Introduction • Communication refers to the transfer of information from one place to another • The simplest communication system consists of the following: Message Receiver Sender Medium
Example Voice TelephoneSet TelephoneSet Telephone Line
Computer Communication In order to allow 2 computers at different location to communicate over a telephone line, a modem is needed to change the data from digital to analog signal and vice versa. Encode Transmission Decode
010110 Receiving device receive analog signal Sending device send digital signal Encode • Information (e.g. data, text, voice or video) from the sending device is converted into signals which the communication medium can carry
Transmission • The signals are transmitted through the medium to the receiving device Signal transmitted by telephone line Sending device Receiving device
010110 Receiving device receive digital signal Sending device send analog signal Decode • The signals are converted back into the information in its original form in the receiving device
Computer Network • One drawback of PC is that it is standalone computer primarily designed for single users. • Information is therefore cannot be shared or transmitted easily and effectively between computer. • The solution is to link up computers to form a computer network.
Computer Network A Network is a collection of computers and peripherals via communication media such as cable and telephone line.
The need for networking Benefits of using network: • Efficient sharing of resources • Centralized control • Communication • Easier software management • Flexibility of location
1. Sharing of resources OK! I give it to you. • Sharing data or program I want your file. Thank you!
1. Sharing of resources OK! I let you print. • Sharing of hardware resources such as printer I want to print.
1. Sharing of resources • Sharing : data, programs and hardware • Data and software can be centrally storedin a computer acting as the file server and accessed by any computer in the network • An expensive laser printer can be connected to a computer which serves as a print server and processing printing jobs from other computers
2. Centralized Control The network supervisor better security measures centralized control over all facilities and resources
2. Centralized Control • The network supervisor can have a centralized control over the use of all facilities and resources • including all data, programs, disk spaces and other hardware • better security measures can be applied
3. Communication Mac IBM PS/2
3. Communication • Different types of computers store data files using different internal representation methods. • A network operation system can automatically convert the files into the required representations before they are transferred.
4. Easier Software Management Server Install new software Use new software Use new software Use new software
4. Easier Software Management • When a new applications is developed and installed in the server, workstation canimmediately use it from any computer • upgrading or changing software is simpler because it is now stored in the single file server but not distributed among different computers
5. Flexibility of location • Any computer on the network can be used to access the centralized database or the software and data in the file server • it is fairly easy to add a workstation anywhere, relocate a computer to another site, to add a new printer or any other resources
Local Area Network (LAN) • Network that connects computer in a limited area, such as an office, a school or group of buildings is called LAN.
Metropolitan Area Network (MAN) • Within a large city • Optical fibers as media
LAN LAN LAN Wide Area Network (WAN) • link small networks in different geographic area
Network Topology It refers to the way by which the network hardware (called nodes) are arranged and the means if data flow.
Star architecture Workstation Workstation Server Workstation Workstation
???? I can’t work! Hello? Star architecture Host Node
Yes, I can hear you Transferring Hello? Star architecture Host Node
Host fails, whole network breaks down Node fails, network not affected Configuration is simple Star architecture
Ring architecture Workstation Workstation Server Workstation Workstation
PC1, I love U! Ring architecture I know u love me, but I hate u ! Oh, not for me, I will pass the message All Computer are nodes
PC1, I love U! Ring architecture ???? Oh, I can’t transfer your message!!
All computers are Nodes If any node fails, whole network break down Ring architecture
Bus architecture Workstation Workstation Server Bus Workstation Workstation
Bus architecture What! The deadline has changed?? Not my message, I won’t pick up Not my message, I won’t pick up It’s my message, I will pick it up Node BUS Not my message, I won’t pick up You have to hand in your homework today!
Bus architecture What! The deadline has changed?? Not my message, I won’t pick up It’s my message, I will pick it up Node What will happen? BUS Not my message, I won’t pick up You have to hand in your homework today!
All Nodes connected to BUS If any node fails, network not affected Bus architecture
Interconnection of LANs Bridge Gateway
Interconnection of LANs • Bridge • responsible for connecting LANs of the same type • Gateway • responsible for connecting LANs of different type
Question Both computer networks and mainframes allow users to communicate and share data and resources. Why computer networks still supersede Mainframes? It is because computer networks have higher reliability and performance over price ratio. It is also much easier to expand a computer network than a mainframe.
Two ways of Transmitting Signal: 1. Direct Mode Transmission Signals are transmitted to a particular receiver
2. Broadcast Mode Transmission Signals are transmitted to all directions
Direct Mode Transmission • Twisted Pair • Cheapest & therefore most common • Susceptible to local electrical noises • Usually used for short distance connections such as telephone line
Coaxial Cable • single wire surrounded by a tube-shaped conductor of solid copper • can support very high speed data transfer • used for long distance communication (e.g. TV system) • moderate cost
Optical Fibre • a popular high bandwidth (can carry thousands of channels) transmission medium • small size,light weight • provide little interference (noise) and highest transmission rate • Suited for long distances communication in high data rate
Broadcast Mode Transmission • Ground station send the data and beam to the satellite by microwave • Satellite will re-transmit data to another ground station
What is Internet? • The Internet is a loose association of thousands of networks and millions of computers across the world that all work together to share information. • “Network of Networks” • The Internet now serves approximately 50 million users! • It is a living entity and is ever growing!