Data communications system components

 

A data communications system has five components

1    Message. The message is the information (data) to be communicated. Popular forms of information include text, numbers, pictures, audio, and video.

2    Sender. The sender is the device that sends the data message. It can be a computer, workstation, telephone handset, video camera, and so on.

3    Receiver. The receiver is the device that receives the message. It can be a computer, workstation, telephone handset, television, and so on.

4        Transmission medium. The transmission medium is the physical path by which a message travels from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.

5      Protocol. A protocol is a set of rules that govern data communications. It represents an agreement between the communicating devices. Without a protocol, two devices may be connected but not communicating, just as a person speaking French cannot be understood by a person who speaks only Japanese.

           Data Representation

            Text

            Numbers

             Images

            Audio

            Video

 

    Data Flow-

        Data Flow Communication between two devices can be simplex, half-duplex, or full-duplex as                 shown in Figure. 

            Simplex In simplex mode, the communication is unidirectional, as on a oneway street. Only one             of the two devices on a link can transmit; the other can only receive (Figure a). Keyboards and                 traditional monitors are examples of simplex devices.

 

          Half-Duplex In half-duplex mode, each station can both transmit and receive, but not at the same         time. When one device is sending, the other can only receive, and vice versa (Figure b). Walkie-            talkies and CB (citizens band) radios are both halfduplex systems.

 

        Full-Duplex In full-duplex, both stations can transmit and receive simultaneously (Figure c). One         common example of full-duplex communication is the telephone network. When two people are           communicating by a telephone line, both can talk and listen at the same time. The full-duplex mode         is used when communication in both directions is required all the time.

Network Criteria

A network must be able to meet a certain number of criteria. The most important of these are performance, reliability, and security.

 

Performance; - Performance can be measured in many ways, including transit time and response time. Transit time is the amount of time required for a message to travel from one device to another. Response time is the elapsed time between an inquiry and a response. The performance of a network depends on a number of factors, including the number of users, the type of transmission medium, the capabilities of the connected hardware, and the efficiency of the software. Performance is often evaluated by two networking metrics: throughput and delay. We often need more throughput and less delay. However, these two criteria are often contradictory. If we try to send more data to the network, we may increase throughput but we increase the delay because of traffic congestion in the network.

 

Reliability: In addition to accuracy of delivery, network reliability is measured by the frequency of failure, the time it takes a link to recover from a failure, and the network's robustness in a catastrophe.

 

Security: Network security issues include protecting data from unauthorized access, protecting data from damage and development, and implementing policies and procedures for recovery from breaches and data losses.