Introduction To Computer Networks

Introduction to
COMPUTER NETWORKS
15-1
Networking
Computer network A collection of

computing devices that are connected in
various ways in order to communicate and
share resources.
Usually, the connections between
computers in a network are made using
physical wires or cables.
However, some connections are wireless,
using radio waves or infrared signals.
15-2
Networking
The generic term node or host refers to

any device on a network.
Data transfer rate The speed with which
data is moved from one place on a
network to another.
Data transfer rate is a key issue in
computer networks.
15-3
Networking
Computer networks have opened up an

entire frontier in the world of computing
called the client/server model.
Figure 15.1 Client/Server interaction

15-4
Networking
File server A computer that stores and

manages files for multiple users on a
network.
Web server A computer dedicated to
responding to requests (from the browser
client) for web pages.
15-5
Types of Networks
Local-area network (LAN) A network

that connects a relatively small number of
machines in a relatively close
geographical area.
15-6
Types of Networks
Various configurations, called topologies, have

been used to administer LAN's.
Ring topology A configuration that connects all
nodes in a closed loop on which messages travel in
one direction.
Star topology A configuration that centers around
one node to which all others are connected and
through which all messages are sent.
Bus topology All nodes are connected to a single
communication line that carries messages in both
directions.
15-7
Types of Networks
Figure 15.2 Various network topologies
A bus technology called Ethernet has become the

industry standard for local-area networks.
15-8
Types of Networks
Wide-area network (WAN) A network that connects two or

more local-area networks over a potentially large geographic
distance.
Often one particular node on a LAN is set up to serve as

a gateway to handle all communication going between
that LAN and other networks
Communication between networks is called inter-networking.
The Internet, as we know it today, is essentially the

ultimate wide-area network, spanning the entire globe.
15-9
Types of Networks
Metropolitan-area network (MAN) The

communication infrastructures that have
been developed in and around large cities.
15-10
So, who owns the Internet?
Well, nobody does. No single person or

company owns the Internet or even
controls it entirely. As a wide-area
network, it is made up of many smaller
networks. These smaller networks are
often owned and managed by a person or
organization. The Internet, then, is really
defined by how connections can be made
between these networks.
15-11
Types of Networks
Figure 15.1 Local-area networks connected across a distance to

create a wide-area network
15-12
Internet Connections
Internet backbone A set of high-speed networks that

carry Internet traffic.
These networks are provided by companies such as
AT&T, GTE, and IBM.
Internet service provider (ISP) A company that
provides other companies or individuals with access to
the Internet.
15-13
There are various technologies available that you can

use to connect a home computer to the Internet.
A phone modem converts computer data into an analog
audio signal for transfer over a telephone line, and then a
modem at the destination converts it back again into data.
A digital subscriber line (DSL) uses regular copper phone
lines to transfer digital data to and from the phone companys
central office.
A cable modem uses the same line that your cable TV
signals come in on to transfer the data back and forth.
15-14
Broadband A connection in which transfer

speeds are faster than 128 bits per second.
DSL connections and cable modems are broadband
connections.
The speed for downloads (getting data from the
Internet to your home computer) may not be the same
as uploads (sending data from your home computer
to the Internet).
15-15
Packet Switching
To improve the efficiency of transferring information over

a shared communication line, messages are divided into
fixed-sized, numbered packets.
Network devices called routers are used to direct
packets between networks.
Figure 15.4
Messages
sent by
packet
switching
15-16
Open Systems
Proprietary system A system that uses technologies kept

private by a particular commercial vendor.
One system couldnt communicate with another,

leading to the need for
Interoperability The ability of software and hardware on
multiple machines and from multiple commercial vendors to
communicate.
Open systems Systems based on a common model of
network architecture and a suite of protocols used in its
implementation.
15-17
Open Systems
The International
Organization for
Standardization(ISO)
established the Open
Systems
Interconnection (OSI)
Reference Model.
Each layer deals with a
particular aspect of
Figure 15.5 The layers of the OSI Reference Model network
communication.
15-18
Network Protocols
Network protocols are layered such that each one relies on

the protocols that underlie it.
Sometimes referred to as a protocol stack.
Figure 15.6 Layering of key network protocols
15-19
TCP/IP
TCP stands for Transmission Control Protocol

