Data Communication

Data Communications Data communication system components: Message Information (data) to be communicated. Sender Device that sends the data message. A computer, video camera, or any other device that can be connected to network etc. Receiver Device that receives the data message. A computer, a Television, etc. Transmission medium The physical path by which a message travels from sender to receiver. Twisted pair, coaxial cable, optical fiber, radio waves.

Data Communication Modems A device called modem (short for modulator-demodulator) is needed to translate these digital signals into analog signals that can travel over standard telephone lines. In its modulation phase, the modem turns the computers digital signals into analog signals, which are then transmitted across the telephone line. The reverse takes place during its demodulation phase, as the modem receives analog signals from the phone line and converts them into digital signals for the computer.

Uses for a modem File transfer is the process of exchanging files between computers, either through telephone lines or a network. Uploading Downloading

Data Communications Protocol A set of rules that govern the data communication. Without a protocol, devices may be connected but not communicating.

Rules of communications: Protocol Protocol - a set of rules for the exchange of data between a terminal and a computer or two computers Agreement on how data is to be sent and receipt acknowledged

Data Communications Mode Data flow between two devices can occur in 3 ways Simplex The communication is unidirectional (i.e. on one way). One sends and the other only receives. Ex.: Keyboards and traditional monitors, television broadcasting Half-Duplex Each station can both transmit and receive but not at the same time. Ex.: Walkie-talkies Full-Duplex Both stations can transmit and receive simultaneously. Ex.: Telephone network

Data Communications

Coordinating sender and receiver device Sending data to remote location only works if receiving device is ready to accept it Two approaches to keeping devices in step: Asynchronous transmission Synchronous transmission

Asynchronous Transmission Also called start/stop transmission Start bit transmitted at the beginning of each group of bits Stop bit sent at end of each group Data is transmitted one byte at a time

Synchronous Transmission Large block of characters transmitted Data is transmitted block by block or word by word Error-check bits make sure all characters received Much faster, but equipment is more expensive

Communications Media Physical means of data transmission from one place to another Bandwidth is measure of the capacity of the communications link Types of Communications Media 1.Guided Media 2.Unguided Media

Communications Media Guided /Bounded Media: Wire pairs Coaxial cables Communication devices are directly linked with each other via cables or physical media i.e. Wire pairs Coaxial cables Fiber optics Unguided /unbounded /Wireless Media Data is communicated between communicating devices in the form of wave Microwave transmission Satellite transmission