Final answer:
The protocol that requires senders to maintain a timer for each unacknowledged packet is the Transmission Control Protocol (TCP), which is a fundamental protocol for reliable and ordered data transmission in the Internet protocol suite.
Step-by-step explanation:
The protocol that requires senders to maintain a timer for each unacknowledged packet is the Transmission Control Protocol (TCP). TCP is a core protocol of the Internet protocol suite and enables reliable, ordered, and error-checked delivery of a stream of data between applications running on hosts communicating over an IP network. The role of the timer in TCP is critical for ensuring data integrity and controlling the flow of information.When a packet is sent, TCP starts a timer expecting an acknowledgment (ACK) of receipt from the receiver within a certain time frame. If the ACK is not received before the timer expires, TCP assumes the packet has been lost and retransmits it. This is part of TCP's built-in mechanisms for handling lost or corrupted packets, network congestion, and other issues that can affect data transmission