DATA COMMUNICATIONSUNIT-11. What is Data Communication? Ans.Data communication can be defined as Sharing of information,.sharing can be local(face to face) or remote(ove some distance). 2. What are the four fundamental characteristics for effective Data communication ? Ans. The four fundamental characteristics of Data communication are : 1) Delivery :data must be delivered o the correct destination i.e to the intended user. 2) Accuracy : The system must deliver the data accurately(without altering). 3) Timeliness: The data should be delivered within a reasonable time. 4) Jitter: Jitter refers to the variation in the packet arrival time.(deviation from periodicity of video or audio) .

3. What are the components of data communications?Ans. A data communication system has five components1) Message: It is the information(data) to be communicated.2) Sender: The sender is the device that sends the data message.3) Receiver: The receiver is the device that receives the message.4) Transmission medium: It is the physical path by which a message travels from sender to receiver.5) Protocol: A protocol is a set of rules that govern data communications. It is an agreement between communicating devices

4. What are the different forms of Data representations? Ans. Data today comes in different forms such as text, numbers, images, audio, and video.

5. What are the different types of data flow ? Ans. Data flow between two devices can occur in one of three ways: simplex, half-duplex, or full-duplex.

6. What is a simplex mode? Ans. In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive.

7. What is a Half-Duplex mode? Ans. In half-duplex mode, each device can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.

8. What is a Full-Duplex mode?Ans. In full-duplex mode (also called duplex), both devices can transmit and receive simultaneously(at same time).

9. Define Network. Ans. A network is a set of devices (often referred to as nodes) connected by communication Links.

10. What is a link ? Ans. At the lowest level, a network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Link.

11. What is Distributed Processing? Ans. In which a task is divided among multiple computers.

12. What are the criteria necessary for an effective and efficient network?Ans. The most important are performance, reliability and security. Performance: It can be measured in many ways, including transmit time and response time. Reliability: It is measured by frequency of failure, the time it takes a link to recover from a Failure and the network's robustness. Security : Security issues includes protecting data from unauthorized access and viruses.

13. What are the different types of connections ?Ans. There are 2 types of connections1) Point to point: A point-to-point connection provides a dedicated link between two devices2) Multipoint: A multipoint connection is one in which more than two specific devices share a single link.

14. What is a topology? Ans. Topology refers to the physical or logical arrangement of a network. Devices may be arranged in a mesh, star, bus, or ring topology. 15. What is a mesh topology? Ans. In a mesh topology, every device has a dedicated point-to-point link to every other device.

16. What is a Star topology ? Ans. In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub. 17. What is a bus topology? Ans. A bus topology is multipoint. One long cable acts as a backbone to link all the devices in a network

18. What is a ring topology? Ans. In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it.

19. What are the different categories of networkAns. Categories of networks:1) Local Area Network(LAN):it is usually privately owned and links the devices in a single office, building, or campus2) Metropolitan Area Network (MAN): it is a network with a size between a LAN and WAN. It normally covers the area inside a town or a city.3) Wide Area Network(WAN): it provides long-distance transmission of data, image, audio, and video information over large geographic areas that may comprise a country, a continent, or even the whole world.

20. What is protocol ?Ans. A protocol is a set of rules that govern all aspects of information communication.

21. What are the key elements of protocols? Ans. The key elements of protocols area. Syntax :It refers to the structure or format of the data, that is the order in which they are presented. b. Semantics: It refers to the meaning of each section of bits. c. Timing :Timing refers to two characteristics: When data should be sent and how fast they can be sent

22. What is a OSI model ? Ans. It is a Open System Interconnection model. OSI model is to show how to facilitate communication between different systems without requiring changes to the logic of the underlying hardware and software.

23. List the layers of OSI Model Ans. There are 7 layers a. Physical Layer b. Data Link Layer c. Network Layer d. Transport Layer e. Session Layer f. Presentation Layer g. Application Layer

24. What is a peer-to-peer process? Ans. The processes on each machine that communicate at a given layer are called peer-peer process.

