liveBook · Manning

Retransmission

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

TCP retransmission is the sending of a segment again after its acknowledgment is not received within the retransmission timeout or its integrity check fails.

TCP retransmission sends a segment again when its acknowledgment is not received within the retransmission timeout or its integrity check fails. It helps TCP provide reliable, sequenced communication: the receiver acknowledges each segment by identifying the next sequence number it expects. section 22.2.1

Lost segment

PC1 sends a segment with sequence number 26, but the segment does not reach SRV1. Because PC1 receives no acknowledgment, it retransmits the segment; SRV1 then receives and acknowledges it.

Keep these protocol behaviors distinct:

  • TCP uses acknowledgments and retransmissions to recover from lost segments. section 22.2.1
  • UDP provides error detection through a checksum but does not retransmit messages with errors or messages that are lost. section 22.2.2

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

How deep it goes
Defines retransmission and works through one lost-segment example without detailing timeout calculation or retransmission algorithms.
Examples
Uses PC1 and SRV1 to show sequence number 26 being retransmitted after the original segment is lost.
What you can do after
Evaluate how TCP recovers from lost segments and distinguish its reliability mechanisms from UDP behavior.
How it connects
Connects retransmission with TCP, acknowledgments, sequence numbers, reliability, checksums, and UDP.
Cover of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols
liveBookmanning.com
Read Acing the CCNA Exam: Volume 1 Fundamentals and Protocols on liveBook Get the book at manning.com

Related concepts

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.