Lecture 9 (Computer & Communication)

Computer & CommunicationBasic Networking of

Computers

Introduction As the technology improved, it became possible to link together several computers in such a way that users on one system could use the facilities of other systems in the network.The area covered by a network can range from a university campus to many continents.

Data Communication and Computer Network

Data communications refers to the transmission of digital data between two or more computers. A computer network or data network is a telecommunications network that allows computers to exchange data. The physical connection between networked computing devices is established using either cable media or wireless media. The best-known computer network is the Internet.

Why do we need it ? Computer networks can be used for a variety of purposes:• Facilitating communications: Using a network, people can communicate efficiently and easily via email, instant messaging, chat rooms, telephone, video telephone calls, and video conferencing.

• Sharing hardware: In a networked environment, each computer on a network may access and use hardware resources on the network, such as printing a document on a shared network printer.

• Sharing files, data, and information: In a network environment, authorized user may access data and information stored on other computers on the network. The capability of providing access to data and information on shared storage devices is an important feature of many networks.

• Sharing software: Users connected to a network may run application programs on remote computers.

• Information preservation.• Security.

Data communication channels

Data transmission, digital transmission, or digital communications is the physical transfer of data (a digital bit stream) over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optical fibers, wireless-

  communication channels, storage media and computer buses. The data are represented as an electromagnetic signal, such as an electrical voltage, radio wave,  microwave, or infrared signal.

Main components in communication:

• Message: The message is the information to be communicated. Popular forms of information include text, numbers, pictures, audio and video.

• Sender: Device that sends data messages.

• Receiver: Device that receives data messages.

• Transmission medium: physical path by which message travels from sender to receiver.

Transmission LinesTransmission lines can also be classified according to the direction in which data can flow through the lines. There are three classes:

Simplex: A simplex line allows data to flow in one direction only. It is a send only or receive only device. It is like a one way street

Half-duplex: A half-duplex line can send and receive data, but not simultaneously. Thus, at any time, a half-duplex line may be sending or receiving, but not both at the same time.

Full-Duplex: A full-duplex line allows the sending and receiving of data at the same time. It is analogous to a two way street.

Transmission Modes• Simplex

– signals transmitted in one direction•eg. Television

• Half duplex– both stations transmit, but only one at a time•eg. police radio

• Full duplex– simultaneous transmissions

•eg. telephone

Computer network types•A Personal Area Network or simply PAN, is smallest network which is very personal to a user. This may include Bluetooth enabled devices or infra-red enabled devices. PAN has connectivity range up to 10 meters.

•A computer network spanned inside a building and operated under single administrative system is generally termed as Local Area Network (LAN). Usually, Local Area Network covers an organization’s offices, schools, college/universities etc. Number of systems may vary from as least as two to as much as 16 million. Ethernet is a Local Area Network implementation technology which is widely deployed.

Computer network types• A Metropolitan Area Network (MAN) is a large computer network that spans a metropolitan area or campus. Its geographic scope falls between a WAN and LAN.  the larger the city, the bigger the MAN, the smaller a metro city, smaller the MAN. 

• The Wide area network (WAN) covers a broad area which may span across provinces and even a whole country. Generally, telecommunication networks are Wide Area Network.

Network Topologies1. Point to point: Point-

to-point networks contains exactly two hosts (computer or switches or routers or servers) connected back to back using a single piece of cable.

2. Bus topology: in bus topology all device share single communication line or cable. All devices are connected to this shared line.

Network Topologies3. Star Topology: All hosts in

star topology are connected to a central device, known as Hub device, using a point-to-point connection. That is, there exists a point to point connection between hosts and Hub.

4. Ring Topology: In ring topology, each host machine connects to exactly two other machines, creating a circular network structure.

5. Mesh Topology: In this type of topology, a host is connected to one or two or more than two hosts.

Internetwork• A network of networks is called internetwork, or simply Internet. It is the largest network in existence on this planet. Internet hugely connects all WANs and it can have connection to LANs and Home networks. Internet uses TCP/IP protocol suite and uses IP as its addressing protocol. Present day, Internet is widely implemented using IPv4.

• Internet uses very high speed backbone of fiber optics. To inter-connect various continents, fibers are laid under sea known to us as submarine communication cable.

The internet• Internet is widely deployed on World Wide Web services using HTML linked pages and is accessible by some client software known as Web Browsers. When a user requests a page using some web browser located on some Web Server anywhere in the world, the Web Server responds with the proper HTML page.

• Internet is serving many proposes and is involved in many aspects of life. Some of them are:

Web sitesE-mailInstant MessagingBloggingSocial MediaMarketingNetworkingResource SharingAudio and Video Streaming

OSI MODEL• In an internetwork, the communication takes place between two computers according to some rules. The computers follow the OSI layering model to complete the communication with the other end.

• In layered architecture of Network Models, one whole network process is divided into small tasks. Each small task is then assigned to a particular layer which works dedicatedly to process the task only. Every layer does only specific work.

OSI MODEL• Application Layer: This layer is responsible for providing interface to the application user. This layer encompasses protocols which directly interacts with the user. Example: internet explorer.

• Presentation Layer: This layer defines how data in the native format of remote host should be presented in the native format of host.

• Session Layer: This layer maintains sessions between remote hosts.

• Transport Layer: This layer is responsible for end-to-end delivery between hosts.

• Network Layer: This layer is responsible for address assignment and uniquely addressing hosts in a network.

• Data Link Layer: This layer is responsible for reading and writing data from and onto the line. Link errors are detected at this layer.

• Physical Layer: This layer defines the hardware, cabling and wiring, power output, pulse rate etc.

Other Networking terms• IP address: An Internet Protocol address (IP address) is a unique string of numbers separated by full stops that identifies each computer using the Internet Protocol to communicate over a network.

• Ethernet: A system for connecting a number of computer systems to form a local area network, with protocols to control the passing of information and to avoid simultaneous transmission by two or more systems.

• Fiber-optic: Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. It is normally used in WAN communication.

• Switch: A network switch or switching hub is a computer networking device that links network segments or network devices.

• Router: Routers are physical devices that join multiple networks together. Technically, a router is a Layer 3 gateway device, meaning that it connects two or more networks and that the router operates at the network layer of the OSI model.