XRT72L13 Datasheet, PDF (362/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

XRT72L13
M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC
REV. P1.0.6
tiplexing data stream, as illustrated below in
Figure 125.
FIGURE 125. THE “ITU-T G.747” PAYLOAD BITS
áç
PRELIMINARY
The 159 or 168 Payload Bits (in each Set)
D1
D2
D3
D1
D2
D3
D1
D2
.
.
.
.
NOTES:
1. D1 denotes that the source of data was from E1 Channel #1
2. D2 denotes that the source of data was from E1 Channel #2
3. D3 denotes that the source of data was from E1 Channel #3
The “ITU-T G.747 FAS (Framing Alignment Signal)
Pattern
The first nine bits, within a given “ITU-T G.747” frame
functions as the Framing Alignment Signal. This nine
bit quantity is assigned the following pattern.
“111010000”
This pattern permits the “Receiving Terminal” to ac-
quire and maintain “ITU-T G.747 Frame Synchroniza-
tion” with the “incoming” G.747 Frames.
The “A” Bit
The “ITU-T G.747” A bit functions as the “Yellow
Alarm” indicator. If a given terminal detects an LOS
(Loss of Signal), AIS or LOF (Loss of Framing) condi-
tion, then that terminal will set the “A” bit (within its
“outbound” G.747 frames) to “1”. The terminal will
continue to set the “A” bit (within each “outbound”
G.747 frame) to “1” for the duration that the defect ex-
ists. The terminal equipment will set the “A” bits
(within its “outbound” G.747 frames) to “0” during
“non-alarm” condition.
The “P” Bit
The “P” bits within a given G.747 frame, represents
the even parity calculation result over the “payload”
bits and “stuff” bits of the previous G.747 frame. This
bit is used to support error detection.
The “CXX” Bits
The “CXX” bits are used to indicate whether bit-stuff-
ing has occurred, when the three E1 signals are be-
ing multiplexed into the G.747 signal. The “C1X” bit
reflects the stuffing status for E1 Channel 1 (when as-
sembling the current G.747 frame).
If “C11” = “C12” = “C13” = 0, then no stuffing was
performed in E1 channel 1. Conversely, if “C11”,
“C12” and “C13” are all “1”, then bit-stuffing was per-
formed in E1 channel 1. Likewise, the “C2X” bits re-
flect the stuffing status for E1 Channel 2 (when as-
sembling the current G.747 frame) and the “C3X” bits
reflect the stuffing status for E1 Channel 3
5.2.1.1.2.2 Additional Roles of the M12 MUX
Block - G.747 Mode
As the M12 MUX block accepts the three (3) E1 sig-
nals and multiplexes these signals into an “ITU-T
G.747” data stream, the M12 MUX block will also do
the following.
• It will insert the “FAS” (Framing Alignment Signal)
into the “outbound” G.747 data stream.
• It will compute the “P” value of a given “G.747”
frame, and will insert the resulting parity value into
the “P” bit-field of the very next “G.747” frame.
• It will insert the necessary “stuff” bits, and will
reflect the “stuff” status within the “CXX” bits, within
each “outbound” DS2 frame.
• If the “companion” M12 DEMUX block (within the
XRT72L13) detects and declares a “RED Alarm”
condition (e.g., an LOS, AIS or LOF condition), then
the M12 MUX will set the “A” bit (within each “out-
bound” G.747 frame) to “1”. This form of signaling
is known as transmitting a “G.747 FERF” indicator
to the remote terminal equipment. The M12 MUX
block will continue to set the “A” bit to “1” for the
duration that this “RED Alarm” condition persists. If
the corresponding M12 DEMUX block does not
detect any “RED Alarm” condition, then the M12
MUX block will set the “A” bit to “0”, which denotes
the normal condition.
350