08.Computer Network - Home - Home

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MODULE 8

Computer Network

Topic


What is network?


Types of Networks


Network Topology


Network Structure


Network Components

Types of Networks


Classified by
network

size
: which specifies how
large an area of the network services may cover.


WAN


MAN


LAN


HAN


PAN

Geographic
range



Connects computers and devices in a
limited geographic
area
, such as one office, one building, or a group of
buildings close together.


The LANs of different offices on a university campus may
also be linked together into a so
-
called
campus
-
area
network
.



Communication network that covers wide geographic area,
such as a country, or the world.



Communication network that covers a city or county.




Use wired, cable, or wireless connections to link a
household’s digital devices


not only multiple computers, printers, and storage
devices but also VCRs, DVDs, televisions, fax machines,
videogame machines, and home security systems.

HAN Capabilities


Share a single high
-
speed Internet connection.


Access files and programs on the other computers in the
house


Share peripherals such as printer, scanner.


Play multiplayer games with players on other computers
in the house.


Lighting control


Thermostat adjustment


Security system


Watering system



Use short
-
range wireless technology to connect an individual’s
personal electronics, such as
cellphone
, PDA, MP3 player,
notebook PC, and printer.


PANs have been made possible with the arrival of such
inexpensive, short
-
range wireless technologies as Bluetooth, ultra
wideband, and wireless USB.

End: Types of Networks


Network Topology

Network Topology


Topology is the layout, or shape, of a network.



Basic topologies are:


Bus


Ring


Star


FDDI


Hybrid

Bus Topology


All communication devices are
connected to a common channel.


All nodes are connected to a
single wire or cable, the bus,
which has two endpoints.


Disadvantage:


If a connection in bus is broken, the entire network may stop
working.


Need
extra software and circuitry to avoid collisions between data
.

Ring Topology


All communication devices
are connected in the
continuous loop.


Use token ring protocol for
data transmission.


Advantage:


No collision because every
messages flow in one direction


Disadvantage:


If a connection is broken, the
entire network stops working.


Star Topology


All computer connect through
Hub.


Advantage:


If a connection is broken, the
rest of devices will continue
operating.


FDDI Topology


Fiber Distributed Data Interface


Uses fiber
-
optic cable with an adoption of ring topology using two token rings


Advantage:


High speed


If one ring fails,

the network still can

continue operating

with the second ring.


Hybrid Topology


Combination of Star, Ring and Bus network.


Eg. Campus network


End: Network Topology


Communications Protocols

Protocol


A communications protocol is an agreed
-
upon
standard for transmitting data between two devices
on a network.


Protocols specify


How devices physically connect to a network


How data is packaged for transmission


How receiving devices acknowledge signals from
sending devices (handshaking)


How errors are handled


And so forth.


Ethernet


Ethernet:
a widely used communications protocol for
LANs


Typically used with LANs that have a bus or star topology
and use twisted
-
pair or coaxial cables.


Version of Ethernet


10Base
-
T : 10 megabits per second


100Base
-
T (Fast Ethernet)


100 Mbps


1000Base
-
T (Gigabit Ethernet)


1
Gbps


10
-
Gigabit Ethernet


10
Gbps


Utilizes a set of procedures (
CSMA/CD
) to send data and
make sure it arrives


CSMA/CD


When transmitting data, an Ethernet network uses a set
of procedures called CSMA/CD, which stand for
Carrier
Sense Multiple Access and Collision Detection
.


When a computer on the network is ready to send a
message, it first “listens” for other messages on the line.


If it senses no messages, it sends one.


If two computer try to send a message at exactly the same
time, so


When a collision occurs, the computer can sense it, and each






before transmitting its message
again.


Collisions and retransmissions are not noticeable to the user.

Token Ring


Token Ring:
Communications protocol usually
used with a ring network topology


Utilizes a
token
to send and retrieve data


Token circulates in one direction


Token is either free or carries a message to be
delivered to a device


Each device checks to see if the message is
addressed to it


Devices can grab a free token and add a
message.

End: Communications Protocols


Network Structure

How networks are structured


Standalone


Host/Terminal


Client/ Server


Peer
-
to
-
Peer


Host/Terminal


Processing and storage are at host side.


Terminal functions input and output operation.


Mainframe is an example of host/terminal.

Client/Server


Clients
-
microcomputers
that request and utilize
network resources.


Servers


computers used to supply
data.


Computers that are
dedicated to processing
client requests.


Servers are typically
powerful computers with
lots of memory and a very
large hard drive.

