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Computer Networks
What is a Computer Network?
A network is a collection of computers connected
to each other. The network allows computers to
communicate with each other and share
resources and information.
The Advance Research Projects Agency (ARPA)
designed "Advanced Research Projects Agency
Network" (ARPANET) for the United States
Department of Defense. It was the first computer
network in the world in late 1960's and early
1970's.
What is a Protocol
• A protocol is a system of rules that define
how something is to be done.
• In computer terminology, a protocol is
usually an agreed-upon or
standardized method for transmitting data
and/or establishing communications
between different devices.
Types of Networks
Most Commonly known types are:
• Local Area Network (LAN)
• Wide Area Network (WAN)
• Metropolitan Area Network (MAN)
LAN (Local Area Network) / Ethernet
A network is said to be Local Area Network (LAN) if it is confined
relatively to a small area. It is generally limited to a building or a
geographical area, expanding not more than a mile apart to other
computers.
LAN configuration example:
o
Servers
o
workstations - computers connected to the servers
o
Cables - used to connect the network interface cards in each
computer.
WAN (Wide Area Network):
• A WAN (Wide Area Network) connects multiple
LANs to one another over great geographic
distances, the size of a country or continent.
• The speed available on a WAN varies
depending on the cost of the connections (which
increases with distance) and may be low.
• WANs operate using routers, which can
"choose" the most appropriate path for data to
take to reach a network node.
MAN:
A network spanning a physical area larger
than a LAN but smaller than a WAN, such
as a city. A MAN is typically owned an
operated by a single entity such as a
government body or large corporation.
Benefits of Networks
• Resource Sharing. Resources such as, printers, fax
machines and modems can be shared.
• Centralized Software Management. Software can be
loaded on one computer (the file server) eliminating that
need to spend time and energy installing updates and
tracking files on independent computers throughout the
building.
• Flexible Access. Access their files from computers
throughout the firm.
• Electronic Mail. E-mail aids in personal and
professional communication. Electronic mail on a LAN
can enable staff to communicate within the building
having not to leave their desk.
Disadvantages??
Network Topologies
Topology can be understood as the shape
or structure of a network.
• Physical topology refers to the physical
design of a network including the devices,
location and cable installation.
• Logical topology refers to how data is
actually transferred in a network as
opposed to its physical design.
Three basic topologies are:
• Bus Topology
• Star Topology
• Ring Topology
Bus Topology
• Each node is connected to a single cable
• A signal from the source travels in both
directions to all machines connected on
the bus cable until it finds the intended
recipient.
• inexpensive to implement, hard to
manage.
Star Topology
• Host is connected to a central device with
a point-to-point connection.
• All traffic that traverses the network
passes through the central device, where
it acts as a repeater.
• An advantage of the star topology is the
simplicity of adding additional nodes.
• Disadvantage ????
Ring Topology
• set up in a circular fashion in which data
travels around the ring in one direction and
each device on the right acts as a repeater
to keep the signal strong as it travels.
Internet
•
It is a network of networks that consists of millions of
private, public, academic, business, and government
networks, of local to global scope, that are linked by a
broad array of electronic, wireless and optical networking
technologies.
• The Internet carries an extensive range of information
resources and services, such as the interlinked hypertext documents of the World Wide
Web (WWW) and the infrastructure to support email.
• The Internet is often used as an example of a
successful protocols-based system in which the
implementation of key qualities of protocols, such as
error correction and message formatting, are utilized and
respected
across
a
wide
variety
of hardware and software.
Bandwidth
A rate of data transfer, bit rate or throughput,
measured in bits per second (bps)
• Web Caching (Storing web page locally)
• Content Distribution Network ( is a large
distributed system of servers deployed in multiple data
centers in the Internet. The goal of a CDN is to serve
content to end users with high availability and high
performance)
• P2P (refers to a computer network in which each
computer in the network can act as a client or server for
the other computers in the network, allowing shared
access to files and peripherals without the need for a
central server.)
OSI Reference Model
The ISO has developed a seven layer
open system Interconnection model to
serve as a standard model for network
architecture.
Typical Networking Devices
• Repeater. Operate at Layer 1 of the OSI
• Hubs. Allow the interconnection of nodes and
create a physically attached network.
• Bridges. Passes data frames between
net-works using the MAC (Media Access
Control) address (Layer 2 address).
• Switches. Allow simultaneous communication
between two or more nodes, at a time.
• Routers. Passes data packets between
connected networks, and operate on network
addresses (Layer 3 address) .
Wireless Networks
• It is the transmission of data from source
to destination without the use of wires as
the physical media.
• Do not require messy wires as a medium
of communication, they can be used to
connect far-off places.
• cheaper than wired networks specially in
the case of long-distance communication.
• pretty effective and fast, especially with
the modern advancements in this field
Wireless Concerns
•
•
•
•
Cost And Speed
Quality of Transmission
Frequency Allocation (Licensed & unlicensed)
Others ??
Network Security
•
consists of the provisions and policies
adopted by a network administrator to
prevent and monitor unauthorized access,
misuse, modification, or denial of
a computer network and networkaccessible resources.
• Network Management (Firewalls, AntiViruses, Authentications etc)
CASESTUDY:
Celanese Chemicals & Others:
(Wireless Business Applications)