Transferring Data Around

Networks

• Is a series of computer systems that are linked together so that they are able to share computer power or storage facilities.

• There are three types of computer networks: Local area network, wide area network, and metropolitan area network.

Local Area Network

• LANs are confined to small area.• Usually this small area is within a single

building.

Metropolitan Network

• MANs is a network interconnect users with computer resources in a geographic area or region larger local area networks but smaller than WAN.

• Like large universities.

Wide area Networks

• WANs cover a wide geographical area. • Using WANs computers may be linked

together in different countries, different cities and buildings.

Advantages/Disadvantages of Networks

• Advantages– Expensive peripherals devices can be shared such as laser printers

and scanners.– Messages can be sent between users.– All users can access the same files.– Software can be placed on the server and accessed by several

users which saves money.• Disadvantages

– Wiring can be expensive buying and installation.– If a WAN is used sophisticated and the rental of

telecommunication links makes it very expensive.– If a server breaks down the whole network becomes unusable.

Network Topologies

• Line (or Bus): the data sent to all the devices on the network at the same time. This means that if a terminal not working properly others are not affected.

• Ring Topology: the terminal or other equipment are connected together in acircle. All the computers having the same importance. The main disadvantage in the ring topology is is that if there is a break in any part of the comunication line, then all of the other devices on the network will be affected.

• Star Topology: there is a computer at the center that is used to control the whole of the network. If this machine breaks down, then the whole network breaks down.

Network Topologies

The Bits that make up the Network

• Some parts that can be found in a typical network are given below:

• Software: network software may be part of the operating system such as windows 2008 server, or can be special software for managing the network.

• Cables: connecting cables are usually used to connect devices on a network. These are made of copper wires.

• Connectors: are used to connect network cables to terminals or other devices.

Fiber optics

Adhoc Networks

Data Transmission

• Communication Links : to make the terminal talk to each other there is a need to have communication links may be cables or radio signals or infra signals. Data can be transferred through metal cables such as a telephone wires fiber cables made up of thin strand of glass, where the data transmitted as a series of pulses of light.

Wireless Media

• With wireless media, electromagnetic waves provide the medium on to which data is encoded as a superimposed signal.

• Radio waves: here the data is transmitted as a series of radio waves.

• microwaves: the data is sent contained in a microwaves, mobile telephones are microwaves, satellite are used when transmitting over large distances. The data signal in the form of microwave is beamed up to satellite and the satellite in turn beams it back to the another part of the world.

• Infra-red: signals can only travel a short distance and this limits their use such as TV remote control.

Data Transfer Speed

• Data transfer is measured in Kbits per second which is the speed at which data is transferred between server and terminal. If the data transfer is slow, the user will notice that it takes a lot of time to be connected to the website.

• Download time is the time to transfer a file from the server to the terminal.

Keeping unauthorized people out of network

• A user ID is a number or name that is unique to a person using the network. The system administrator creates the user ID and allocates the file space and access rights. A user ID tells the system administrator who is using the server currently.

• A password is a string of characters that a user or system administrator creates it. Any password is hidden while typing so the other people can not see it.

• Access rights are located to users by the system administrator such as give rights to the user to create or modify a file or just read a file.

• How to add/delete a user• How to give password to a user• How to change the password• How to reset the password• How give permissions read, write, … etc.• How to specify a strong password.• Do not allow any suspected person to physically

use your computer.• Based on the meaning of PC.

Integrated Service Digital Network (ISDN)

• ISDN is a service provided by telecommunication companies which allows the telephone lines to carry digital communication. Instead of modem you use a device called ISDN terminal adapter. Several digital signals can be sent along the same wire, which means that you can surf the net and receive telephone calls or fax messages using one line.

• ISDN can transmit 128 Kbits per second, whereas modem can transmit 32kbits per second .

• ISDN versus modem: modem converts digital to analog and analog to digital. ISDN does not need a modem it uses an ISDN terminal adapter.

Telecommunications

• Many people work from home and send the data to the server using telecommunication services.

• Message sending: there is a standard for the connection of PCs which enable the computers. This is called open system interconnection (OSI) and also we have TCP/IP

Protocols and Handshakes

• Protocols is a set of rules that should be followed for computer communication. Protocols ensure that each computer behave predictably and provides information in an understandable way.

• A gateway translates the protocols between computers so that different computers are able to communicate with each other.

• A handshake is an exchange of signals which establish the communication between devices

File Compression in Networks

• File compression is the process of condensing the information. It is used when sending data through a telecommunication link. The file compression performed by the software such as winzip, winrar, 7zip … etc

• Also we use hardware to compress the audio/video file. And save them in compressed format like mpeg(1,2,3).

• All these compression algorithms is used to decrease the size of the transmitted file over the network lines to:– Decrease the bandwidth utilization– Save money if you are using dial-up connection– Increase the reliability of the network lines by decreasing

the error rates.• Network speed depends on the following factors– Type of the modem used– Cabling (link type) – Bandwidth

• Bandwidth determines how fast the connection will be.

• Bandwidth determined by the medium through which the data is transmitted.

• Ordinary wire cable like that use the telephone line has lower bandwidth than fiber optic cable.

Cost associated with networking

• Cost of installation of network includes:– Terminal cost .– Server cost– Cabling cost– Modem/ISDN cost– Software cost – ISP ( Internet Service Provider) cost– Backup devices – Telecommunication charges– Connectors cost– Trained people cost ( network administrators and technicians)

• Technical people use the data rate to refer to the rate of rate per second at which data is electronically transmitted across a network line.

• On the internet most of the people measure the data rate based on the kilobits per second.– Example 28.8 modem has a bandwidth capacity

of 27 kilobits per second.

Electronic Data Interchange

• Many companies are using a system called electronic data interchange, which links them to their banks so that they can make immediate payments to their suppliers electronically

• Assignment – Read page 115-126

Security Recommendations for using IMs

• Do not login from others (friends) systems to your IM.

• Do not give your original password when you login.

• Use the shift + backspace while typing your password.

• Be careful from fake messengers and fake websites.

• Do not trust any body