XRT86VL3X datasheet(34/154 Pages) EXAR

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XRT86VL3X

T1/E1/J1 FRAMER/LIU COMBO - ARCHITECTURE DESCRIPTION

REV. 1.2.3

3.8.2

Periodic Performance Report

The ANSI T1.403 standard requires that the status of the transmission quality be reported in one-second

intervals. The one-second timing may be derived from the DS1 signal or from a separate equally accurate

(±32ppm) source. The phase of the one-second periods does not depend on the time of occurrence of any

error event. A total of four seconds of information is transmitted so that recovery operations may be initiated in

case an error corrupts a message. Counts of events shall be accumulated in each contiguous one-second

interval. At the end of each one-second interval, a modulo-4 counter shall be incremented, and the appropriate

performance bits shall be set in bytes 5 and 6 in Format A.

These octets and the octets that carry the

performance bits of the preceding three one-second intervals form the periodic performance report.

The periodic performance report is made up of 14 bytes of data. Bytes 1 to 4, 13, and 14 are the message

header and bytes 5 to 12 contain data regarding the four most-recent one-second intervals. The periodic

performance report message uses the SAPI/TEI value of 0x14.

3.8.3

Transmission-Error Event

Occurrences of transmission-error events indicate the quality of transmission. The occurrences that shall be

detected and reported are:

• CRC Error Event: A CRC-6 error event is the occurrence of a received CRC code that is not identical to the

corresponding locally calculated code.

• Severely Errored Framing Event: A severely-errored-framing event is the occurrence of two or more framing-

bit-pattern errors within a 3-ms period. Contiguous 3-ms intervals shall be examined. The 3-ms period may

coincide with the ESF. The severely-errored-framing event, while similar in form to criteria for declaring a

FIGURE 33. LAPD FRAME STRUCTURE

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