Different servers manage different tasks


File server


A computer that acts like a disk drive, storing the programs and data
files shared by users on a LAN.


Database server


A computer that stores data but doesn’t store programs.


Print server


Controls one or more printers and stores the print
-
image output from all
the computers on the system.


Web server


Contains web pages that can be viewed using a browser.


Mail server


Manages email.

Client/Server & Host/Terminal



Thin Client


VS

Fat Client


Fat Client


Fat client

-

users provide their own software and
are usually responsible for any upgrades of
hardware and software


Data can be input or downloaded from online
sources
.


Fat Client


Require powerful microprocessor and large amount of
main memory and hard
-
disk to run efficiently


In network: fat client is the client computer that
performs most or all of the application processing, little
work is done by server


Thin Client


Thin client

-

users download not only data
but also different kinds of application
software from an online source


Slimmed
-
down network computer


Low price


Server as terminal or entry point to the online universe


Might not have hard
-
disk because most of software,
and information will be supplied by remote server


Peer
-
to
-
Peer


The word “peer” denotes one who is
equal in standing with another
.


P2P network means all
microcomputers on the network
communicate directly and share
equally with one another

without
relying on a central server
.


Every computers can share files and
peripherals with all other computers on
the network.

Installed & Web
-
Based Software


Installed software is software that is installed on a
PC before it is run.

Web
-
Based Software


Some software is run directly from the Internet as
Web
-
based software.



Advantage of Web
-
based Software


One advantage over installed software is that the
programs and your files can be accessed from any PC
with an Internet connection regardless of the type of PC
or Operating system used.


This makes web
-
based software especially appropriate for
shared scheduling and other communication or
collaboration applications, since documents and other data
can be shared regardless of an individual’s location or
device.


Another advantage of web
-
based software is that the
software may be updated on a regular basis for no
additional cost to the user.


It removes the burdens of installation and maintenance.


End: Network Structure


Components of network

Network Components


Communication media


Computer or other devices with NIC
Card


Network Linking Devices


NOS

Communication Media


Wire


Wireless


Phoneline


Powerline

Cable


Twisted
-
Pair, Co
-
ax,
Fiber optic.


Picture shows the LAN
cable with RJ45
connector.


Wireless


Bluetooth


Wi
-
Fi


Satellite


Phoneline Network


Phoneline
or
Home PNA

standard


Home PNA (Home Phoneline Networking Association)


Allows computers to be networked through ordinary
phone wiring and phone jacks, without interfering with
voice telephone calls


It is quick and easy to set up.


Powerline Network


Allows PCs to be networked over existing power
lines using conventional electrical outlets


Emerging

standard



named


HomePlug

AV

will

also

connect

home
entertainment

devices

(TV, DVD
player
,
stereo

system
)
to

each

other

and
to

the

Internet.


Computer or Other devices


Computer or Other devices


Devices: computer, printer, etc.


Node


Any device that is attached to a network such as
microcomputer, terminal, storage device, printer


Network Adapter


Networking Hardware


Network adapters:

used to connect a PC to a
network


Also called
network interface card

(
NIC
) when in the
form of an expansion card


Come in a variety of formats


PCI


USB


PC Card


Adapter must match the type of network being used
(Ethernet, Wi
-
Fi, Bluetooth, etc.)

Variety of Network Adapter
Configuration

Network Linking Device

Network Linking Device


It is a common connection point or central connection
point for devices in a network.


Hub


Switch


Bridge


Router


Hub


A common connection point for devices in a network.


A place of convergence where data arrives from one or
more directions and is forwarded out in one or more other
directions.


In a hub, a frame is passed along or "broadcast" to every
one of its ports.



A

B

C

D


Each computer can send data
one at a time.


Switch


It can reads the destination address of each packet
and then forwards the packet to the correct port.


Multiple computer can send data multiple channel at
a time.


Total performance is higher than hub



Bridge


An interface which is used to join segments of network together.


Filter the traffic on the network prevent broadcasting over networks.



A

B

D

E

C

F

Network 1

Network 2

Bridge

Hub

Hub

Backbone


A path that links several
networks
together.



Router


A special device that
directs communicating
messages when several
networks are connected
together.


Gateway


A gateway is an interface permitting communication
between LAN and WAN.

Internet

Network Operation System (NOS)


The system software that manage the activity of a
network


It support multiple users to access the network
based on their password and terminal identification


EX:


Novell NetWare,


Microsoft Windows Server,


Unix


End: Components of network