![](http://datasheet.mmic.net.cn/Exar-Corporation/XRT79L71IB-F_datasheet_100145/XRT79L71IB-F_443.png)
PRELIMINARY
XRT79L71
428
REV. P2.0.0
1-CHANNEL DS3/E3 CLEAR-CHANNEL FRAMERLIU COMBO - CC/HDLC ARCHITECTURE
Bit 2 within the MA bytes carries the FEBE (Far-End Block Error)/REI (Remote Error Indicator) bit within the
E3, ITU-T G.832 frame. If the Near-End XRT79L71 detects EM byte errors within the incoming (received) E3
data-stream, then it will inform the remote terminal of this fact by setting the FEBE/REI bit-field within the
outgoing, or return E3 frame to the value "1" to indicate an erred condition. The Transmit Section of the
XRT79L71 will set the FEBE/REI bit-field to "0" in order to denote an un-erred condition.
This concept of transmitting the FEBE/REI indicator in response to the detection of EM byte errors is reinforced
in Figures 200 through 203 below.
Figure 200 presents an illustration of a given Near-End Terminal that is exchanging E3 data with the remote
terminal, in an un-erred manner. More specifically, the Receive E3 Framer block has locally computed an EM
byte value of "0x5A" that was computed over a given incoming E3 frame. Figure 200 indicates that the EM
byte value which resides within the very next incoming E3 frame is of the value "0x5A". As a consequence,
there is no EM byte errors being detected at this time.
In response to this un-erred condition, the Transmit E3 Framer within the Near-End Terminal will respond by
setting the FEBE/REI bit-field "0". Figure 201 presents an illustration of the Transmit E3 Framer sending this
un-erred indication to the Remote Terminal Equipment.
FIGURE 200. A SIMPLE ILLUSTRATION OF A NEAR-END TERMINAL EXCHANGING E3 DATA WITH A REMOTE TERMI-
NAL
, IN AN UN-ERRED MANNER
FIGURE 201. A SIMPLE ILLUSTRATION OF THE NEAR-END TERMINAL TRANSMITTING THE UN-ERRED INDICATION TO
THE REMOTE TERMINAL EQUIPMENT
Transmit E3
Framer
Receive E3
Framer
Near-End Terminal
Remote
Terminal
Equipment
Remote
Terminal
Equipment
EM Byte
Locally Calculated
EM Byte
0x5A
Transmit E3
Framer
Receive E3
Framer
Near-End Terminal
Remote
Terminal
Equipment
Remote
Terminal
Equipment
MA Byte
x0xxxxxx
FEBE/REI bit