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Chapter 1
Introduction
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Introduction
 A computer network is two or more computers connected together so
they can communicate with one another.
Two computers are interconnected if they can exchange information
among them.
These interconnected computers are called Computer networks
Today, single main frame computer is not serving all the computation
needs, but a large number of interconnected computers will do.
Computers networks vary in their size, communication media and speed
of data transmission.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Uses of Computer Networks
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Business Applications
Home Applications
Mobile Users
Social Issues
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Benefits and uses of computer networks (1/3)
 Business applications:
companies that have large number of computers can
benefit from computer networks as follows:
•Hardware sharing: like printers, hard drives and scanners,
•Send files from one computer to another quite easily
•Connectivity and Communication: Networks connect computers
and the users within a building or work group can be connected
into local area networks (LANs); users in distant locations can be
interconnected into larger wide area networks (WANs).
•Run programs that installed on central computers (servers) but
are not installed on any other user's computer.
•Internal e-mail services
•E-commerce.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Business Applications of Networks
A network with two clients and one server.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Business Applications of Networks (2)
The client-server model involves requests and replies.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Benefits and uses of computer networks (contd. 2/3)
•Data Security and Management: computer networks allow
the administrators to manage the company's critical data.
Instead of having this data spread over a large number of
small computers data can be centralized on shared servers.
This makes it easy for everyone to find the data, backup data
on regular basis, and allows for the implementation of security
measures to control who can read or change critical
information.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Home Network Applications
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Access to remote information
Person-to-person communication
Interactive entertainment
Electronic commerce
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Benefits and uses of computer networks (contd.3/3)
Home applications:
Sharing resources like printers, scanners
share a single Internet connection on all the home
PCs.
Interactive entertainment : e.g. Video on demand on
the internet
Peer to peer communication to share music
Connecting home appliances together
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Home Network Applications (2)
In peer-to-peer system there are no fixed clients and servers.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Home Network Applications (3)
Some forms of e-commerce.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Mobile users:
•
The growth of notebook computers and PDAs enable people to stay
connected to their offices or the Internet when they are away from their
home even though there is no wire connection exists
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Mobile Network Users
Combinations of wireless networks and mobile computing.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Network Hardware
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Local Area Networks
Metropolitan Area Networks
Wide Area Networks
Wireless Networks
Home Networks
Internetworks
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Broadcast Networks
Types of transmission technology
• Broadcast links
• Point-to-point links
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Computer networks hardware
Computer networks differ by their size and transmission technology.
There are twp types of transmission technology:
1. Broadcast links
2. Point-to-point links.
Broadcast links have a single transmission channel that is shared by all the
computers on the network. If the destination of the sent messages is all the
existing computers on the network this known as a broadcasting. If the
destination of the sent messages is a specific computers this known as a
multicasting.
In Point-to-point networks messages are sent from one sending computer to
one receiving computer.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Computer networks hardware
Basically there are three sizes of computer networks:
Local area network (LAN): A local area network is a network that spans a
small space (like a single building) and provides services to a small number of
people. LAN may have different segments distributed across all building floors..
Metropolitan Area Network (MAN): connects two or more LAN networks
over a specific geographical area ( usually a city ).
Wide Area Network (WAN): A wide area network uses wide variety of resources
are deployed across a large geographic and any available communication lines. The
largest and best example of a WAN is the Internet, which is a network composed of
many smaller networks. The Internet is considered the largest network in the world.
Wireless networks: In wireless network there are no wires between hosts and
servers. The data is transferred over sets of radio transceivers. The most common
wireless networks cover ranges from hundreds of meters to a few kilometers
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
LANs, MANs, & WANs
One early solution was the creation of local-area network
(LAN) standards which provided an open set of guidelines for
creating network hardware and software, making equipment
from different companies compatible.
What was needed was a way for information to move
efficiently and quickly, not only within a company, but also
from one business to another.
The solution was the creation of metropolitan-area networks
(MANs) and wide-area networks (WANs).
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Broadcast Networks (2)
Classification of interconnected processors by scale.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Physical topology of computer networks:
The physical topology of a network refers to the configuration of
cables, computers, and other peripherals.
