COMPUTER NETWORKS
Computer Networks A network is two or more computers connected together to allow them to share information and resources. Network connections are created by Cables Radio signals (wireless/wifi) Telephone lines Satellite links (Long distance)
Stand-alone Computer A computer which is NOT connected a network is known as stand-alone computer
Why Use Networks? Easy file sharing To share expensive resources (Hardware) Centralized storage of data Log on to any workstation to access your work. Communicate with other network users (email, IM, video-conferencing) Network software Access to entertainment (Games, video) To use internet services Online shopping Searching for information Online communities
Why Not to Use Computer Network? Computer is vulnerable to hackers If the network breaks works cannot be done Easily be attacked by virus, spreads too.. When we use internet.. Careful about revealing personal information Avoid suspect websites that might contain malware Information found on internet is not accurate or reliable
Why Not Use Computer Network? Slow service- as more users logon to network and request for files, we get a slow network Cost purchasing additional hardware and wiring are expensive Expert support required Network administrators are usually highly-paid
Computers in Network There are two types of computers in a network. Clients or workstation: are normal computers people sit at to get their work done Servers: are special, powerful computers, they provide services to other computers.
Types of Networks Local Area Network (LAN) Wireless Local Area Network (WLAN) Wide Area Network (WAN) Bluetooth (Personal Area Network)
Local Area Network LAN is a small network confined to one room, building or a campus. They are geographically small and use cables or low-power radio (wireless) for the connection.
Wireless Local Area Network A WLAN is a LAN that uses radio signals to connect the computers instead of cables At the centre of the WLAN there is a wireless switch or router with a small antenna It is convenient to use wireless network because it doesn t use long cables all over the building More difficult to secure, other people can also try to connect. Need to use hard-to-guess password
Wireless Local Area Network
Wide Area Network It is a network that extend over a continent or the entire globe. A WAN is often created by many LANS. Constituent computers in a WAN are far apart They often use technologies: Optical fibre, satellite radio links, microwave radio links, etc.
WAN
Bluetooth (Personal Area Network) It is designed for very short-range connections It get rid of the cables Connects computers to its peripheral devices It uses lo-power transmitters and receivers When devices are in range they can be paired
Typical uses of Bluetooth Connecting a keyboard to computer Connecting a wireless mouse to computer Connecting wireless headset with a mobile phone Printing wirelessly from a PDA Transferring data from computer to MP3 player Transferring photos from phone/computer to another devices
Network Topology A network can be made by connecting computers in number of different ways. These different arrangement is called as Topology There are three common topologies: Bus Network Ring Network Star Network
BUS Network In this topology all the computers are connected to a long, central cable.
Advantages (BUS Network) Is cheap to install (Just one long cable) Easy to expand the network
Disadvantages (BUS Network) Can be quiet slow due to data collision Entire network will stop working if there is any break in the cable or a computer is switched off
RING Network In this topology all computers are connected in a circular form
Advantages (RING Network) It is cheap less cable length required
Disadvantages (Ring Network) If a computer fails the entire network fails Troubleshooting is difficult
STAR Network (the most common network topology) In this Topology all the computers are directly connected to a central device called switch/hub
Advantages (Star Network) Is very fast as there is no data collision - each computer has its own cable If a cable or computer breaks the other part of network still continue working
Disadvantages (Star Network) Is quiet expensive Need to buy long cable and central device Will stop working if the central device fails
Hybrid Network Hybrid Network is one that combine two or more of the basic topology.
Network Interphase Card (NIC)
Network Cable Cables are still used in network because they can carry more data per second and more secure
Optical fibre
HUB Connects computers in LAN It is the central device in Star Network
SWITCH Connects computers in LAN Switch is an intelligent device than Hub
ROUTER Router is a network device that connects two or more networks A common use of router is to join home/office network (LAN) to internet (WAN) It can be wireless too
PROXY SERVER A proxy server is a computer setup to share a resource usually an internet connection Proxy servers are often used instead of router
BRIDGE A bridge is a device that links two different parts of a LAN (Router connects LAN and WAN)
FIREWALL A firewall is a device or a piece of software that is placed between your computer/network and the rest of the network.
FIREWALL
MODEM The word MODEM is an abbreviation of MOdulator DEModulator MODEM converts analogue signals to Digital signal and vice versa. A MODEM contain DAC and ADC MODEM 1010110 1010110
INTERNET Internet is a world-wide network Evolved from an experimental network called ARPANET by US in 1960s It connects millions of computers, thousands of businesses, governments, schools, universities, etc.
Internet is Used For View web pages on world wide web (www) Sending and receiving emails Sharing files Making VOIP calls, video-conferencing Playing multi-player games Listening to streaming music and videos E-commerce - buying and selling goods online Online communities
INTRANET Intranet is a network using the same technology as the internet but it is only accessible within an organisation. Intranet is a private network Used by business and other organisations
Typical Uses of Intranet Viewing internal web pages Internal e-mail and Instant Messages Sharing internal Document Internal News Broadcast
Setting up a Small Network One or more switches/hubs Network cables A wireless access point to connect mobile devices A Router to connect your LAN to Internet(WAN) A firewall to protect you Network from hackers Server to manage network storage, resources, access permissions etc. Also setup an account with Internet Service Provider (ISP). And configure the network and devices
Wireless clients Servers Switch Wireless Access point workstation workstation Firewall ISP Router
Network and Data Security
Preventing Unauthorized Access Physical Security Username and Password, fingerprint-reader Firewall Keep log of all attempts to access the system Data Encryption It is a process of converting data into a unreadable code