Data Communication IT-402

Data Communication Data Communication Communication Protocol Agenda Data Communication Communication Protocol Forms of data Transmission Data Transmission Mode Types of data Transmission Transmission Media Uses of Communication Technologies

Data Communication Data communication is a process of transferring data electronically from one place to another. Basic elements of data communication are Sender Receiver medium

Elements of data Communication (cont’d) Sender Sender is a device that sends message. The message may be consist of text, numbers, pictures etc. It is also called source or transmitter. Medium Medium is the path that connects sender and receiver. It is used to transmit data. The medium can be a copper wire, a fiber optic cable, microwave etc Receiver Receiver is a device that receives message. It is also called Sink. The receiver can be computer, printer, or another computer related device. The receiver must be capable of accepting the message.

Elements of data Communication (cont’d) Message Medium Sender Receiver

Communication Protocol The procedure of data transformation in the form of software is commonly called protocol. This protocol is a set of rules for exchanging information among computer. These protocols define: How the communication channel is established How information is transmitted How errors are detected and corrected

Functions of Communication Protocols The main functions of communication software protocols are as follows Data Sequencing Data Routing Data Flow Error Control

Forms of Data Transmission There are two forms of data transmission Digital Data Transmission Analog data Transmission

Digital Data Transmission Forms of Data Transmission Digital Data Transmission Digital signal is a sequence of voltage represented in binary forms, these signals are in the form of electrical pulses of ON and OFF. Digital signals are faster and efficient, they provide low error rates, high transmission speed and high- quality voice transmission. All data communication between the computers is in digital form. In digital signals high voltage is represented by 1 and low voltage is represented by 0. 

Analog data Transmission Analog Data Transmission Analog signal is a continuous electrical signal in the form of wave, which is known as Carrier wave. Telephone line is the most commonly used media for analog transmission of data. Light, sound, radio and microwave are also examples of analog signals. 

Data Transmission Modes Transmission mode means transferring of data between two devices. It is also called communication mode. These modes direct the direction of flow of information. There are three types of transmission mode. Simplex mode Half Duplex mode Full Duplex mode

Simplex mode Data is transmitted from the sender to receiver only, (eg: from a central computer to a dumb terminal). The communication can only take place in one direction and it is not possible for the receiver to send data back. An example of simplex transmission would be data being sent to an electronic notice board such as those found in train stations and airports.

Half Duplex mode Data can travel in both directions but not at the same time. Each end of the communications link acts as sender and receiver, (eg: two-way communication between computers and other computers that may be connected to a hub). Controls will exist to ensure that the devices do not send at the same time. One human example of this type of communication is the use of walkie-talkies, where each person communicating must indicate when they have finished speaking.

A telephone is full-duplex device. Full duplex mode Data can travel in both directions simultaneously, (e.g: two or more computers connected to a network device such as a switch that provides full duplex activity). A telephone is full-duplex device. Full duplex mode is a faster way of data transmission as compared to half duplex.

Types of Data Transmission Asynchronous Transmission Synchronous Transmission

Asynchronous Transmission In asynchronous the transmission of data is generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data from the communication symbols is encoded within the symbols. The most significant aspect of asynchronous communications is that data is not transmitted at regular intervals, thus making possible variable bit rate. And that the transmitter and receiver clock generators do not have to be exactly synchronized all the time.

Application Asynchronous activities take place outside of real time system. As asynchronous does not require a constant bit rate. For examples file transfer, email and the World Wide Web. Drawback Overhead of start and stop bits. Asynchronous transmission is relatively slow due to the increased number of bits and gaps.

Synchronous Transmission In Synchronous the transmission of data is sent in a continuous stream at a constant rate. Synchronous communication requires that the clocks in the transmitting and receiving devices are synchronized running at the same rate. so the receiver can sample the signal at the same time intervals used by the transmitter. No start or stop bits are required. For this reason synchronous communication permits more information to be passed over a circuit per unit time.

Over time the transmitting and receiving clocks will tend to drift apart, requiring resynchronization. Synchronous communication is direct communication that occurs in real time. That take place face-to-face, and as technology has evolved, can take place irrespective of distance (ex. telephone conversations and instant messaging)

Application Drawback Most common use is in the ASCII terminals. High speeds communication links established using synchronous modems. Drawback The clock frequency should be same at both the sending and receiving ends. No tolerance in clock frequency is allowed.

Transmission Media Guided Media Unguided Media Guided Media (Wired) Guided media, which are those that provide a conduit from one device to another, includes Twisted pair Cable Coaxial Cable Fiber Optics

Two types of Twisted Pair Cable Guided Media Twisted Pair Cable The wires in Twisted Pair cabling are twisted together in pairs. Each pair would consist of a wire used for the +ve data signal and a wire used for the -ve data signal. Any noise that appears on 1 wire of the pair would occur on the other wire. Twisted Pair cables are most effectively used in systems that use a balanced line method of transmission. Two types of Twisted Pair Cable STP (Shielded Twisted Pair) UTP (Un shielded Twisted Pair)

Guided Media Coaxial Cable Coaxial Cable consists of 2 conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield. An insulating protective coating called a jacket covers the outer conductor. The outer shield protects the inner conductor from outside electrical signals. The distance between the outer conductor (shield) and inner conductor plus the type of material used for insulating the inner conductor determine the cable properties or impedance. The excellent control of the impedance characteristics of the cable allow higher data rates to be transferred than Twisted Pair cable.

Fiber Optics Guided Media Optical Fiber consists of thin glass fibers that can carry information at frequencies in the visible light spectrum and beyond. The typical optical fiber consists of a very narrow strand of glass called the Core. Around the Core is a concentric layer of glass called the Cladding

Unguided Media Unguided media transport electromagnetic waves without using a physical conductor. This type of communication is often referred to as wireless communication Types are Radio Wave Microwave Infrared

Radio Waves: Unguided Media Radio waves are used for multicast communications, such as radio and television, and paging systems. They can penetrate through walls. Highly regulated. Use Omni directional antennas

Microwaves Unguided Media Microwaves are used for unicast communication such as cellular telephones, satellite networks, and wireless LANs. Higher frequency ranges cannot penetrate walls. Use directional antennas point to point line of sight communications.

Unguided media Infrared Infrared signals can be used for short range communication in a closed area using line-of-sight propagation. Low frequency Wireless mouse, keyboards etc

Uses of Communication Technologies The uses of communication technologies are as follows Voice Mail Fax E-Mail Instant Messaging Newsgroups Internet Telephony Video Conferencing Collaboration Groupware Chat Rooms Global Positioning System

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