The Network Edge

The Network Edge

In the previous section we presented a high-level overview of the Internet and networking

protocols. We are now going to delve a bit more deeply into the components

of a computer network (and the Internet, in particular). We begin in this

section at the edge of a network and look at the components with which we are most

familiar—namely, the computers, smartphones and other devices that we use on a

daily basis. In the next section we’ll move from the network edge to the network

core and examine switching and routing in computer networks.

Recall from the previous section that in computer networking jargon, the computers

and other devices connected to the Internet are often referred to as end systems.

They are referred to as end systems because they sit at the edge of the Internet,

as shown in Figure 1.3. The Internet’s end systems include desktop computers (e.g.,

desktop PCs, Macs, and Linux boxes), servers (e.g., Web and e-mail servers), and

mobile computers (e.g., laptops, smartphones, and tablets). Furthermore, an increasing

number of non-traditional devices are being attached to the Internet as end systems

(see sidebar).

End systems are also referred to as hosts because they host (that is, run) application

programs such as a Web browser program, a Web server program, an e-mail

client program, or an e-mail server program. Throughout this book we will use the

terms hosts and end systems interchangeably; that is, host = end system. Hosts are

sometimes further divided into two categories: clients and servers. Informally,

clients tend to be desktop and mobile PCs, smartphones, and so on, whereas servers

tend to be more powerful machines that store and distribute Web pages, stream

video, relay e-mail, and so on. Today, most of the servers from which we receive

search results, e-mail, Web pages, and videos reside in large data centers. For

example, Google has 30–50 data centers, with many having more than one hundred

thousand servers.