Data Communication: Introduction to Networks and Communication Systems, Essays (university) of Data Communication Systems and Computer Networks

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Chapter # 1:

Introduction

By:

William Stalling

Data Communication

Data Communication

The exchange of data between two devices via

some form of transmission medium such as cable

wire.

For data communications to occur, the

communicating devices must be part of a

communication system made up of combination of

hardware (physical equipments) and software

(programs).

 Delivery

The system must deliver data to the correct destination. Data must be received by the intended device or user and only by that device and user.

 Accuracy

The system must be deliver the data accurately. Data that have been altered in transmission and left uncorrected are unusable.

 Timeline

The system must deliver data in a timely manner. Data delivered late are useless. In case of video and audio, timely delivery means delivering data as they are produced, in the same order that they are produced, and without significant delay. This kind of delivery is

called real time transmission.

 Jitter

Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets. For example, let us assume that video packets are sent every 30-s. If some of the packets arrive with 30- s delay and others with 40-s delay, an uneven quality in the video is the result.

Components

 Message

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

 Sender

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

 Receiver

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

 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 wire and radio waves.

 Protocols

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 Japenese.

Signal Conversion

Data Flow

Half-Duplex

In half-duplex mode, each station can both transmit and receive, and vice versa. The half-duplex mode is like a one-lane road with traffic allowed in both directions.

Full-Duplex

In full-duplex mode(also called duplex), both stations can transmit and receive simultaneously. The full-duplex mode is like a two way street with traffic flowing in both directions share with at the same time.

Network Criteria

A network must be able to meet a certain number of criteria. The most important of these are.

 Performance

 Reliability

 Security

 Performance

Performance can be measured in many ways. Including transit time and response time. 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.

o Transit Time

Transit time is the amount of time required for a message to travel from one device to another.

o Response time

Response time is the elapsed time between an inquiry and a response.

Communications Tasks

Transmission system utilization Addressing

Interfacing Routing

Signal generation Recovery

Synchronization Message formatting

Exchange management Security

Error detection and correction Network management

Transmission System Utilization

 Refers to the need to make efficient

use of transmission facilities that are typically shared among a number of communicating devices. Various techniques (referred to as multiplexing) are used to allocate the total capacity of a transmission medium among a number of users.