Intro To Data Comm

Data communication Concepts What is Data? – Elements that can be represented by a finite set of symbols, such as digits or alphabets What Is Communication? - Transmission of information between two parties. 4 Basic Elements involved in communication Sender – initiates the communication. Medium – is the mechanism by which the communication is conveyed to the receiver. Receiver – receives the communication. Message – is the information content that is transferred between the sender and the receiver via the medium. (e.g. telephone conversation) Human Communication vs. Data Communication Human communication is richer, less predictable –Words vary in meaning with context –Many factors influence meaning and perception of message Data communication is more precise –Exact replication of information Telecommunication Is a general term for the electronic transmission of information in any type including television, pictures, sound and facsimiles and data in the form of electronic signals or impulses, sent as an individual message between two parties or as a broadcast to be received at many locations. Data Communication Concepts Data Communication is the process of transferring digital information (usually in binary form) between two or more points. Simplified Block Diagram of Data Communication System

Information Source

Transmission Medium

Information Destination

General Description of a Data Communications System A data communications system can be described simply in terms of three components. Transmitter – A transmitter can be any circuit or electronic device designed to send electronically encoded data to another location. Transmitter can also be called as the source. Transmission Path or Channel – A path or a link through which information passes between two devices. In communications, a medium for transferring information also known as a line or a circuit. A communication channel can carry information in many forms such as data, sound and/or video in either digital or analog form. Receiver – In data communications sense, a receiver could be any device designed to receive any conveyed message from the transmitter or the source. (occasionally called as sink) 2 Types of Communication One-way communication - the role of the source and the sink may not interchange. Two-way communication – the source and the sink may interchange roles that is, the same piece of equipment may transmit and receive data simultaneously. Therefore, it is easier to think of a data communication system between point A and B in terms of The Universal Seven-Part Circuit of Data Communication System. The Universal Seven-Part Circuit of Data Communication System

POINT A DTE

POINT B DCE

DCE

DTE–DCE INTERFACE

DTE

DCE–DTE INTERFACE Transmission Channel

1. The Data Terminal Equipment (DTE) at point A 2. The interface between the DTE and the Data Circuit-terminating Equipment (DCE or often Data communication Equipment) at point A 3. The DCE at point A 4. The transmission channel between points A and B 5. The DCE at point B 6. The DCE-DTE interface at point B 7. The DTE at point B

Data Terminal Equipment (DTE) Equipment that constitutes the data source, data sink or both. It includes any piece of equipment (at which communication path begins or ends) or any device that transmits or receives data. Ex. Terminal or PC Data Communication Equipment (DCE) Equipment that provides all the functions required establishing, maintaining and terminating a connection. It also provides signal conversion and coding conversion between DTE and the common carrier’s lines. Ex. MODEMS MODEMS The term MODEM is an acronym for modulator/demodulator. The primary modem function is to convert digital data into analog form, which is suitable for transmission on common carrier circuits. Modulation is the Digital-to-Analog conversion in which the digital is placed on the transmission line by modulation of a tone or carrier. Demodulation is the reverse process. DTE-DCE Interface The DTE-DCE interfaces consist of several input/output circuitries in the DCE and in the DTE, and the connectors and cables that connect them. In most systems, this interface conforms to the RS-232C standard as publish BY Electronics Industries Association (EIA) in the DCE interface.

Closed Systems vs. Open Systems Closed Systems A term used to describe any computer design whose specifications are not freely available. Such proprietary specifications make it difficult or impossible for third party vendors to create auxiliary devices that worked correctly with a closed- architecture machine. Closed systems resulted in the proliferation of proprietary systems where only products coming from the same manufacturers could work. Open Systems A term used to describe any computer or peripheral design that has published specifications. It is designed to incorporate all devices – regardless of manufacturer or model that can use the same communications facilities and protocols. Open systems enable equipment produced by one vendor to be used with equipment from any vendor that complies with the standards. Data Communications Standard Data communications standards or protocols are simply a set of rules that were established for use in the computer industry by the various international bodies. It is concerned primarily with either the internal operation of the computer or the connection of local peripheral devices. Standards Organizations Because of the wide number of hardware manufacturers, a standard is essential in order to connect one computer to another computer if a different type. There are recognized and widely accepted standards governing how data is to be transmitted, whether asynchronously, parallel, or synchronously. Standards govern the format of the data, and also specify the hardware details like voltages to use, bit durations, speeds etc. The major organizations responsible for standards are: • • • • •

Electronics Industries Association (EIA) Made up by manufacturers in the USA. Responsible for RS232 and similar standards. Institute of Electrical and Electronic Engineers (IEEE) Professional organization of engineers. An example is the IEEE-754 standard for representing floating point numbers. American National Standards Institute (ANSI) Represents a number of US standards organizations. Member organizations submit their standards for acceptance. An example is the ANSI standards for representing ASCII characters. Consultative Committee on International Telephone and Telegraph (CCITT) International committee concerned with telecommunications. These standards deal with telephone and data traffic. An example is X.25 International Organization for Standards (ISO) Has standards covering a wide range of computer related topics. The US representative is ANSI. An example is ISO9000 standard for quality assurance.