Alcatel-Lucent 1643 AMS User's Operation Manual page 106

Management communication setup
LAPD protocol
The LAPD protocol, which controls communication between the network elements,
operates in either of the following modes:
• Network Side
The LAPD is assigned as Network. This mode complies with the standards and
interoperates successfully with other LAPDs operating in user_side mode.
• User Side
The LAPD is assigned as User. This mode complies with the standards and
interoperates successfully with other LAPDs operating in network_side mode.
Please note that the DCCs work according to the master/slave principle, i.e. the LAPD
modes of two interconnected SDH ports must be set differently. A corresponding
"User-Network Side Failure" alarm will be generated if the LAPD mode is the same at
both ends of a DCC.
AITS and UITS supported
1643 AM or 1643 AMS network elements support the Acknowledged Information
Transfer Service (AITS) and the Unacknowldeged Information Transfer Service (UITS)
as the basis for the LAPD or LinkID protocol with the UITS mode being the default
mode of operation. AITS should only be used if required by other NE types. UITS is
furthermore used for link protocol at the same time when AITS is chosen.
AITS and UITS functional principles
In the LAPD protocol, all PDUs are sent with a checksum to verify that the data has
not been corrupted during the transmission over the DCC link. If a PDU is received
with a bad checksum, it is not acknowledged and will be resent:
• In the Unacknowldeged Information Transfer Service (UITS) (default), corrupted
PDUs are ignored and no further actions taken. Upper layers of the OSI stack are
responsible for recovery actions.
• In the Acknowldeged Information Transfer Service (AITS), PDUs are numbered and
transmitted sequentially, and acknowledgment PDUs are sent back from the
receiver to the sender. If a PDU is lost, that is, if the sender gets no
acknowledgment, the PDU is retransmitted.
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4-16 Alcatel-Lucent - Proprietary
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Data communication channels
365-312-807R7.2
Issue 4, May 2007