25. What are the responsibilities of the Physical Layer? Ans. Physical layer coordinates the functions required to transmit a bit stream over a physical medium.a. Physical characteristics of interfaces and mediab. Representation of bitsc. Data rated. Synchronization of bitse. Line configurationf. Physical topologyg. Transmission mode

26. What are the responsibilities of the Data Link Layer? Ans. The Data Link Layer transforms the physical layer, a raw transmission facility, to a reliable link and is responsible for node-node delivery.a. Framingb. Physical Addressingc. Flow Controld. Error Controle. Access Control

27. What are the responsibilities of Network Layer? Ans. The Network Layer is responsible for the source-to-destination delivery of packet possibly across multiple networks (links). a. Logical Addressingb. Routing

28. What are the responsibilities of Transport Layer? Ans. The Transport Layer is responsible for source-to-destination delivery of the entire message.a. Service-point Addressingb. Segmentation and reassemblyc. Connection Controld. Flow Controle. Error Control

29. What are the responsibilities of Session layer?Ans. The Session layer is the network dialog Controller. It establishes, maintains and synchronizes the interaction between the communicating systems. a. Dialog controlb. Synchronization

30. What are the responsibilities of presentation layer?Ans. The Presentation layer is concerned with the syntax and semantics of the information exchanged between two systems. a. Translation b. Encryption c. Compression

31. What are the responsibilities of Application layer?Ans. The Application Layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as e-mail, shared database management and other types of distributed information services.a. Network virtual Terminalb. File transfer, access and Management (FTAM)c. Mail services d. Directory Services

Essay Questions

1. What is topology? Explain topologies in Data Communications? Ans. The topology refers to the way the network is laid out Physically or logically. The topology of a network is the geometric representation of the relationship of all the links and linking devices (usually called nodes) to one another. There are four basic topologies mesh, star, ring and bus.

Mesh Topology: In a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects.

To find the number of physical links in a fully connected mesh network with n nodes, we first consider that each node must be connected to every other node i.e. every node must be connected to n-1 nodes so we need n(n-1) links. Advantages:a) the use of dedicated links guarantees that each connection can carry its own data load, thus eliminating the traffic problems.b) a mesh topology is robust. If one link becomes unusable, it does not unfit the entire systemc) Privacy or security. When ever message travels along a dedicated line, only the intended recipient sees it

Disadvantagesa) In this we need more cabling and I/O ports.b) Installation and reconnection are difficult .c) As we need more cabling it is expensive.

Star Topology :In a star topology, each device has a dedicated point-to-point link only to a central controller( hub). Unlike a mesh topology, a star topology does not allow direct traffic between devices. The controller acts as an exchange: If one device wants to send data to another, it sends the data to the controller

Advantages a) Less expensive compared to meshb) Robustness If one link fails, only that link is affected. All other links remain active. Disadvantages:a) Dependency on the hub, if the hub goes down entire system fails.

Bus Topology: A bus topology is multipoint. One long cable acts as a backbone to link all the devices in a network. Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable. Advantagesa) Ease of installation.b) It uses less cabling.Disadvantagesa) Difficult in reconnection.b) Fault isolationc) Ring Topplogy: . In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it. Advantagesa) Easy to install and reconfigure.b) Fault isolation is simplifiedDisadvantagesa) Unidirectional traffic

2 .What are the various types of transmission modes and explain.Ans. The transmission mode is used to define the direction of signal flow between 2 linked devices.There are three types of transmission modes simplex, half-duplex and full duplex

Simplex:In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two devices on a link can transmit; the other can only receive.

ReceiverSender

Keyboards and traditional monitors are examples of simplex devices. The keyboard can only introduce input ,the monitor can only accept output.

Half-duplex:In half-duplex mode, each device can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa.

ReceiverSender

Walkie-talkies and CB(citizens band) radios Are both half-duplex systems.

Full-duplex:In full-duplex mode (also called duplex), both devices can transmit and receive simultaneously(at same time).

SenderReceiver

Example of full-duplex communication is the telephone network.