TCP/IP Illustrated

Chapter 22. Protocol Control Blocks

22.1. Introduction

Protocol control blocks (PCBs) are used at the protocol layer to hold the various pieces of information required for each UDP or TCP socket. The Internet protocols maintain Internet protocol control blocks and TCP control blocks. Since UDP is connectionless, everything it needs for an end point is found in the Internet PCB; there are no UDP control blocks.

The Internet PCB contains the information common to all UDP and TCP end points: foreign and local IP addresses, foreign and local port numbers, IP header prototype, IP options to use for this end point, and a pointer to the routing table entry for the destination of this end point. The TCP control block contains ...