XRT86L30
SINGLE T1/E1/J1 FRAMER/LIU COMBO
REV. 1.0.1
6.7
Transmit MOS (Message Oriented Signaling) Processor
The Transmit LAPD controller implements the Message-Oriented protocol based on ITU Recommendation
Q.921 Link Access Procedures on the D-channel. It provides the following functions.
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Zero stuffing
T1/E1 transmitter interface
Transmit message buffer access
Frame check sequence generation
IDLE flag insertion
ABORT sequence generation
Two 96-byte buffers in shared memory are allocated for each LAPD to reduce the frequency of microprocessor
interrupts and alleviate the response time requirement for a microprocessor to handle each interrupt. There
are no restrictions on the length of the message. However the 96-byte buffer is deep enough to hold one entire
LAPD path or test signal identification message.
6.7.1
Discussion of MOS
Message-Oriented signals sent by the transmit LAPD Controller are messages conforming to ITU
Recommendation Q.921 LAPD protocol. There are two types of Message-Oriented signals. 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 message that may be optionally generated by a terminal or intermediate
equipment on a T1/E1 circuit. The message structures of the performance report and path or test signal
identification message are shown in Figure 35 for format A and format B respectively.
FIGURE 35. LAPD FRAME STRUCTURE
6.7.2
Periodic Performance Report
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