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Technology Infrastructure: The Internet and the World Wide Web

The Internet of Things
The most common perception of the Internet is that it connects computers to one another
and, by doing so, connects the users of those computers to each other. In recent years, 65
devices other than computers have been connected to the Internet, such as mobile
phones and tablet devices. Once again, the connection of these devices to the Internet
serves to connect the users of those devices to each other. However, the connection of
devices to the Internet that are not used by persons is increasing rapidly. These devices—
such as switches, optical scanners, sensors that detect changes in temperature, light,
moisture, or the existence of vibration or movement—can be connected to the Internet
and used by computers to manage automatically environmental conditions (such as
heating and cooling or lighting levels) or security procedures. These interconnected
devices can be located in houses, offices, factories, autos, appliances, and so on.
Computers can also be connected to each other using the Internet to conduct
business transactions without human intervention. For example, a computer that
monitors inventory levels using sensors connected to it over the Internet can use its
Internet connection to place inventory orders with a vendor’s computer automatically.
The subset of the Internet that includes these computers and sensors connected to each
other for communication and automatic transaction processing is often called the Internet
of Things. Industry analysts estimate that the number of devices, sensors, switches, and
computers that are interconnected in the Internet of Things is 9 billion (more than the
number of people on Earth) and will reach 35 billion by 2020.
From its humble beginnings in 1969, the Internet has grown to become one of the
most significant technological and social accomplishments of the last millennium. Millions
of people, from elementary school students to research scientists, now use this complex,
interconnected network of computers located in almost every country of the world.
Billions of dollars change hands each year over the Internet in exchange for all kinds of
products and services. And all of this activity occurs with no central coordination point or
control, which is especially ironic given that the Internet began as a way for the military
to maintain control of weapons systems while under attack.
The Internet is a set of interconnected networks. Thus, to understand the
technologies used to build the Internet, you must first learn about the structure of its
component networks.

PACKET-SWITCHED NETWORKS
A network of computers that are located close together—for example, in the same
building—is called a local area network (LAN). Networks of computers that are connected
over greater distances are called wide area networks (WANs).
The early models (dating back to the 1950s) for WANs were the circuits of the local
and long-distance telephone companies of the time because the first early WANs used
leased telephone company lines for their connections. A telephone call establishes a single
connection path between the caller and receiver. Once that connection is established,
data travels along that single path. Telephone company equipment (originally mechanical,
now electronic) selects specific telephone lines to connect to one another by closing

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