You are capturing packets with a network sniffer and notice a number of packets that are flagged by the sniffer and described as TCP retries. Which layer of the OSI model should you investigate?

Transport Layer

Explanation:

Transport layer is responsible for correcting data transmission errors which is done by requesting retries also called re-transmission of packets in case of data loss or corrupted data. Transport layer ensures end to end delivery of data making sure that the data is received correctly and in same order in which it was sent. Transmission Control Protocol (TCP) is a protocol in this layer that continues to transmit data packets securely from sender to receiver, identifying packet losses. Transport layer works on packet loss issues and corrects data transmission errors. It has flow control and error control services manage data transmission rate and ensures data is received without error. So in case of transmission errors and re-transmission requests transport layer should be investigated.