Networking

COMPUTER NETWORKS

WHAT IS A COMPUTER NETWORK

A Computer Network is a group of two or more
independent computers connected in an organized
manner such that they can communicate with each
other .
Computers on a network are sometimes called nodes.

WHY A COMPUTER NETWORK?
The main reasons are:
 Distribute pieces of computation among computers
(nodes)
 Coordination between processes running on
different nodes
 Remote I/O Devices

WHY A COMPUTER NETWORK?

 Remote Data/File Access
 Personal communications (like e-mail, chat,
audio/video conferencing)

Advantages & Disadvantages of Computer
Networks
Advantages:
 Price/Performance Ratio.
 Performance Quality.
 Reliability.
 Accessible Resources.
 Incremental Growth of Computing Power.

contd..

Advantages &Disadvantages of
Computer Networks (contd..)
Disadvantages:
Disk space management.
Resource management.
Network Architecture management.

Characteristics used to categorize different
types of networks:
Area of location: Based on geographical areas
covered as Networks can be divided into : LAN,
MAN,& WAN
Topology : According to the geometric arrangement
of computers the different topologies are BUS,STAR,
RING & WIRELESS

Characteristics used to categorize different
types of networks:

Protocol : The protocol defines a common set of rules
and signals that computers on the network use to
communicate.Some of the popular protocols are
ETHERNET & TOKEN-RING NETWORK.
Architecture : Networks can be broadly classified as
using either a CLIENT/SERVER or PEER-TO-PEER
architecture

LANs : Local Area Networks
 Developed in 1970s.
 Typically connects computer in a single building or
campus.
 Medium : optical fibers, coaxial cables, twisted
pair, wireless.
 Speeds adequate for most distributed systems
 High speed networks (0.2 to 100 Mb/sec).

MANs : Metropolitan Area Networks
 Developed in 1980s.
 Generally covers towns and cities (50 kms)
 Medium : optical fibers, cables.
 Data rates adequate for distributed computing
applications.

WANs : Wide Area Networks
 Developed in 1960s.
 Generally covers large distances (states, countries,
continents).
 Medium : communication circuits connected by
routers. .

WANs : Wide Area Networks
 Problems with delays if using
satellites.
 Typical speed : 20 - 2000 Kbits/s.
 Not (yet) suitable for distributed
computing.

BUS TOPOLOGY

On the bus network illustrated here, the electrical
signal representing the packet travels away from the
sending station in both directions on the shared cable.
All stations will see the packet, but only the station it
is addressed to will pay attention to it.

STAR TOPOLOGY

In a star topology all stations are wired to a central
wiring concentrator called a hub.Similar to a bus
topology, packets sent from one station to another are
repeated to all ports on the hub.

STAR TOPOLOGY

This allows all stations to see each packet sent on the
network, but only the station a packet is addressed to
pays attention to it.

RING TOPOLOGY

The ring topology used in Token Ring networks is a
collapsed ring that looks like a physical star. Each
station is connected to a Token Ring wiring connector
by a single twisted pair cable with two wire pairs.

RING TOPOLOGY

One pair serves as the "inbound" portion of the ring
(also known as the receive pair) and the other pair
serves as the "outbound" or transmit pair.

WIRELESS TOPOLOGY

 Wireless Topology components generally include a PC,
a transmitter/receiver, and a software program loaded
into the PC.
 Wireless Topology is normally very slow compared to
other topologies.
 Wireless LANs are more limited in distance, and
usually work well in large open areas.

Ethernet Local Area Networks

Ethernet is an open network standard developed by
Intel, Digital Equipment and Xerox.
Ethernet is the most common network. It offers
support for a variety of protocols and computer
platforms and is relatively lower in cost.
Ethernet LANs use a bus topology.

Network Medium
Once you have the network cards installed and
interfaced in your computer, you need a way to
connect them to each other.
The network media used can be:
wire ( Bounded) or
wireless (Unbounded).

Network Medium (contd…)
Bounded Media:Wires or network cables are
referred to as bounded media because the signal
travels through a physical media shielded on the
outside (bounded)by some material.Bounded media
are great for LANs because they offer good speed,
good security and low cost.
Examples of bounded media CO-AXIAL,TWISTED
PAIR & OPTICAL FIBER.

Network Medium (contd…)

Unbounded or Wireless media:This does not use
any physical connectors between the two
communicating devices. Usually the transmission
is sent through the atmosphere, but sometimes it
can be just across a room.Wireless media is used
when a physical obstruction or distance blocks the
use of normal cable media.
The three main types of Wireless Media are
radio wave, microwave and infrared.

