CSCI-235 Micro-Computer Applications The Network

© Prentice-Hall, Inc 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 Sending device Communications link Communications link Receiving device Receiving device

A Communications Model  Source generates data to be transmitted generates data to be transmitted  Transmitter Converts data into transmittable signals Converts data into transmittable signals  Transmission System Carries data Carries data  Receiver Converts received signal into data Converts received signal into data  Destination Takes incoming data 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

© Prentice-Hall, Inc Data Rate and Bandwidth  Any transmission system has a limited band of frequencies  This limits the data rate that can be carried

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

© Prentice-Hall, Inc Modulation Digital Analog Digital Demodulation Modems: From Digital to Analog and Back  Modems are devices that transform signals when sending and receiving transmissions Modulation – Transforming digital signals to analog Modulation – Transforming digital signals to analog Demodulation – Transforming analog signals to digital Demodulation – Transforming analog signals to digital

Networking  Point to point communication not usually practical Devices are too far apart Devices are too far apart Large set of devices would need impractical number of connections Large set of devices would need impractical number of connections  Solution is a communications network

© Prentice-Hall, Inc Circuit switching  Networks create an end- to-end circuit between the sending and receiving computers  Electronic switches establish and maintain the connection Switching and Routing Techniques 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

© Prentice-Hall, Inc AdvantagesDisadvantages Circuit switching Voice and real-time transmission No delivery delays Costly A direct electrical connection between the computers is required Packet switching Efficient, less expensive, and reliable Will function if part of the network is down Delays in receiving packets Not ideal for real- time voice communication Advantages and Disadvantages of Circuit and Packet Switching

© Prentice-Hall, Inc Protocols  Protocols are fixed, formalized standards that specify how computers can communicate over a network

© Prentice-Hall, Inc Network Layers  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 user physical media user physical media receiving sending protocol layer stack

© Prentice-Hall, Inc Reduced hardware costs Reduced hardware costs  Users share equipment Connected people  People can work together without being at the same location  Groupware enables sharing of schedules and communications Advantages of Networking Shared applications  Users share software  File server enables all users to work with the same application program Building information resources Building information resources  Users create common pools of data that can be accessed by employees

© Prentice-Hall, Inc Local Area Network (LAN)  Links computers within a building or group of buildings  Uses direct cables, radio, or infrared signals Types of Computer Networks Wide Area Network (WAN)  Links computers separated by a few miles or thousands of miles  Uses long-distance transmission media

© 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  Network interface card (NIC) – Provides the connection between the computer and the network  Inserted into a computer’s expansion slot Networking Software  Operating system that 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