Data Communication and Networking

1. Data Communication and Networking For more such slides visit bcc2000.com

2. Data Communication • Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable. Or Data Communication technologies deal with means and methods of data transfer from one location to another. • Basic Elements of Communication System • A SENDER(source) that creates and sends a message. • A MEDIUM that carries the message. • A RECEIVER that receives the message.

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4. Data Transmission Modes • Simplex, half-Duplex and Full- Duplex

5. Various Transmission Media • Twisted-Pair Wire • Coaxial Cable • Microwave System • Communication Satellite • Optical Fibers Bajaj Coaching Center, Rohtak

6. Digital and Analog Data Transmission • Data is transmitted from one point to another point by means of electrical signals that may be in digital and analog form. • In Analog signal the transmission power varies over a continuous range with respect to sound, light and radio waves.  • A Digital signal may assume only discrete set of values within a given range.

7. Analog signal is measured in Volts and its frequency in Hertz (Hz). A digital signal is a sequence of voltage represented in binary form. • When digital data are to be sent over an analog form the digital signal must be converted to analog form. So the technique by which a digital signal is converted to analog form is known as modulation. And the reverse process, that is the conversion of analog signal to its digital form, is known as demodulation. • The device, which converts digital signal into analog, and the reverse, is known as modem.

8. Analog Signal Digital signal

9. Switching Techniques • In large networks there might be multiple paths linking sender and receiver. Information may be switched as it travels through various communication channels. There are three typical switching techniques available for digital traffic. • Circuit Switching • Message Switching • Packet Switching Bajaj Coaching Center, Rohtak

10. Circuit Switching • Circuit switching is a technique that directly connects the sender and the receiver in an unbroken path. • Telephone switching equipment, for example, establishes a path that connects the caller's telephone to the receiver's telephone by making a physical connection. • With this type of switching technique, once a connection is established, a dedicated path exists between both ends until the connection is terminated. Bajaj Coaching Center, Rohtak

11. Circuit switching • Advantages: • The communication channel (once established) is dedicated. • Disadvantages: • Possible long wait to establish a connection, (10 seconds, • more on long- distance or international calls.) during which • no data can be transmitted. • More expensive than any other switching techniques, • because a dedicated path is required for each connection. • Inefficient use of the communication channel, because the • channel is not used when the connected systems are not • using it.

12. Message Switching • With message switching there is no need to establish a dedicated path between two stations. • When a station sends a message, the destination address is appended to the message. • The message is then transmitted through the network, in its entirety, from node to node. • Each node receives the entire message, stores it in its entirety on disk, and then transmits the message to the next node. • This type of network is called a store-and-forward network.

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14. Message Switching • Advantages: • Channel efficiency can be greater compared to circuit- • switched systems, because more devices are sharing the channel. • Traffic congestion can be reduced, because messages may be temporarily stored in route. • Message priorities can be established due to store-and-forward technique.

15. Message Switching • Disadvantages • Message switching is not compatible with interactive • applications. • Store-and-forward devices are expensive, because they • must have large disks to hold potentially long messages.

16. Packet Switching • In packet switching methods, a message is broken into • small parts, called packets. • Each packet is tagged with appropriate source and destination • addresses. • Since packets have a strictly defined maximum length, they • can be stored in main memory instead of disk, therefore access delay and cost are minimized. • With current technology, packets are generally accepted onto • the network on a first-come, first-served basis. If the network • becomes overloaded, packets are delayed or discarded • (``dropped''). Bajaj Coaching Center, Rohtak

17. Packet Switching • Advantages: • Packet switching is cost effective, because switching • devices do not need massive amount of secondary • storage. • Packet switching offers improved delay characteristics, • because there are no long messages in the queue • (maximum packet size is fixed). • Packet can be rerouted if there is any problem, such as, • busy or disabled links. • The advantage of packet switching is that many • network users can share the same channel at the same • time.

18. Disadvantages of packet switching • It can add some initial costs in implementation. • If packet is lost, sender needs to retransmit the data. • There is no guarantee of how long it takes to travel from its source node to its destination node, because time taken for each packet depends on route chosen for that packet. Bajaj Coaching Center, Rohtak

19. Communication Protocols • How do the computers send and receive data across communication links? The answer is data communication software. • It is this software that enables us to communicate with other systems. The data communication software instructs computer systems and devices as to how exactly data is to be transferred from one place to another. The procedure of data transformation in the form of software is commonly called protocol. Bajaj Coaching Center, Rohtak

20. The data transmission software or protocols perform the following functions- Data sequencing: A long message to be transmitted is broken into smaller packets of fixed size for error free data transmission. Data Routing: It is the process of finding the most efficient route between source and destination before sending the data. Flow control: All machines are not equally efficient in terms of speed. Hence the flow control regulates the process of sending data between fast sender and slow receiver. Error Control: It ensures that data are transmitted without any error.

