It's hard to imagine that anyone reading this book doesn't have some intuitive idea of what a network actually is. As I write this introduction, I'm surrounded by no fewer than six distinct, network-connected devices within arm's reach. Even before I began a career in software engineering, I could have given a reasonably accurate description of what constitutes a network. However, no amount of intuition about what networks are or what might run on them, nor the use of software running on distributed systems, can account for the impact of a distributed architecture on your code. It's that impact on your software design and implementation decisions that we'll cover in this chapter.

We'll try to nail down a concrete definition of a network, and we'll consider the new problems you'll need to solve when writing software...