1. Data Communication

2. 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.

3. 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.

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

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

6. 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

7. 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

8. Data Communications

9. 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

10. 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

11. 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

12. 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

13. 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