When a connectionless protocol is in use at a lower layer of the OSI model, how is missing data detected and retransmitted if necessary?

Question:
When a connectionless protocol is in use at a lower layer of the OSI model, how is missing data detected and retransmitted if necessary?

• Connectionless acknowledgements are used to request retransmission.
• Upper-layer connection-oriented protocols keep track of the data received and can request retransmission from the upper-level protocols on the sending host.
• Network layer IP protocols manage the communication sessions if connection-oriented transport services are not available.
• The best-effort delivery process guarantees that all packets that are sent are received.

Explanation: When connectionless protocols are in use at a lower layer of the OSI model, upper-level protocols may need to work together on the sending and receiving hosts to account for and retransmit lost data. In some cases, this is not necessary, because for some applications a certain amount of data loss is tolerable.

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