Information Technology Reference
In-Depth Information
store, and you pay for your purchase with a credit card, the cash regis-
ter's software checks a credit card verification server to make sure your
card is valid before charging your purchase. It then sends the informa-
tion to the store's internal inventory management system via the local
network. The local server then sends an updated inventory report to the
company's web server, so that someone ordering from the store's website
will know that the item is no longer in stock. When you call your mother
on your cell phone on the way home to tell her about your purchase,
your call goes through the wireless network for your cell phone provider.
Let's start out this chapter by looking at some of the large-scale networks
that make up our connected world.
Public Telephone and Data Networks
The first worldwide network ever created was the telephone network,
predating computers by many decades. This network is an example
of a
circuit-switched network
. It works by creating a point-to-point
circuit between the two locations. The telephone network creates a
pathway between the two points, and that pathway remains open for
the duration of the phone call. Networks can be public or private. The
public telephone system—the whole of the world's circuit-switched
telephone networks—is known as the
public-switched telephone
network (PSTN)
.
circuit-switched network
A network that
creates a point-to-point connection between
locations that remains open for the duration of the
communication.
public switched telephone network
(PSTN)
The worldwide network of circuit-switched
telephone lines.
In contrast, computer networks are
packet-switched networks
. A com-
munication channel does not remain open between two points for an
entire conversation; instead, the data is broken up at the sending end
into small packets, each with an electronic envelope around it that states
the source and the destination, and sent individually to the receiver.
Depending on the network traffic, each packet may take a different route
to the destination, but when they arrive they are unpacked and reassem-
bled into the original message.
packet-switched network
A network that
transfers data by breaking it up into separately
transferred packets.
The Internet
The
Internet
is the world's largest network. It is not owned or main-
tained by any one company; instead, it is a cooperative effort among
many companies and governments, with multiple standards organizations
managing the rules for its operation. The Internet is a packet-switched
network with a worldwide addressing system. The Internet uses vari-
ous
protocols
(rules) that all participating computers have standardized
on, so that services like the web, email, and instant messaging work the
same everywhere. Most companies and individuals don't connect directly
to the Internet; instead, they connect to an
Internet service provider
(ISP)
, which in turn connects to the Internet. For example, if you have
cable Internet at home, your ISP is your cable provider.
Internet
A global packet-switched network
created cooperatively by multiple companies,
governments, and standards organizations.
protocol
A rule or custom that governs how
something is done. In a computer context, it refers
to a standard for transferring data.
Internet service provider (ISP)
A company
that maintains a direct connection to the Internet
and leases access to it to individuals and
companies.
The Internet is based on a
protocol stack
(a set of protocols) called
Transmission Control Protocol/Internet Protocol (TCP/IP)
. TCP/
IP provides a common set of standards by which data can be sent and
received. It is used not only on the Internet, but in most private net-
works today as well. One of the key features of TCP/IP is IP addressing,
which is a means of uniquely identifying each connected computer on
the network by a numeric value.
protocol stack
A related group of protocols—for
example, TCP/IP.
TCP/IP
The protocol suite (set of rules) that
defines how data will move on the Internet and on
most other modern networks.
