Data Communication

Data Communication is the process of transmission of data from one point to another. The system that transfers data from one point to another is called data communication system or networks.

Element of Data Communication:

1. Sender
2. Communication Software
3. Channel
4. Signal
5. Receiver

Data Communication Signal

Analog Signals

Analog means continues i.e. analog signal is a continuous wave form which changes smoothly time to time. The uses of analog signals are mostly found in telephone lines. The units used to measure these signals are volt and meters.

Digital Signals

In Digital Signals there are many defined points on which these signals travels. Unlike analog signals it is not continuous in nature. For example – pressing the switch indicate one point and again pressing the switching which is of the one and off status. There one bit data represent on status and high signals and the other bit data represent low and off signals.

Data Transmission

Data transmission is the movement of information’s using some form of representation which includes:

• Electrical Signals
• Optical Signals
• Electromagnetic Waves

Data transmission can be of two types: –

The transmission of binary data across a link can be accomplished either on parallel mode or serial mode. In parallel mode multiple bits are sent with each clock pulse. But in serial mode one bit is sent with each clock pulse.

Parallel

All bits of a byte are transferred simultaneously on separate parallel wires. Parallel data transmission is less common but faster than serial transmission.

Serial

Serial data transmission implies transfer data transfer bit by bit on the single (serial) communication line. Serial data transmission is slow as compared to parallel transmission.

Serial transmission occurs in one of two ways –

1) Asynchronous 2) Synchronous

COMMUNICATION TYPES

Directions of Transmissions flow or Data Communication Modes:

There are three modes of Data communication –

Simplex

If transmission is simplex, Communication can take place in only one direction. A device connected to such a circuit is either a send-only or receive-only device. This is rarely used because the sender will send the data and never know that it is received or not.

Half-Duplex

A half-duplex system can transmit data in both directions, but only in one direction at a time. It requires two wires. The terminal might transmit data and then computer responds with an acknowledgement.

Full Duplex

A Full-duplex system can transmit data in both directions simultaneously.

Types of Modulation

Modulation is the process of superimposing digital data on analog waves. There are three forms of Modulation.

Amplitude Modulation (AM)

Two binary values (0 and 1) of digital data are represented by two different amplitudes of the carrier signal

Phase Modulation (PM)

Two binary values of digital data represented by the shift in phase of the carrier signal.

Frequency Modulation (FM)

Two binary values of digital data are represented by two different frequencies, keeping phase and amplitudes constant.

Communication Channel / Media

In any communication network channel or media is a physical or nonphysical path that according transmits data form one point to another.

In network two types of media available for communication.

Physical Media (Twisted Pair)

A type of cable that consists of two independently insulated wires twisted around one another. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. While twisted-pair cable is used by older telephone networks and is the least expensive type of local-area network (LAN) cable, most networks contain some twisted-pair cabling at some point along the network. Two types of Twisted pair cable available. One is   Shielded   Twisted   Pair   (STP)   and another is Unshielded Twisted Pair (UTP).

Characteristics:

• Inexpensive
• Easy to install and use
• Speed of about 250 Mbps
• Can accommodate about 1,000 devices
• Adequate for network span up to 1/2 Mile

Physical Media (Coaxial Cable)

Type of wire that consists of a center wire surrounded by insulation and then a grounded shield of braided wire. The shield minimizes electrical and radio frequency interference.

Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks. Two types of coaxial cable available

1. 50 Ω (ohm) for Analog Transmission
2. 75 Ω for Digital Transmission

Characteristics:

• Widely available
• Coaxial cable is better than UTP in connecting longer distances (500 meters).
• High data transfer rate (10 Mbps).

Physical Media (Fiber Optic)

Optical fibers carry digital data signals in the form of modulated pulses of light. An optical fiber consists of an extremely thin cylinder of glass, called the core, surrounded by a concentric layer of glass, know as the cladding. There are two fibers per cable- one to transmit and one to receive.

Pulse of light – 1 bit Absence of light – 0 bit

Characteristics:

• Fiber-Optic cable supports up to 1000 stations and can carry signal up to and beyond 50 miles.
• Fiber-Optic cables are also highly secure from outside electrical & noise
• Data Transfer rate in

Nonphysical Media (RF)

Radio Frequency is a special type of radio wave used in wireless communication. Radio Frequency used where hues data transfer is required. Radio Frequency performs communication point to point in a Line of straight (LOS) way. The maximum length of radio frequency is 100 km.

Nonphysical Media (Microwave)

Microwave is a medium type of radio wave used in wireless communication.

Microwave used where point to point communication is required.

Nonphysical Media (Infrared)

Infrared is technique of wireless communication used light source for data interchange. This technique required line of straight for data transmission. This technique used in local area network.