XRT84L38 Datasheet, PDF (415/451 Pages) Exar Corporation – OCTAL T1/E1/J1 FRAMER

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XRT84L38
OCTAL T1/E1/J1 FRAMER
REV. 1.0.0
13.1.4.1 Discussion of MOS
Message-Oriented signals (MOS) sent by the transmit LAPD Controller are messages conforming to ITU Rec-
ommendation Q.921 LAPD protocol as defined below.
Two types of Message-Oriented signals are defined. One is a periodic performance report generated by the
source or sink T1/E1 terminals as defined by ANSI T1.403. The other is a path or test signal identification mes-
sage that may be optionally generated by a terminal or intermediate equipment on a T1/E1 circuit.
Message-oriented signals shall use the frame structure, field definitions and elements of procedure of the
LAPD protocol defined in ITU recommendation Q.921 except the address field. Performance information is car-
ried by Message-Oriented signal using LAPD protocol. The message structures of the periodic performance
report and path or test signal identification message are shown in Figure 128 in format A and format B respec-
tively.
FIGURE 128. LAPD FRAME STRUCTURE
Flag
Address
(high order)
Address
(low order)
8 7 6 5 43 2
Flag
0111111
1 Octet
01
SAPI
C/R
EA
0
2
TEI
EA
1
3
Control
4
Information
5
One-second counts
.
.
12
FCS
(first octet)
FCS
(second octet)
Flag
Flag
0111111
13
14
0
Format A
Flag
Address
(high order)
Address
(low order)
8 7 6 5 43 2
Flag
0111111
1 Octet
01
SAPI
C/R
EA
0
2
TEI
EA
1
3
Control
4
Information
5
76 octets
.
.
80
FCS
(first octet)
FCS
(second octet)
Flag
Flag
0111111
81
82
0
Format B
13.1.4.1.1 Periodic Performance Report
The ANSI T1.403 standard requires that the status of the transmission quality be reported every one-second
interval. 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 with respect to the occurrence of error events is arbi-
trary; that is, the one-second timing 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-sec-
ond 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 per-
formance report message uses the SAPI/TEI value of 14.
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