TCP software breaks messages into packets,
hands them off to the IP software for delivery,
and then orders and reassembles the packets
at their destination.
IP stands for Internet Protocol
IP software deals with the routing of packets
through the maze of interconnected networks
to their final destination.
15-20
TCP/IP (cont.)
UDP stands for User Datagram Protocol

It is an alternative to TCP
The main difference is that TCP is highly
reliable, at the cost of decreased
performance, while UDP is less reliable, but
generally faster.
15-21
High-Level Protocols
Other protocols build on the foundation

established by the TCP/IP protocol suite.
Simple Mail Transfer Protocol (SMTP)
File Transfer Protocol (FTP)
Telnet
Hyper Text Transfer Protocol (http)
15-22
MIME Types
Related to the idea of network protocols and

standardization is the concept of a files MIME type.
MIME stands for Multipurpose Internet Mail

Extension.
Based on a documents MIME type, an
application program can decide how to deal
with the data it is given.
15-23
MIME Types
Figure 15.7
Some
protocols and
the ports they
use
15-24
Firewalls
Firewall A machine and its software that

serve as a special gateway to a network,
protecting it from inappropriate access.
Filters the network traffic that comes in,
checking the validity of the messages as
much as possible and perhaps denying some
messages altogether.
Enforces an organizations access control
policy.
15-25
Firewalls
Figure 15.8 A firewall protecting a LAN

15-26
Network Addresses
Hostname A unique identification that

specifies a particular computer on the
Internet.
For example
matisse.csc.villanova.edu
condor.develocorp.com
15-27
Network Addresses
Network software translates a hostname

into its corresponding IP address.
For example
205.39.145.18
15-28
Network Addresses
An IP address can be split into

network address, which specifies a specific network
host number, which specifies a particular machine in
that network
Figure 15.9
An IP address is
stored in four
bytes
15-29
Domain Name System
A hostname consists of the computer name

followed by the domain name
csc.villanova.edu is the domain name
A domain name is separated into two or more
sections that specify the organization, and possibly a
subset of an organization, of which the computer is a
part.
Two organizations can have a computer named the
same thing because the domain name makes it clear
which one is being referred to.
15-30
Domain Name System
The very last section of the domain is called its top-level

domain (TLD) name.
Figure 15.10 Top-level domains, including some relatively new ones

15-31
Domain Name System
Organizations based in countries other than the United States

use a top-level domain that corresponds to their two-letter
country codes.
Figure 15.11
Some of the top-level domain
names based on country codes
15-32
Domain Name System
The domain name system (DNS) is chiefly used to

translate hostnames into numeric IP addresses,
DNS is an example of a distributed database
If that server can resolve the hostname, it
does so
If not, that server asks another domain name
server
15-33
15-34

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Introduction To Computer Networks

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Introduction to

Computer network A collection of

The generic term node or host refers to

Computer networks have opened up an

Figure 15.1 Client/Server interaction

File server A computer that stores and

Local-area network (LAN) A network

Various configurations, called topologies, have

Figure 15.2 Various network topologies

A bus technology called Ethernet has become the

Wide-area network (WAN) A network that connects two or

Often one particular node on a LAN is set up to serve as

The Internet, as we know it today, is essentially the

Metropolitan-area network (MAN) The

Well, nobody does. No single person or

Figure 15.1 Local-area networks connected across a distance to

Internet backbone A set of high-speed networks that

There are various technologies available that you can

Broadband A connection in which transfer

To improve the efficiency of transferring information over

Proprietary system A system that uses technologies kept

One system couldnt communicate with another,

Network protocols are layered such that each one relies on

Sometimes referred to as a protocol stack.

Figure 15.6 Layering of key network protocols

TCP stands for Transmission Control Protocol

UDP stands for User Datagram Protocol

Other protocols build on the foundation

Related to the idea of network protocols and

MIME stands for Multipurpose Internet Mail

Firewall A machine and its software that

Figure 15.8 A firewall protecting a LAN

Hostname A unique identification that

Network software translates a hostname

An IP address can be split into

A hostname consists of the computer name

The very last section of the domain is called its top-level

Figure 15.10 Top-level domains, including some relatively new ones

Organizations based in countries other than the United States

The domain name system (DNS) is chiefly used to

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