Communication means sharing information, it can be local or remote. The term telecommunication means communication at a distance. Data Communication is the exchange of data between devices via some form of transmission medium such as wire cable. The effectiveness of Data Communication system depends on three Fundamental characteristics:
Delivery: The message sent by the source System is correctly delivering to the correct destination is known as Delivery.
Accuracy: The system must deliver the message accurately on the destination System, if any data transmitting from one system to another system gets changed or altered and the same uncorrected bits are received on the destination system results in no use to read the message
Timeliness: The message sent by source system must deliver the data in a timely manner to the destination. Data transmitted and delivered late to the destination systems are useless.
Data Communication deals with the five network components are:
Message: The message is the information or data to be transmitted or communicated form source system to the destination system. This message can be text form, picture form, sound form or any combination of these forms.
Sender: The sender is the device or source system that sends the message. It can be a computer, work station, telephone etc.
Receiver: The receiver is the device or destination system that receives the message from source system or sender device. It can be a computer, workstation, telephone etc.
Medium: A transmission medium is the physical path by which a message travels from sender device to the receiver device or from source system to the destination system.
Protocol: A protocol is set of rules and regulations that govern the data communication. It represents a connection establishment between the source systems and the destination system which will communicate. Without this protocol the connection may not be establish between the source system and destination system or between the sender devices to the receiver device.
In communication represent ting of data can be in text, pictures, images audio and video. The text is represented as bit patterns, a sequence of bits. Different sets of bits patterns have designed to represent by text symbols called as code.
These data representation follow few standards:
ASCII:The American National Standards Institute(ANSI) developed a code called American Standard code for Information Interchange(ASCII).This code uses 7 bits for each symbol to represent it.Extended ASCII: This is similar to the ASCII but takes 1bit more than ASCII code to make size of each pattern 1 byte (8 bits). This Extended ASCII adds zero to the left of the 7 bits to form a pattern of 1 byte ex: 01111111. UNICODE: This Unicode was developed to understand different language as before developed codes understand only English. A coalition of hardware and software design is called Unicode. This is 16 bits and can represent up to 65536 symbols. ISO: This is International Organization for Standardization, designed a code using 32-bit pattern. Numbers & Images also use bit patterns, an image is divided into matrix of pixels
Communication between two devices or systems can differ by the Direction of Data Flow:
Simplex: In Simplex mode, the communication is unidirectional, i.e. only one system can transmit at a time and other system can receive at a time. Key board and monitor are examples of Simplex devices.
Half Duplex: In Half duplex mode, each system can both transmit and receive, but not at the same time. When one device is sending the other can only receive and vice versa. Walkie-Talkies are example for half duplex systems.
Full duplex: In Full duplex mode both systems can transmit and receive simultaneously. The full duplex mode is like a two way street with traffic flowing in both directions at the same time. This sharing of information can be done in two ways:
• Either the link must contain two physically separate transmission path, one for sending and one for receiving.
• The capacity of the channel is divided between signals travelling in both directions.
On a telephone two persons can communicate, both can talk and listen at the same time.