The following slides discuss the physical topologies used in
networks and other related topics.
•Linear Bus
•Star
•Ring
•Mesh
•Hybrid
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Local Area Networks
Two broadcast networks
(a) Bus
(b) Computer
Ring Networks, Fifth Edition by
Andrew Tanenbaum and David
Physical Topologies
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Linear Bus topology:
In linear bus computers are connected to a common line of information and this
common line is called a bus, so it is called a bus topology. A linear bus topology
consists of a main run of cable with a terminator at each end . All computers are
connected to the linear cable.
A bus topology uses a single backbone cable that is
terminated at both ends.
All the hosts connect directly to this backbone.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Fig.1 Linear bus topology
Advantages of a Linear Bus Topology
•Easy to connect a computer or peripheral to a linear bus.
•Requires less cable length than a star topology.
Disadvantages of a Linear Bus Topology
•Entire network shuts down if there is a break in the main cable.
•Terminators are required at both ends of the backbone cable.
•Difficult to identify the problem if the entire network shuts down.
Computer Networks,
Fifth
Edition
•Not meant to be used as a stand-alone
solution
in a
largebybuilding.
Andrew Tanenbaum and David
Star topology :
A star topology is designed with each node (file server, workstations, and
peripherals) connected directly to a central network hub
Data on a star network passes through the hub before continuing to its
destination. The hub or concentrator manages and controls all functions
of the network.. This configuration is common with twisted pair cable;
however, it can also be used with coaxial cable or fiber optic cable.
Fig. 2. Star topology
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
A star topology connects all cables to a central point of
concentration.
Advantages of a Star Topology
•Easy to install and wire.
•No disruptions to the network then connecting or removing devices.
•Easy to detect faults and to remove parts.
Disadvantages of a Star Topology
•Requires more cable length than a linear topology.
•If the hub or concentrator fails, nodes attached are disabled.
•More expensive than linear bus topologies because of the cost of
the concentrators.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Ring Topology
All computers in the network are connected in a closed loop. The ring
topology is actually a logical ring, meaning that the data travels in circular
fashion from one computer to another on the network. It is not a physical
ring topology.
The advantage of this topology is that every computer in the ring gets equal
opportunity to send its data, and no computer can dominate the network.
This also leads to the slow performance of the network, when more
computers are added. In this topology, if one computer fails, the entire
network goes down. Its troubleshooting is difficult, and addition or removal
of any computer can disrupt the entire network.
A ring topology connects one host to the next and the last host
to the first.
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This creates a physical
ringNetworks,
of cable.
Andrew Tanenbaum and David
Fig. 4 Ring topology
Advantages of Ring topology
Cable faults are easily located, making troubleshooting easier
Ring networks are moderately easy to install.
Disadvantages of Ring topology
Expansion to the network can cause network disruption.
A single break in the cable can disrupt the entire network
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
.Mesh
topology :
In a mesh topology, each computer on network has redundant data
paths to other computers. The mesh topology provides fault tolerance-
if a wire, hub, switch, or other component fails, data can travel along an
alternate path.. A mesh topology is most often used in large backbone
networks in which failure of a single switch or router can result in a
large portion of the network going down
A mesh topology is implemented to provide as much
protection as possible from interruption of service.
Each host has its own connections to all other hosts.
Although the Internet has multiple paths to any one
location, it does not adopt the full mesh topology.
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Advantages of Mesh topology
• Mesh networks are "self-healing" - if a node goes down the data takes
another path.
•Relatively inexpensive to cover a large area.
Disadvantages of Mesh topology
•Routing network traffic can be difficult because of all the different
possible paths between nodes.
•No
central
infrastructure
(the
network
connections).
Computer Networks, Fifth Edition by
Andrew Tanenbaum and David
Fig. 5 Mesh topology
relies
on
peer-to-peer
Hybrid topology
Hybrid network is the combination of different topologies such as star,
Ring, Mesh, Bus etc. All the networks of different types (can be
connected together through a central hub (in the form of star network)
as shown in the figure 6.
Fig. 6 Computer
Hybrid topology
Networks, Fifth Edition by
Andrew Tanenbaum and David