Coaxial Cable
 Used extensively in LANs.
 Single central conductor
surrounded by a circular
insulation layer and a
conductive shield.
 High quality of data
transmission.
 Max. used data rates : 100
Mbits/s.
 Problems : signal loss at
high frequencies.

Twisted Pair Cable
 Extensively used in
telephone circuits, where
several wires are insulated
and put together.
 Low signal to noise ratio
(cross talk) -> Low data
rate.
 Good for short-distance
communications.
 UTP and 10BaseT are Used
in LANs and have much
higher bandwidth.

Optical Fiber
 High quality and high
bandwidth data
transmission
applications.
 Use light instead of
electric pulses for
message transmission.
 Very high frequency
ranges (20,000 Mhz).
 Single fiber can support
over 30,000 telephone
lines.

Optical Fiber (Contd..)
 Data transmission rates of 400 Mbits/s and more.
 Becoming very popular for MAN and LAN, also
used for intercontinental links.
 High signal to noise ratio, difficulty in tapping
(security).
 Cost is the single biggest drawback (currently).

Wireless Media

 For WANs satellites provide global communication
over the world, receiving signals from transmitters and
relaying them back to the receivers.
 For MANs microwave radio technology is widely used
(2 to 24 Mbit/s).

Wireless Media

 For LANs Spread Spectrum radio technology is
becoming very popular (up to 2 Mbit/s).
 Infrared : Line of sight limitation.

Common Hardware Requirements for
Computer Networking

Common Hardware Requirements for
Computer Networking
NetworkInterface Card : Also known as network
adapter, interfaces a computer board with the network
medium.
Repeater : two-ports electronic device that just
repeats what it receives from one port to the other.
Bridge : a more sophisticated repeater with logic
capabilities that filters packets
contd..

Common Hardware Requirements
for Computer Networking (contd..)
Hub : multi-port repeater.
Switch : multi-port bridge
Router : links two or more networks
(different types too), passing messages with
appropriate routing information. It operates
at OSI level 3.

Common Hardware Requirements
for Computer Networking (contd..)
Modem :Device that converts digital data
originating from a terminal or computer, to
analog signals used by voice communication
networks such as the telephone system
Firewalls : Firewalls are systems that establish
access control policies among networks.

NETWORK INTERFACE CARD
Often abbreviated as NIC,
an expansion board you
insert into a computer so
the computer can be
connected to a network.
Most NICs are designed for
a particular type of
network, protocol, and
media, although some can
serve multiple networks. .

Repeaters

 A communications device that amplifies or
regenerates the data signal in order to extend the
transmission distance.
 Available for both analog and digital signals, it is used
extensively in long distance transmission.

Repeaters

 Repeaters work at layer 1 of the OSI model
 However the amount of Repeaters that can be chained
together is limited

Bridges

•A Bridge is an electrical device which connects and
passes packets between two network segments. In
general, a bridge will forward or discard an incoming
frame based on the MAC address of that frame.

Bridges

Unlike routers, bridges are protocol -independent.
They simply forward packets without analyzing and
re- routing messages.

Hubs

Hub's major function is to replicate data it receives
from one device attached to it to all others.

Hubs

Characteristics :
Hubs come in many flavors. They differ in the amount
of devices that can connect to them, the length of wire
that can transmit on, and the type of media they
support.

Switches

 Switch is a device used to link several separate
LANs and provide packet filtering between them.

Switches

 In effect, it acts like a very fast multiport bridge
packets are filtered by the switch based on the
destination address.
 Switches can also support numerous transmissions
simultaneously.

Routers

 A device that forwards data packets from one local area
network (LAN) or wide area network (WAN) to
another.

Routers

 Based on routing tables and routing protocols,routers
read the network address in each transmitted frame and
make a decision on how to send it based on the most
expedient route (traffic load, line costs, speed,
bad lines, etc.).

Modems

The word "Modem" stands for "MOdulatorDEModulator".
A modem is a device that converts digital data
originating from a terminal or computer, to analog
signals used by voice communication networks such as
the telephone system.
Contd..

Modems

At one end, modems convert the digital pulses to
audible tones and convert audio tones back to digital
pulses at the other.
Contd..

Modems (contd..)
Characteristics :
 Transmission speed
 Internal/External
 Error detection and correction
 Compression

Firewall

 Firewalls are systems that establish access control
policies among networks. They can block information
from entering a network or from getting out of that
network, they can permit different users to perform
different kinds of operations, according to the user's
authorizations.

Firewall

 There are two general types of firewalls: Packet
Level Firewalls and Application Level Firewalls.

Firewall (contd..)
There are two general types of firewalls:
Packet Level Firewalls, which examine
packets and decide according to filtering rules
whether to pass them to the network.
Application Level Firewalls, which monitor
specific applications protocols.