Retransmission timeout

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

A retransmission timeout is the period a TCP sender waits for an acknowledgment before retransmitting an unacknowledged segment.

A retransmission timeout is the period a TCP sender waits for an acknowledgment before retransmitting an unacknowledged segment. This timer supports reliable communication: when an acknowledgment does not arrive in time, TCP sends the segment again. section 22.2.1 section 22.3

Lost TCP segment

PC1 sends a segment with sequence number 26, but the segment does not reach SRV1. Because PC1 receives no acknowledgment before the timeout expires, it retransmits the segment; SRV1 then receives and acknowledges it. A corrupted segment can produce the same result when TCP’s checksum causes the receiver to discard it without acknowledging it. section 22.2.1

Figure 22.9 TCP retransmission. PC1’s first segment with sequence number 26 does not reach SRV1. Because PC1 doesn’t receive an acknowledgment for the segment, it retransmits the segment, which is then received and acknowledged by SRV1.

Trace the lost-segment scenario and connect the missing acknowledgment to TCP retransmission. section 22.2.1

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes

Explains the timeout trigger and retransmission sequence, but does not cover timeout calculation or configuration commands.

Examples

Uses PC1 and SRV1, sequence number 26, a lost segment, and checksum-detected corruption.

What it assumes

Assumes TCP segments and acknowledgments while introducing how missing acknowledgments trigger reliable delivery.

What you can do after

Evaluate TCP reliability by tracing missing acknowledgments, timeout expiry, and segment retransmission.

How it connects

Connects TCP acknowledgment, sequence numbers, checksums, and reliable communication.

liveBookmanning.com

Read Acing the CCNA Exam: Volume 1 Fundamentals and Protocols on liveBook Get the book at manning.com

Related concepts

• timeruses · A timer is a hardware or software mechanism that tracks time and triggers an event or action after a specified duration or at scheduled intervals.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.