Computer Networks and the Internet 1

Today's Internet is arguably the largest engineered system ever created by mankind,
with hundred of millions of connected computers, communication links, and
switches; hundreds of millions of users who connect intermittently via cell phones
and PDAs; and devices such as sensors, webcams, game consoles, picture frames,
and even washing machines being connected to the Internet. Given that the Internet
is so large and has so many di verse components and uses, is there any hope of
understanding how it (and more generally computer networks) work? Are there
guiding principles and structure that can provide a foundation for understanding
such an amazingly large and complex system') And if so, is it possible that it actually
could be both interesting and fun to learn about computer networks? Fortunately,
the answers to all of these questions is a resounding YES! Indeed, it's our
aim in this book to provide you with a modern introduction to the dynamic field of
computer networking. giving you the principles and practical insights you'll need to
understand not only today 's networks, but tomorrow's as well.
This first chapter presents a broad overview of computer networking and the
Internet. Our goal here is to paint a broad picture and set the context for the rest of
this book, 10 see the forest through the trees. We'll cover a lot of ground in this introductory
chapter and discuss a lot of the pieces of a computer network, without losing
sight of the big picture.

We ' ll structure our overview of computer networks in this chapter as follows.
After jntroducing some basic terminology and concepts, we'll first examine the
basic hardware and software components that make up a network. We'll begin at the
network's edge and look at the end systems and network applications running in the
network, We'il then explore the core of a computer network, examining the links
and the switches that transport data, as well as the access networks and physical
media that connect end systems to the network core. We'll learn that the Internet is a
network of networks, and we' ll learn how these networks connect with each other.
After havi.ng completed this overview of the edge and core of a computer network,
we' ll take the broader and more abstract view in the second half of this chapter.
We'll examine delay, loss, and throughput in a computer network and provide
simple quantitative mode ls for end-to-end throughput and delay: models that take
into account transmission, propagation, and queuing delays. We'll then introduce
some of the key architectural principles in computer networking, namely, protocol
layering and service models. We' ll also learn that computer networks are vulnerable
to many different types of attacks; we'll survey some of these attacks and consider
how computer networks can be made more secure. Finally, we'll close this chapter
with a brief history of computer networking.