The Sockets Networking API: UNIX® Network Programming Volume 1, Third Edition

Chapter 24. Out-of-Band Data

Introduction

Many transport layers have the concept of out-of-band data, which is sometimes called expedited data. The idea is that something important occurs at one end of a connection and that end wants to tell its peer quickly. By “quickly” we mean that this notification should be sent before any “normal” (sometimes called “in-band”) data that is already queued to be sent, and should be sent regardless of any flow control or blocking issues. That is, out-of-band data is considered higher priority than normal data. Instead of using two connections between the client and server, out-of-band data is mapped onto the existing connection.

Unfortunately, once we get beyond the general concepts and down to the real world, ...