XRT7250 datasheet(150/463 Pages) EXAR

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DS3/E3 FRAMER IC

XRT7250

REV. 1.1.1

131

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

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.

XRT7250 Datasheet(PDF) 150 Page - Exar Corporation

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