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
unacknowledged 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
acknowledged information transfer service (AITS), PDUs are numbered and
transmitted sequentially, and acknowledgement PDUs are sent back from the
receiver to the sender. If a PDU is lost, that is, if the sender gets no
acknowledgement, the PDU is retransmitted.
Functional principle of the AITS
DCC over 1+1 MSP protected interfaces
To support DCC communication over 1+1 MSP protected STM-
n
links, two modes of
operation are defined, which can be selected independently for RS-DCC and MS-DCC
1.
MSP DCC Independent Mode
In this mode the DCC channels over the working and protection STM-
n
interface
operate independently from the MSP protocol and can individually be
enabled/disabled. DCC protection is performed at the IS-IS protocol level.
2.
MSP DCC Slave Mode
In this case the DCC information in the transmit direction is bridged over both the
working and the protection part of the MSP connection. At the receive end the
DCC is retrieved from the service (= active) part.
1
Node A
Node B
2
3
Ack. 1
Ack. 2
no Ack. 3 !
3
retransmission of
Ack. 3
PDU 3 corrupted
Management communication setup concepts
Data communication channels (DCC)
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365-312-875R5.2
Issue 1, March 2007
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