XRT74L74 Datasheet, PDF (361/498 Pages) Exar Corporation – 4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

PRELIMINARY
XRT74L74
4 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.1.1
FIGURE 146. THE LOCAL RECEIVE E3 FRAMER BLOCK, TRANSMITTING AN E3 FRAME TO THE REMOTE TERMINAL
WITH THE “A” BIT SET TO “0”
Local Terminal
Value = 0
Transmit E3
Framer
Receive E3
Framer
A Bit
Remote
Terminal
However, if the locally computed BIP-4 value does
not match the BIP-4 value of the corresponding E3
frame, then the Receive E3 Framer block will do the
following.
• It will inform the Remote Terminal of this fact by
having the Local Transmit E3 Framer block send
the Remote Terminal an E3 frame, with the “A” bit-
field set to “1”. This phenomenon is illustrated
below in Figure 147 and Figure 148 .
Figure 147 illustrates the Local Receive E3 Framer
receiving an errored E3 frame. In this figure, the Lo-
cal Receive E3 Frame block is receiving an E3 frame
with an BIP-4 containing the value “0xA”. This value
does not match the locally computed BIP-4 value of
“0xB”. Consequently, there is an error in the previous
E3 frame.
Figure 148 illustrates the subsequent action of the
Local Transmit E3 Framer block, which will transmit
an E3 frame, with the A bit-field set to “1” to the Re-
mote Terminal. This signaling indicates that the Local
Receive E3 Framer block has received an errored E3
frame.
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