Introduction to Computers Lecture# 5 Data Communication and Networks.

Introduction to Computers

Lecture# 5

Data Communication and Networks

What’s a Network? a network: consists of two or more computers that

are connected together to share information.

Information Society : is a society in which every thing in the human life depends upon using the computers to exchange information

Information Superhighway : The very high speed of exchanging information .

Data Communication Data Communication: a data distribution (text,

sounds or images or moving pictures) between two or more points(computers).

An important requirement of the information society is the facility to transfer data to remote locations quickly and conveniently.

Data is transferred in the form of 0 or 1, after converted from its original form by a global codes such as ASCII.

Data Communication The competition between communication

companies has led to a lowering charges and the expanding of services.

Now, you can use a mobile phone to access Internet .

Internet access itself is being offered either free of charge in join-up or monthly charges.

Workgroup ComputingMeans that the user at a network can use his own computer to do his task .

Benefit of this technique are:Sharing files, Documents and resourcesSharing softwareSharing Equipment's.Providing services Efficiently.Sending messages to all the people in the network at the same time ,accessing the same file and updating it by any one who has the authority to do it.

Network Types

Networks can be classified according to: Geographical Distance:

1) LAN (Local Area Network) Client / Server Network Peer-to-Peer Network2) WAN (Wide Area Network )

Topology

Network Types (According to their Geographical Distance) 1) LAN (Local Area Network)

It is the number of computers that are linked together by cables in a limited area (a building or group of nearby buildings).

LAN might be : Client / Server Network Peer-to-Peer Network

Types of Network : (LAN) Client/ Server Network

Where there is a specific computer called a Server which saves all common files and documents,

so that other computers (Clients) can use, access, update and manipulate them at the same time.

Other kinds of servers are: Print Server, Communication Server and File Server.

Peer- To-Peer Network Does not use a server. Individual computers share data directly with others

computers. It is less expensive then Client/Server network.

Network Types (According to their Geographical Distance) 2) Wide Area Network (WAN)

Computers and Computer Networks are linked together over a large area. Many WANs use satellite communications or Telephone network. WAN is used to connect offices of an organization that are located in different cities in the same country or in different countries. As an example:WAN used to connect the Bank ATM. The largest WAN is : the Internet.

Types of Networks according to their Geographical Distance LAN vs. WAN

Peer-to-Peer LAN

Client-Server LAN

WAN

Switch)

Hub

Router

Repeater

Bridge

WAN’s Hardware

WAN’s Hardware

Hub: a distributer that has a lot of ports to connected to computers.

Switch: like a Hub, but it transmits packet to destination directly.

Router: choose the best path for transmission the packet . Bridge: connect two similar LANs Gateway: connect different LANs Repeater: repeat signals that travels via long distance.

Multiplier: combine messages of several devices and send them along a signal high speed path .

Network Topologies:Star Network

Ring Network

Bus Network

1- Star Networks A network in which all microcomputers and other

communication devices are connected to a central hub.

Any communication between stations on a star LAN must pass through the central node.

The central node controls all the activities of the nodes.

Advantage is, the hub prevents collisions between messages.

Disadvantage is, if a connection is broken, the entire network stops working.

Network Topologies:

2- Ring Networks A network in which all microcomputers and other

communication devices are connect in a continuous loop.

In this topology data is transmitted in one direction only. Thus the data packets circulate along the ring in either

clockwise or anti-clockwise direction. Electronic messages are passed around the ring until

they reach the right destination. Advantage is , messages flow only in one direction so

there is no danger of collision. Disadvantage is , if a connection is broken between any

station, the rest of the devices on the network will not continue operating.

Network Topologies:

3- Bus Networks All communication devices are connected to a

common channel (the bus). Advantage : If one devices of the topology fails it

does not affect the entire system. Disadvantage is :o The disadvantage of bus topology is that any

break in the bus is difficult to identify.o the extra circuitry and software are needed to

avoid collisions between data.

Network Topologies:

Communication Hardware

Communication HardwareTo control data transmission through Networks and Internet , the following is considered:

1- A Modem (Modulator/Demodulator) Used to send the data over phone line . Modulation : Convert digital signals (used in computer)

into analog form (used in telephone network) . Demodulation :convert analog signal back to digital signal.

Baud rate : the speed at which data is transmitted , measured in bits per second (bps).

Fax Modem : modem with fax capability . Send signals directly from your computer to someone else’s fax machine or computer fax modem .

Communication Hardware 2- Leased Line :

Is a communication line that is used for one customer . The user pays a flat rate for its use ,no matter how many calls

are made . It is always available to the user who leased . The quality of transmission is superior . leased lines need to a special device similar to the modem

Integrated Services Digital Network (ISDN): Is designed to transmit the digital signals with more speed but

with extra cost . A modem is not needed .


2- ADSL (Asymmetric Digital Subscriber Line ): Is a new technology that allow more data to be

sent over the existing copper telephone line. These lines are described asymmetric lines

because the speed receiver or downloading much higher than the transmission.


3- Network CardIs an online panel that demonstrate inside the device on the motherboard.Mission transfer data between devices in the local network.They are implemented protocols.

Communication Hardware 5- Transmission media

Are used to send data over the network . Wired media.o Twisted Pairso Coaxial Cableso Fiber optic

Wireless media .o Radio waveso Microwaveso Satellite

Communication Hardware Wired media.o Twisted Pairs:• Wire (two thin strands of insulated wire twisted together.• Is the transmission medium that has been in use the longest.o Coaxial Cables:• The medium pioneered by the cable television industry.• Was originally developed to carry high-speed,

interference-free video transmissions.o Fiber optic• uses clear glass or plastic fiber strands.• each approximately the thickness of a human hair.• Is transfer data at the speed of light.

Communication Hardware Wireless media .o Radio waves Are the invisible waves used for radio, television and

mobile transmission .o Microwaves Are more powerful waves used in radar

and in microwave ovens.o Satellite Using microwave and satellite on the ground for transport

in extended networks.

Network Protocols It is a set of instructions and procedures that

maintain and control transmission in networks

i.e. the number of computers that can share the link, error correction, transmission speed

Example : 1)Ethernet Protocol 2)TCP/IP Protocol

Network Protocols

The Internet

Definition: A larger expanded computer network covering all over the world up between personal computers and local networks and expanded, and is available for any user to be a member.

It is the Biggest WAN Any computer that has the facilities outlined

above can access it. The user can get a large amount of information

about one subject.

Internet Development1) In the 70’s was the first contact between two computers in the U.S, this system transmits text-only and needs a high degree of computer knowledge.

2) In the 90’s, a simplified way of connecting to remote computers was developed. It is called Hyper Text. You can click on a special text to gain information.

3) After that ,it became possible to transfer graphics, images, sounds and video over the Internet and called this technique the World Wide Web(WWW)

Internet Services Search Engines: Different programs with

different methods that helps you to find

information on The Internet in seconds.

Electronic Mail:• Is a program which enables you to transmit and receive

messages over the Internet. • It can transmit different data formats. You can edit, update

and retransmit the same message. • Also you can transmit the same message to a lot of people

at the same time.

Intranet and ExtranetIntranet: a private network ,it is an internal network used in large institutions to share company information and computing resources among employees .Employees inside company only authorized access to the Intranet.

Extranet: Is an extension of Intranet particular institution so that people who are authorized to access from outside the network to data and applications.Operations are organized and powers to use Extranet by firewalls.

Firewall

Firewall: set of related programs at a network server , help to protect the resources of a private network from users from other networks .