Week 2: Data Communication

What is data?

• "raw data" that had been processed, arranged, stored and will be used to get information.

What is data communication?

• Process of change/ transfer information in a form of a digital data (binary) in between two or more devices using electronic delivery system.
• Data communications is transmitted via mediums such as wires, coaxial cables, fiber optic, or radiated electromagnetic waves such as broadcast radio, infrared light, microwaves, and satellites.

Type of Signal

• Analogue Signal
• Analogue Signal- is like the human voice. Formed by continuously varying voltage level that create wave than be grasped by an analogue transmitter like microphone. Typically presented by their characteristic sine wave.
• Analogue signal is transmitted through PSTN line such as phone line.
• Involves 2 parameters: Frequency and Amplitude

• Frequency: Number of completed wave's cycles. Measured in Hertz (Hz), which is cycle per second.
• Amplitude: Wave's height that measured in voltan  (V) or decibel (dB). A strong signal will create higher amplitude.
• Digital Signal
• Refers to an electrical signal that is converted into a pattern of bits. Unlike an analog signal, which is a continuous signal that contains time-varying quantities, a digital has discrete value at each sampling point. The precision of the signal is determined by how many samples are recorded per unit of time.

Data Transmission Mode

• Parallel Transmission
• Data is sent at least one byte at a time, each bit in the byte taking separate path.

• Serial Transmission
• The process of sending data one bit at a time, sequentially, over a communication channel or computer bus. A bit slower compared to parallel transmission.

3 Serial Transmission Modes

• Synchronous Transmission 
• is a data transfer method which is characterized by a continuous stream of data in the form of signals which are accompanied by regular timing signals which are generated by some external clocking mechanism meant to ensure that both are sender and receiver are synchronized with each other.

• Asynchronous Transmission 
• is the transmission of data in which each character is a self- contained unit with its own start and stop bits an uneven interval between them and it also referred to as start/stop transmission.

• Isochronous Transmission 
• Data is sent at the same time as other related data to support certain types of real time applications. For example streaming voice, video and music.

Directions/ Flow of Data Transmission

• Simplex
• One way communications/ one directions. Role of transmitter and receiver are fixed. For example, radio station- transmits the signal to its listener and listener never allows listener transmitting back.
• Half Duplex
• Flow in 2 direction but never at the same time. One station transmits information to another station without any interruption. The other station will response after that transmission has been completed. For example, Walkie-talkie.
• Full Duplex
• Data can moves in both directions at the same time. Both station can transmit and receive simultaneously. Consists of two simple channels; 1 channel, linking at the same point. For example, Telephone.

Data Compression