XRT7250 Datasheet, PDF (150/463 Pages) Exar Corporation – DS3/E3 FRAMER IC

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DS3/E3 FRAMER IC
XRT7250
three FEBE bits (within an outgoing DS3 Frame) to
any pattern other than "111" to indicate an error. The
Transmit Section will then transmit this information
out to the Remote Terminal (e.g., the source of the er-
rored-data). The FEBE bits, in the outbound DS3
frames, are set to "111" only if both of the following
conditions are true:
• The Receive DS3 Framer has detected no M-bit or
F-bit framing errors, and
• No P-Bit parity errors have been detected.
• No CP-Bit errors have been detected.
NOTE: A more detailed discussion on the Transmit Sec-
tion's handling of the FEBE bit-fields can be found in Sec-
tion 3.2.4.2.1.9.
The Yellow Alarm or FERF (Far-End Receive Fail-
ure) Indicator
The X-bits are used for sending Yellow Alarms or the
FERF (Far-End Receive Failure) indication. When
the Receive Section (of the XRT7250), within the Re-
mote Receiving terminal equipment, cannot identify
valid framing, or detects an AIS pattern in the incom-
ing DS3 data-stream, the Framer IC can be config-
ured such that the Transmit Section will send a Yellow
Alarm or a FERF (Far-End Receive Failure) indication
to the Remote Terminal by setting both of the X-bits to
zero in the outbound (returning) DS3 path. The X-
bits are set to "1" during non-alarm conditions.
4.1.4 The Data Link Related Overhead Bits
REV. 1.1.1
UDL: User Data Link (C-bit Parity Frame Format
Only)
These bit-fields are not used by the framer and are
set to "1" by default. However, these bits may be
used for the transmission of data via a proprietary da-
ta link. The user can access these bit-fields via the
Transmit Overhead Data Input Interface and the Re-
ceive Overhead Data Output Interface blocks.
DL: Path Maintenance Data Link (C-bit Parity
Frame Format Only)
The LAPD transceiver block uses these bit-fields for
the transmission and reception of path maintenance
data link (PMDL) messages via ITU-T Q.921 (LAP-D)
Message frames. Please see Sections 3.2.3.2 and
3.3.3.2 for more information on the operation and
function of the LAPD Transmitter.
4.2 THE TRANSMIT SECTION OF THE XRT7250 (DS3
MODE OPERATION)
When the XRT7250 has been configured to operate
in the DS3 Mode, the Transmit Section of the
XRT7250 consists of the following functional blocks.
• Transmit Payload Data Input Interface block
• Transmit Overhead Data Input Interface block
• Transmit DS3 Framer block
• Transmit DS3 HDLC Controller block
• Transmit LIU Interface block
Figure 42 presents a simple illustration of the Trans-
mit Section of the XRT7250 Framer IC.
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