
“Sink” Terminal
Equipment
The Mid-Network Terminal Equipment