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XRT79L71
PRELIMINARY
325
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
REV. P2.0.0
If the Transmit DS3/E3 Framer block is configured to support the E3, ITU-T G.751 framing format, then it can
be capable of transmitting the FEBE/REI indicator to the remote terminal equipment.
If the Transmit DS3/E3 Framer block is configured to support the transmission of the FEBE/REI indicator to the
remote terminal equipment, then the purpose of this indication is two-fold.
1.
It permits a Terminal (which is transmitting an E3 data-stream to the remote terminal) to determine
whether or not this remote terminal is receiving its E3 data, in an error-free manner.
2.
It permits a Terminal (which is receiving an E3 data-stream from a remote terminal) to inform this remote
terminal when it is receiving "erred" E3 frames.
A NOTE ABOUT TRANSPORTING THE FEBE/REI INDICATOR VIA THE A-BIT
If the Transmit DS3/E3 Framer block is configured to transmit the FEBE/REI indicator, then the following
conditions/restrictions apply.
1.
If the Transmit DS3/E3 Framer block is configured to support the transmission of the FEBE/REI indicator,
then it WILL NOT support the transmission of the FERF/RDI indicator.
2.
The Transmit DS3/E3 Framer block will only support the transmission of the FEBE/REI indicator, if it (and
the corresponding Receive DS3/E3 Framer block) has been configured to support the computation/
insertion and verification of the BIP-4 value within each E3 frame.
The role of the "A" bit-field (within the E3 frame, when configured to carry the "FEBE/REI" indicator) is best
presented in the practical example below.
Example:
Consider a "Near-End" terminal that is communicating with a remote terminal.
This "Near-End" terminal
consists of the "Transmit DS3/E3 Framer" block and the "Receive DS3/E3 Framer" block within the XRT79L71,
The "Transmit DS3/E3 Framer" block will generate and transmit E3 frames to the remote terminal. Likewise,
the "Receive DS3/E3 Framer" block will receive and process E3 frames, originating from the remote terminal.
The "Near-End" Receive DS3/E3 Framer block (e.g., the Receive DS3/E3 Framer block within this particular
device) is going to verify the values of the BIP-4 nibble within the incoming E3 frames (from the remote
terminal equipment). If the "Near-End" Receive DS3/E3 Framer block detects no BIP-4 errors in the incoming
E3 frame, then it will notify the remote terminal of this fact by forcing the "Near-End" Transmit DS3/E3 Framer
block, to set the "A" bit, within the very next "outbound" E3 frame (which is destined for the remote terminal) to
Figures _ illustrates the "Near-End" Receive DS3/E3 Framer block receiving a "error-free" E3 frame. In this
figure, the Receive DS3/E3 Framer block has locally computed a BIP-4 value of "0x0A" (that was computed
over a given incoming E3 frame). Figure 148 indicates that the BIP-4 nibble value (which resides within the
very next incoming E3 frame) is of the value "0x0A". As a consequence there is no BIP-4 nibble error being
detected at this time.