Communication means the exchange of information or messages. The process of transferring data from one location to another is called Data Communication. In this process, data is transmitted electronically from one location to another by using standard methods.
Today, computer networks are commonly used for data communication. For this purpose, we use cables, telephone lines, computers, and wireless devices that are linked in a network.
Types of Data Transmission: Therefore, data transmission is divided into:
(i) Analog data transmission.
(ii) Digital data transmission.
(i) Analog Data Transmission:
The transfer of data from one place to another in the form of analog signals or in the form of continuous waves is called analog data transmission. The analog signal consists of a continuous electrical wave. The light waves, sound waves or radio waves are examples of analog signals.
(ii) Digital Data Transmission:
The transfer of data from one place to another in the form of digital signals is called digital data transmission. A digital signal consists of individual electrical pulses that represent bits grouped together into bytes. Computer accepts and processes data in the form of digital signals. Data is also transmitted from one computer to another through telephone line, microwave system and satellite. In this system, a modem is used on both sides. A modem is an electronic device that can convert the analog signal into digital and vice versa.
Characteristics of Communication System: The communication system depends upon the following fundamental characteristics.
Delivery: The data must be delivered from source device to the correct destination device.
Accuracy: The data must be delivered accurately, If there is any error occurred during transmission, the data must be re-transmitted.
Timeliness: Data must be delivered within time. It is very important in real time systems because data becomes useless if it is delivered late. For example, in television transmission, the video signals must be delivered within time as they are produced without any significant delay. This kind of delivery is called real-time transmission.
Elements of Communication System: The basic elements of a communication system are:
Message: The message is the information or data that is to be communicated. It may be in the form of text, numbers, pictures, sounds, videos or any combination of these.
Sender: A device that is used to send or transmit messages to another device is called Sender. It is also called Transmitter or Source. A sender may be a computer, workstation, telephone handset, video camera and mobile phone.
Medium: The path through which data is transmitted (or sent) from one location to another is called transmission medium. It is also called communication channel. It may be a wire, or fiber optic cable, or telephone line etc. If the sender and receiver are within a building, a wire is used as the medium. If they are located at different locations, then a medium may be telephone line, fiber optics, microwave or satellite system.
Receiver: A device that is used to receive messages from another device (sender) is called Receiver. It is also called Sink. A receiver may be a computer, workstation, telephone handset, mobile phone, television set, printer, fax machine, and so on.
Protocol: A set of rules that guides (or governs) data communication is called protocol. It represents an agreement between the communicating devices. Without a proper protocol, the devices may be connected but they cannot communicate with each other. For example, a person whose mother language is English cannot communicate with a person who can speak only Swedish.
Today, all type of computers and mobile devices serve as senders and receivers in communication system.
Types of Communication Networks:
In File-Server computer network, a powerful computer having disk with large storage capacity and processing power is installed as central computer. This central computer is known as File-Server, Network Server, Application Server or simply a Server. A File-Server stores and manages files. The data files and software are stored on the Server. The individual computers on a network, called nodes, access the data files and software on the Server. It means that, the File-Server is used to store files and to forward them to nodes that request for them.
Client/Server model is the most popular network model. It is also known as dedicated server model. In client/server network (or arrangement), a powerful computer is used as server. The server controls the functions of network. In addition to control the network, the server also provides a centralized storage area. The software and databases are stored on the server. Different nodes or computers connected to the network can access these software and databases.
All computers (other than computer server) connected in the network are called clients. The clients send requests to the server. Server receives the requests from clients and takes proper actions on these requests. It means that processing is usually done by the server. The results of processing are sent to the clients. Client/Server network may be LAN or WAN.
For example, in a Client/Server network, a database is stored on the Server and the Client computers access the database. The Server portion of the DBMS (Database Management system) is stored on the Server that allows the Clients to add information in database or extract information from database. Similarly, the client portion of DBMS is stored on each Client computer through which request is sent to the Server to access the database. The Server processes the data and sends the result-to the Client computer.
The client/server network has the following advantages.
It reduces the volume of data traffic on the network.
It allows faster response at each node.
It allows using less expensive computers as clients because most of the work is done by server.
The main disadvantage of this network is that the entire network is affected if there is any problem in the server computer.
In peer-to-peer (P2P) arrangement, all nodes (or computers) on the network have equal status. No one has control over others. It means that there is no central computer to control other computers on the network. Each computer stores files on its own storage devices and has its own peripheral devices. The users can share each other's data and devices (or resources) as and when needed. For example, a printer attached with any computer can be used by all computers connected in the network.
Peer-to-Peer network is used in small offices or schools, where primary purpose of the network is to share storage and printers. A Peer-to-Peer network can also include a Server. In this case, a Peer-to-Peer local area network is similar to a File-Server network.
The main advantages of peer-to-peer model are:
It is useful in small offices.
It is easy to design and to maintain.
The main disadvantages of peer-to-peer model are:
It becomes slow under heavy use.
It does not provide the security to protect the data stored on computers connected in the network.
Hybrid Network Model:
The hybrid network has combined features of both client/server and peer-to-peer network (or arrangements) models. It also has a server. The users can share the data and software. Similarly, each node can store its own files, programs, and has its own peripheral devices. The users can also share each other's data and devices. These are the main advantage of hybrid arrangement.
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Imran Zafar writes articles about computer basics and
database management such as basics of computer
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