XRT72L13 Datasheet, PDF (68/370 Pages) Exar Corporation – M13 MULTIPLEXER/CLEAR CHANNEL DS3 FRAMER IC

XRT72L13 MULTIPLEXER/FRAMER IC
REV. 1.0.6
• Set the “X” bits (within each “outbound” DS2 frame)
to the appropriate value in order to reflect the “DS2
FERF” indicator when conditions warrant.
The XRT72L13 will accept up to 28 DS1 lines or up to
21 E1 lines as inputs to the M12 Multiplexer. Associ-
ated with each of these DS1 or E1 lines is an input
clock signal that the device will use to sample and
latch into the device.
In all, the M12 MUX is capable of MUXing 28 DS1
lines into 7 DS2 lines. Additionally, the M12 MUX is
also capable of MUXing 21 E1 lines into 7 ITU-T
G.747 lines.
1.1.1.2 Operation of the M23 MUX
The M23 MUX, within the XRT72L13 will accept up to
7 DS2 or ITU-T G.747 data streams and will MUX
these signals into a DS3 data stream. Afterwards,
this DS3 data stream will be routed to the "Clear
Channel DS3 Framer" block for further processing.
1.1.1.3 Operation of the "Clear Channel DS3
Framer Block"
Once this data is routed to the "Clear Channel DS3
Framer Block", the DS3 data stream will be encapsu-
lated into a "outbound" DS3 framing structure, and
will be transmitted to an off-chip LIU IC. The Clear
Channel DS3 Framer Block is also responsible for a
variety of other necessary function, such as:
• Transmission of PMDL (Path Maintenance Data
Link) Messages
• Transmission of FEAC (Far-End Alarm & Control)
Messages
• Transmission of the FERF (Far-End Receive Fail-
ure) Indicator
• Transmission of the FEBE (Far-End Block Error)
Indicator
• Computation of P and CP-Bits
1.1.2 In the Receive Direction
When the XRT72L13 is operating in the "Multiplexer/
De-Multiplexer" Mode, the data (in the "Receive Di-
rection") passes through the following block.
• The Clear Channel DS3 Framer Block
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PRELIMINARY
• An M23 DEMUX
• An M12 DEMUX
1.1.2.1 Operation of the Clear Channel DS3
Framer Block
The purpose of the "Clear Channel DS3 Framer
Block" is to perform the following functions:
• To verify the P and CP-bits.
• To Terminate the PMDL Messages.
• To Terminate the FEAC Messages
• To Terminate and interpret the FERF Indicator
• To Terminate and interpret the FEBE Indicator.
• To strip off the "Overhead" bytes and route the pay-
load portion of the "inbound" DS3 frame to the M23
DEMUX
1.1.2.2 Operation of the M23 DEMUX
The purpose of the M23 DEMUX, within the
XRT72L13 is to accept this DS3 data stream and de-
multiplex either 7 DS2 or ITU-T G.747 data streams.
Afterwards, these data streams will be routed to the
M12 DEMUX.
1.1.2.3 Operation of the M12 DEMUX
The purpose of the M12 DEMUX, within the
XRT72L13 is to accept either the 7 DS2 or ITU-T
G.747 data streams and to de-multiplex up to 28 DS1
signals or up to 21 E1 signals.
1.1.3 Diagnostic Resources available for MUX/
DEMUX Mode
In all, the XRT72L13 supports two types of loop-back
modes, while it is configured to operate in the "MUX/
DEMUX" Mode.
• DS1/E1 Tributary Loop-Back
• DS2/ITU-T G.747 Tributary Loop-Back
Each of these Loop-Back Modes are briefly dis-
cussed below.
1.1.3.1 DS1/E1 Tributary Loop-Back
Figure 27 presents an illustration of the XRT72L13
operating in the "DS1/E1 Tributary Loop-Back Mode.
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