XRT86VL32IB datasheet(33/153 Pages) EXAR

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XRT86VL3X

REV. 1.2.2

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

3.8

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.

• 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.

3.8.1

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 33 for format A and format B respectively.

XRT86VL32IB Datasheet(PDF) 33 Page - Exar Corporation