XRT86L30
REV. 1.0.1
SINGLE T1/E1/J1 FRAMER/LIU COMBO
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.
6.7.3
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
terminal has lost framing, is only designed as a performance indicator; existing terminal out-of-frame criteria
will continue to serve as the basis for terminal alarms.
•
•
Frame-Synchronization-Bit Error Event: A frame-synchronization-bit-error event is the occurrence of a
received framing-bit-pattern not meeting the severely-errored-framing event criteria.
Line-Code Violation event: A line-code violation event is a bipolar violation of the incoming data. A line-code
violation event for an B8ZS-coded signal is the occurrence of a received excessive zeros (EXZ) or a bipolar
violation that is not part of a zero-substitution code.
•
Controlled Slip Event: A controlled-slip event is a replication, or deletion, of a T1 frame by the receiving
terminal. A controlled slip may occur when there is a difference between the timing of a synchronous
receiving terminal and the received signal.
6.7.4
Path and Test Signal Identification Message
The path identification message is used to identify the path between the source terminal and the sink terminal.
The test signal identification message is used by test signal generating equipment. Both identification
messages are made up of 82 bytes of data. Byte 1 to 4, 81 and 82 are the message header and bytes 5 to 80
contain six data elements. These messages use the SAPI/TEI value of 0x15 to differentiate themselves from
the performance report message.
6.7.5
Frame Structure
The message structure of message-oriented signal is shown in Figure 35. Two format types are shown in the
figure: format A for frames which are sending performance report message and format B for frames which
containing a path or test signal identification message. The following abbreviations are used:
•
•
•
•
•
SAPI: Service Access Point Identifier
C/R: Command or Response
EA: Extended Address
TEI: Terminal Endpoint Identifier
FCS: Frame Check Sequence
6.7.6
Flag Sequence
All frames shall start and end with the flag sequence consisting of one 0 bit followed by six contiguous 1 bits
and one 0 bit. The flag preceding the address field is defined as the opening flag. The flag following the Frame
Check Sequence (FCS) field is defined as the closing flag. The closing flag may also serve as the opening flag
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