Chapter 25. TCP Timers

Introduction

We start our detailed description of the TCP source code by looking at the various TCP timers. We encounter these timers throughout most of the TCP functions.

TCP maintains seven timers for each connection. They are briefly described here, in the approximate order of their occurrence during the lifetime of a connection.

  1. A connection-establishment timer starts when a SYN is sent to establish a new connection. If a response is not received within 75 seconds, the connection establishment is aborted.

  2. A retransmission timer is set when TCP sends data. If the data is not acknowledged by the other end when this timer expires, TCP retransmits the data. The value of this timer (i.e., the amount of time TCP waits for an acknowledgment) ...

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