Data Communication

Data Communication Waqas Ali Sahito Lecturer Department of Computer Science

Data Communication • “Data Communication is the exchangeof Informationfrom one entityto the other using a TransmissionMedium”. • As you can clearly notice, the definition of Data Communication although Simple leaves many questions unanswered: • ¾ Exchange?????? • ¾ Information????? • ¾ Entities??????? • ¾ Transmission???? • ¾ Medium????

Cont… • Or we Can Say • When we communicate, we are sharing information, this sharing can be local or remote, between individuals, local communication normally occurs face to face, while remote communication takes place over distance , the work “tele-communication ” is best example of communication over distance

Cont… • Data Communication are the exchange of data between two devices via some form of transmission medium, such as wireless or cable, for data communication to occur, communication devices must be part of communication system made up of combination of hardware and software,

Characteristics of Data Communication • The effectiveness of Data Communication depends on these fundamental characteristics. • Delivery • Accuracy • Timeliness • Jitter

Characteristics of Data Communication Delivery: The system must deliver the data to correct destination, data must be received by intended device or the user and only by that device or user. Accuracy: The System must deliver the data accurately, Data altered in transmission and left uncorrected are unusable

Characteristics of Data Communication • Timeliness: The system must deliver data in timely manner, data delivered late are useless. Incase of video and audio timely delivery means data must be delivered as it is produced, in the same order they are produced and without significant delay. This type of delivery is called “Real Time Transmission”.

Characteristics of Data Communication • Jitter: It refers to the variation in the packet arrival time, It is the uneven delay in the video or audio packets, • For example: Video packets are sent every 30 ms, if some packets arrive at 30 ms delay and some packets arrive at 40 ms delay than uneven quality in the video will be the result.

Few key words • Packet: A technology for breaking digital data up into small units (packets) for data transmission. • Transmission: Sending and receiving the data is called transmission. • Data: Information presented in whatever form is agreed upon by the both parties ( sender and receiver) is called data.

Components of Data Communication • Data Communication has Five components.

Components of Data Communication • Message • Sender • Receiver • Transmission medium • Protocol

Components of Data Communication • Message: • Information or Data to be communicated, It can be text, numbers, video or any combination of these. In short anything that can be represented using binary bits

Components of Data Communication • Data Communication Messages • Files(meaningful collections of records) • Data/information requests(database queries, Web page requests, etc.) • Responsesto requests and commands or error messages • Status messages(about the network’s functional status) • Control messagestransmitted between network devices to control network traffic • Correspondenceamong network users

Components of Data Communication • SENDER: Device that sends the data message, Can be a Computer , Workstation, Video camera etc, As already discussed, the data from the sender might not be in the appropriate format for the transmission medium and will need to be processed

Components of Data Communication • RECEIVER Device that receives the message, Can be a computer, workstation, Television etc At times, the data received from the transmission medium may not be in a proper form to be supplied to the receiver and it must be processed

Components of Data Communication • Transmission medium • Physical path that a message uses to travel from the Sender to the receiver , Can be a Copper Cable (Telephone), Coaxial Cable (Cable TV), Fiber Optic Cable, LASERS or Radio Waves (Wireless Medium). We will see that Data needs to be transferred in the form of ELECTROMAGNETIC signals and The Transmission Medium should be capable of carrying these EM Signals Transmission Media

Components of Data Communication • PROTOCOL Set of Rules Governing Communication Represents an Agreement between communication devices. Without Protocol, two devices may be connected but they will not be able to communicate • For-example: Consider the communication between two individuals. They can only communicate provided they both speak the same language.

Data Flow

Simplex • In simplex mode the communication is uni-directional as one way road, only one of the two devices on the link can transmit, keyboards and traditional monitors are the examples of simplex devices, the keyboard can only introduce input while the monitor can only accept output, It can take entire capacity to send the data in one direction

Simplex

Half Duplex • In half duplex each station can send and receive the data but one at a time, when one device is sending the other device can only receive, the half duplex transmission takes full capacity of the line for whichever device is sending the data, “ Walkie Talkie is the best example of half duplex.

Half-Duplex

Duplex / Full Duplex • In full duplex mode ( also called duplex) both the devices can send and receive the data at the same time, In full duplex the signal going in the one direction share the capacity of the line with signals going in the other direction. • The sharing may occur in two ways, • Either the link may contain two separate physical transmission paths, one for sending and one for receiving.

Cont.. • Or the capacity of the line is divided into the signals travelling in both directions. • One common example of the full duplex communication is “ Tele-phone “

Full-Duplex

Network • A network is set of devices ( often referred as nodes) connected by a communication link. A node can be a computer, printer or any other device that can be capable of sending and receiving data generated by other node on the network.

Distributed Processing • Most of networks use distributed processing, in which a task is divided into multiple computers, Instead of one single large machine being responsible for all aspects of the process, separate computers ( usually PCs or workstations) handle a subset.

Net Work Criteria • A network must meet certain number of criteria, The most important are, • Performance • Reliability • Security

Network Criteria • Performance Performance can be measured in many ways, including transit time and response time, where transit time is amount of time required for a message to travel from one device to an other, and response time is the elapsed time between an inquiry and response.

Cont… • The performance of the network depends on number of factors, including the number of users, the type of transmission medium, the capability of connected hardware and efficiency of the software, Performance is often measured in two metrics: Throughput and Delay.

Cont… • We often need more throughput and less delay, however these two metrics are contradictory, If we try to send more data on the network, we may increase the throughput but we increase the delay as well because of congestion in the network

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

Cont.. • Security • Network security issue includes protecting data from un authorized access, protecting data from damage and development, and implementing policies and procedures from breaches and data losses.

Thank You

Figure 2-15 The McGraw-Hill Companies, Inc., 1998 WCB/McGraw-Hill

Figure 2-16 Local Area Network The McGraw-Hill Companies, Inc., 1998 WCB/McGraw-Hill

Data Communication