XRT74L73 Datasheet, PDF(248/488 Page) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

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XRT74L73 Datasheet, PDF (248/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

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XRT74L73

3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

REV. P1.0.1

PRELIMINARY

FIGURE 89. A SIMPLE ILLUSTRATION OF THE LOCATIONS OF THE SOURCE, MID-NETWORK AND SINK TERMINAL

EQUIPMENT (FOR CP-BIT PROCESSING)

CCuustsotommerer

PPrermemisiesses

EEqquuipipmmenent t

SSouourcrece

TTeremrmininalal

EEqquuipipmmenent t

MMidid-N-Netewtworokrk

TTeremrmininalal

EEqquuipipmmenent t

SSininkk

TTeremrmininalal

EEqquuipipmmenent t

CCuustsotmomerer

PPrermemisiesses

EEqquuipipmmenent t

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_62) will also function as the Sink Terminal Equip-

ment (for DS3 traffic traveling in the opposite direction).

Likewise, the Sink Terminal Equipment (in Figure_62) 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 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.

â¢ Receiving a DS3 data stream, via the Receive

WAN Interface Line Card.

â¢ Transmitting this same DS3 data stream (out to

another Remote Terminal Equipment) via the

Transmit WAN Interface Line Card.

Figure 90 presents an illustration of the basic archi-

tecture of the Mid-Network Terminal Equipment.

249

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