Transcript lecture11
CSCI-235 Micro-Computer Applications The Network Network Fundamentals A computer network consists of two or more computers linked together to exchange data and share resources Communication is the process of sending and receiving messages Communication channels are the paths through which messages are passed Communication devices transform electronic signals © Prentice-Hall, Inc Putting Together a Network Basic Components Sending device Communications link Receiving device © Prentice-Hall, Inc A Communications Model Source Transmitter Carries data Receiver Converts data into transmittable signals Transmission System generates data to be transmitted Converts received signal into data Destination Takes incoming data Simplified Communications Model - Diagram Simplified Data Communications Model Continuous & Discrete Signals Frequency Domain Concepts Signal usually made up of many frequencies Components are sine waves Can be shown (Fourier analysis) that any signal is made up of component sine waves Can plot frequency domain functions Addition of Frequency Components Data Rate and Bandwidth Any transmission system has a limited band of frequencies This limits the data rate that can be carried © Prentice-Hall, Inc Bandwidth Bandwidth is usually used to refer to the data rate (i.e., the amount of data that can be transmitted through a communications channel) Digital bandwidth is measured in bits per second (bps), kilobits per second (Kbps), megabits per second (Mbps), or gigabits per second (Gbps) Low bandwidth is 56 Kbps and high bandwidth is 622 Mbps Modems: From Digital to Analog and Back Modulation Analog Digital Demodulation Analog Digital Modems are devices that transform signals when sending and receiving transmissions Modulation – Transforming digital signals to analog Demodulation – Transforming analog signals to digital © Prentice-Hall, Inc Networking Point to point communication not usually practical Devices are too far apart Large set of devices would need impractical number of connections Solution is a communications network Switching and Routing Techniques Circuit switching Networks create an endto-end circuit between the sending and receiving computers Electronic switches establish and maintain the connection © Prentice-Hall, Inc Packet switching Outgoing messages are divided into fixed-size data units called packets Packets are numbered and addressed to the receiving computer Routers examine the packets and send them to their destination Advantages and Disadvantages of Circuit and Packet Switching Advantages Disadvantages Costly Voice and real-time A direct electrical Circuit switching transmission connection between No delivery delays the computers is required Efficient, less Delays in receiving expensive, and packets reliable Packet switching Not ideal for realWill function if part time voice of the network is communication down © Prentice-Hall, Inc Protocols Protocols are fixed, formalized standards that specify how computers can communicate over a network © Prentice-Hall, Inc Network Layers user layer physical media receiving sending protocol user stack physical media Network architecture is the overall design of a network The network design is divided into layers, each of which has a function separate from that of the other layers Protocol stack – The vertical (top to bottom) arrangement of the layers; each layer is governed by its own set of protocols © Prentice-Hall, Inc Advantages of Networking Reduced hardware costs Users share equipment Connected people Shared applications Users share software File server enables all users to work with the same application program People can work together without being at the same location Groupware enables sharing of schedules and communications © Prentice-Hall, Inc Building information resources Users create common pools of data that can be accessed by employees Types of Computer Networks Local Area Network (LAN) Links computers within a Wide Area Network (WAN) Links computers separated by a few miles or thousands of miles Uses long-distance transmission media building or group of buildings Uses direct cables, radio, or infrared signals © Prentice-Hall, Inc Local Area Networks (LANs) Network access is controlled by a network administrator Users can access software, data, and peripherals LANs require special hardware and software Computers connected to a LAN are called workstations or nodes © Prentice-Hall, Inc LAN Hardware and Software Networking Hardware Networking Software Network interface card Operating system that (NIC) – Provides the connection between the computer and the network Inserted into a computer’s expansion slot supports networking (Unix, Linux, Windows, Mac OS) Additional system software NIC © Prentice-Hall, Inc Peer-to-Peer Networks All computers on the network are treated as equal Users decide which files and peripherals to share Peer-to peer is not suited for networks with many computers Peer-to-peer is easy to set up. Example: home networks © Prentice-Hall, Inc Client-Server Networks Typical corporate networks are client-server Clients send requests to servers for programs and data, and to access peripherals © Prentice-Hall, Inc Wide Area Networks (WANs) WANs are similar to long-distance telephone systems © Prentice-Hall, Inc WAN Applications LAN-to-LAN WANs are used to connect LANs at two or more geographic locations Companies use WANs to connect their branches to one network system © Prentice-Hall, Inc Backbones Backbones, high-capacity transmission lines, are regional, continental, or transcontinental Internet backbones can carry 2.5 gigabits of data per second © Prentice-Hall, Inc