XRT72L50 Datasheet, PDF (216/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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FIGURE 70. A SIMPLE ILLUSTRATION OF THE LOCATIONS OF THE SOURCE, MID-NETWORK AND SINK TERMINAL
EQUIPMENT (FOR CP-BIT PROCESSING)
CCuustsotommerer
PPrermemisiesses
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SSouourcrece
TTeremrmininaal _l
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MMidid-N-Netewtworokrk
TTeremrmininalal
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SSininkk
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CCuustsotmomerer
PPrermemisiesses
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The Wide Area Network
NOTE: 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 70) will also function as the Sink Terminal
Equipment (for DS3 traffic traveling in the opposite direction). Likewise, the Sink Terminal Equipment 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 Equipment (CPE). As the Source Terminal Equipment receives
this data from the CPE, it will compute the even-parity value over all the payload 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 outbound 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 Equipment
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 71 presents an illustration of the basic architecture of the Mid-Network Terminal Equipment.
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