xr
PRELIMINARY
XRT86VL38
REV. P1.0.6
OCTAL T1/E1/J1 FRAMER/LIU COMBO
326
5.8.2
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.
5.8.3
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
F
IGURE
39. LAPD F
RAME
S
TRUCTURE