21. What is a Network? • A network consists of 2 or more computers connected together, and they can communicate and share resources (e.g. information). Bajaj Coaching Center, Rohtak

22. Why Networking? • Sharing information — i.e. data communication • Sharing hardware or software • E.g. print document • Centralize administration and support • E.g. Internet-based, so everyone can access the same administrative or support application from their PCs Bajaj Coaching Center, Rohtak

23. The Disadvantages (Costs) of Networking • Network Hardware, Software and Setup Costs • Hardware and Software Management and Administration Costs • Undesirable Sharing • Illegal or Undesirable Behavior • Data Security Concerns

24. Fundamental NetworkClassifications • LAN- Networks used to interconnect computers in a single room, rooms within a building or buildings on one site are called Local Area Network (LAN). LAN transmits data with a speed of several megabits per second (106 bits per second). The transmission medium is normally coaxial cables. • LAN links computers, i.e., software and hardware, in the same area for the purpose of sharing information. Usually LAN links computers within a limited geographical area because they must be connected by a cable, which is quite expensive. Bajaj Coaching Center, Rohtak

25. Major Characteristics of LAN • Every computer has the potential to communicate with any other computers of the network. • High degree of interconnection between computers. • Easy physical connection of computers in a network. • Inexpensive medium of data transmission. • High data transmission rate.

26. Advantages • The reliability of network is high because the failure of one computer in the network does not effect the functioning for other computers. • Addition of new computer to network is easy. • High rate of data transmission is possible. • Disadvantages • If the communication line fails, the entire network system breaks down. Bajaj Coaching Center, Rohtak

27. Metropolitan Area Network (MAN): • A metropolitan area network (MAN) is a network that interconnects users with computer resources in a geographic area or region larger than that covered by even a large local area network (LAN) but smaller than the area covered by a wide area network (WAN). The term is applied to the interconnection of networks in a city into a single larger network (which may then also offer efficient connection to a wide area network). Bajaj Coaching Center, Rohtak

28. Wide Area Networks (WANs): • The term Wide Area Network (WAN) is used to describe a computer network spanning a regional, national or global area. For example, for a large company the head quarters might be at Delhi and regional branches at Bombay, Madras, Bangalore and Calcutta. Here regional centers are connected to head quarters through WAN. The distance between computers connected to WAN is larger. Therefore the transmission medium used are normally telephone lines, microwaves and satellite links. • The largest and most well-known example of a WAN is the Internet

29. Characteristics of WAN • Communication Facility: For a big company spanning over different parts of the country the employees can save long distance phone calls and it overcomes the time lag in overseas communications. Computer conferencing is another use of WAN where users communicate with each other through their computer system. • Remote Data Entry: Remote data entry is possible in WAN. It means sitting at any location you can enter data, update data and query other information of any computer attached to the WAN but located in other cities. For example, suppose you are sitting at Madras and want to see some data of a computer located at Delhi, you can do it through WAN. Bajaj Coaching Center, Rohtak

30. Characteristics of WAN Cont… • Centralised Information: In modern computerised environment you will find that big organisations go for centralised data storage. This means if the organisation is spread over many cities, they keep their important business data in a single place. As the data are generated at different sites, WAN permits collection of this data from different sites and save at a single site.

31. NETWORK TOPOLOGY • The term topology in the context of communication network refers to the way the computers or workstations in the network are linked together. According to the physical arrangements of workstations and nature of work, there are four major types of network topology. • Star • Ring • Bus • Hybrid

32. Star topology • In star topology a number of workstations (or nodes) are directly linked to a central node Any communication between stations on a star LAN must pass through the central node.

33. Advantages of Star Topology • It offers flexibility of adding or deleting of workstations from the network. • Breakdown of one station does not affect any other device on the network. • Disadvantage • Failure of the central node disables communication throughout the whole network.

34. Ring Topology • In ring topology each station is attached nearby stations on a point to point basis so that the entire system is in the form of a ring. In this topology data is transmitted in one direction only. Thus the data packets circulate along the ring in either clockwise or anti-clockwise direction.

35. Advantages Of Ring Network • Ring Network works Well where there is no central node for making routing decisions. • It is more reliable than a star network because communication is not dependent on a single central node. If a link between any two nodes fails, or if one of the nodes fails, alternate routing is possible.

36. Disadvantage • The ring makes it difficult to add new computers. • The disadvantage of ring network is that the breakdown of any one station on the ring can disable the entire system.

37. Bus Topology • In bus topology all workstations are connected to a single communication line called bus. In this type of network topology there is no central node as in star topology. Transmission from any station travels the length of the bus in both directions and can be received by all workstations.

38. Advantages • It is quite easy to set up. • If one station of the topology fails it does not affect the entire system. • Addition of new nodes to the network is easy. • Disadvantage • The disadvantage of bus topology is that any break in the bus is difficult to identify. Bajaj Coaching Center, Rohtak

39. Hybrid Network • It is a combination of two or more different network topologies.

40. Mesh Topology • Mesh topology is where all nodes are connected directly to all other nodes. If N is the number of nodes, then N(N-1)/2 links are required to provide a full mesh.  Bajaj Coaching Center, Rohtak