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Chapter 7 Telecommunications, the Internet, and Wireless Technology 281

The network operating system (NOS) routes and manages communi-
cations on the network and coordinates network resources. It can reside on
every computer in the network, or it can reside primarily on a dedicated
server computer for all the applications on the network. A server computer is
a computer on a network that performs important network functions for client
computers, such as serving up Web pages, storing data, and storing the network
operating system (and hence controlling the network). Server software such as
Microsoft Windows Server, Linux, and Novell Open Enterprise Server are the
most widely used network operating systems.
Most networks also contain a switch or a hub acting as a connection point
between the computers. Hubs are very simple devices that connect network
components, sending a packet of data to all other connected devices. A switch
has more intelligence than a hub and can filter and forward data to a specified
destination on the network.
What if you want to communicate with another network, such as the
Internet? You would need a router. A router is a communications processor
used to route packets of data through different networks, ensuring that the data
sent gets to the correct address.
Network switches and routers have proprietary software built into their
hardware for directing the movement of data on the network. This can create
network bottlenecks and makes the process of configuring a network more
complicated and time-consuming. Software-defined networking (SDN) is a
new networking approach in which many of these control functions are man-
aged by one central program, which can run on inexpensive commodity servers
that are separate from the network devices themselves. This is especially help-
ful in a cloud computing environment with many different pieces of hardware
because it allows a network administrator to manage traffic loads in a flexible and
more efficient manner.
Networks in Large Companies
The network we’ve just described might be suitable for a small business. But what
about large companies with many different locations and thousands of employ-
ees? As a firm grows, and collects hundreds of small local area networks, these
networks can be tied together into a corporate-wide networking infrastructure.
The network infrastructure for a large corporation consists of a large number
of these small local area networks linked to other local area networks and to
firmwide corporate networks. A number of powerful servers support a corporate
Web site, a corporate intranet, and perhaps an extranet. Some of these servers
link to other large computers supporting back-end systems.
Figure 7.2 provides an illustration of these more complex, larger scale
corporate-wide networks. Here you can see that the corporate network infra-
structure supports a mobile sales force using cell phones and smartphones,
mobile employees linking to the company Web site, internal company networks
using mobile wireless local area networks (Wi-Fi networks), and a videoconfer-
encing system to support managers across the world. In addition to these com-
puter networks, the firm’s infrastructure usually includes a separate telephone
network that handles most voice data. Many firms are dispensing with their
traditional telephone networks and using Internet telephones that run on their
existing data networks (described later).
As you can see from this figure, a large corporate network infrastructure uses
a wide variety of technologies—everything from ordinary telephone service and
corporate data networks to Internet service, wireless Internet, and cell phones.
One of the major problems facing corporations today is how to integrate all

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