Data Communications Physical Layer of OSI

Introduction: Data Communications, Networks, Network Types, Networks Models: Protocol
Layering, TCP/IP Protocol suite, The OSI model, Introduction to Physical Layer: Transmission
media, Guided Media, Unguided Media: Wireless. Switching: Packet Switching and its types.

1. Presented By Mr. B.Sashi Kanth Assistant Professor Department of ECE COMPUTER NETWORKS Vignan’s Institute of Engineering for Women Affiliated to JNTUK Visakhapatnam, Andhra Pradesh.

2. Overview about Units in Computer Networks 2

3. 3 UNIT-I Introduction to Computer Networks Basics of Computer Networks Network Criteria Issues Network Topologies OSI Reference Model TCP/IP Model Bandwidth limited signals Guided Transmission Media Digital modulation FDM, TDM CDM Data link layer design Issues Error Detection and Correction Data link Protocols Sliding Window Protocol UNIT-II Physical Layer & Data Link Layer

4. 4 UNIT-III Services provided to network layer Framing Error Correcting and detecting codes Simplex stop and wait protocol Simplex stop and wait protocol with noisy channel One-bit sliding window protocol UNIT-IV Medium Access Control Sub-Layer Static Channel Allocation Dynamic Channel Allocation ALOHA Wireless LAN Protocols MAC Sub layer Protocols Ethernet Performance 802.11 Architecture and Protocol 805.11 Frame Structure

5. 5 UNIT-V Network Design Issues Store and forward packet switching Transport layer connectionless and connection-oriented Routing algorithms Congestion Control algorithm Traffic throttling & Load shedding UNIT-VI Internet Transport Protocols & Application Layer UDP TCP DNS Resource Records E-Mail Architecture and Services Message Format and transfer Final Delivery of E-Mail

6. 6

7. CONTENTS Definition of Computer Networks Data Communication system &Components of Comm. system Data Respresentation Data Flow in different ways. Network Criteria. Type of Connections. Topology and Different types of Topology. Categories of Networks. Internet Service Providers OSI Reference Model TCP/IP Model 7

8. What is Computer Networks? A computer network is a set of devices connected through links. A node can be computer, printer, or any other device capable of sending or receiving the data. The links connecting the nodes are known as communication channels . Fig 1: Computer Network Connection 8

9. Data Communication System What is Data Communication system? Fig 2: Data Communication System Components of Data Communication Message Sender Receiver Transmission Media Protocol 9

10. Data Representation can be different ways i.e. Text, numbers, images, audio and video format. Dataflow representation can be different ways. Simplex Half-Duplex Full Duplex Fig 3: Dataflow communication system 10

11. What is Network? A network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network . Network Criteria is able to meet some issues like… Table 1: Network Criteria Issues 11 Performance Transit time & Response time Reliability Accuracy of delivery & Recovery of link Failures. Security Protecting data from Unauthorized access and implementing policies & Procedures.

12. Types of Connections A network is two or more devices connected through links. A link is a communications pathway that transfers data from one device to another. Point to Point Connection. Multi-point Connection. Fig 4: Types of Connections 12

13. What is Topology? Topology means the manner in which nodes are geometrically arranged and connected is known as the Topology of the network. (or) Two or more devices connect to a link; two or more links form a topology . Topology are two types:- 1. Physical Topology 2 . Logical Topology. Physical Topology : It refers to network interconnection in physical manner actually in wire or transmission media. Logical Topology : It defines how the host access media to send data. 13

14. Logical Topology Fig 5: Logical Topology Connections 14

15. Bus Topology Bus Topology also called horizontal topology. A networking topology that connects networking components along a single cable or that uses a series of cable segments that are connected linearly. A network that uses a bus topology is referred to as a “bus network .” Fig 6: Bus Topology 15

16. Advantages Easy to use and easy to install . Costs are usually low Easy to add systems to network Great for small networks . A repeater can also be used to extend a bus topology network. Disadvantages Heavy network traffic can slow a bus considerably . Failure a cable affects all devices on the network . It is difficult to troubleshoot a bus . Unmanageable in a large network If cable breaks, whole network is down 16

17. Ring Topology In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it. A signal is passed along the ring in one direction, from device to device, until it reaches its destination . Fig 7: Ring Topology Each device in the ring incorporates a repeater. 17

18. Advantages: Easy to install . Easy to reconfigure .   Fault identification is easy .   Disadvantage : Unidirectional traffic .   Break in a single ring can break entire network .   Adding or removing nodes disrupts the network .   It is difficult to troubleshoot a ring network .   Much slower than an Ethernet network under normal load .   Cost of cable is more in ring network. 18

19. 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 connect n nodes in Mesh topology, we require n(n-1)/2 duplex mode links. Fig 8: Mesh Topology 19

20. Advantages : Troubleshooting is easy . Robust, If one link becomes unusable, it does not incapacitate the entire system . Advantage of privacy or security . fault identification and fault isolation easy , Traffic can be routed to avoid links with suspected problems .   Disadvantage : Required high amount of cabling and the number of I/O ports . Costly because of maintaining redundant links . Difficulty of reconfiguration. 20

21. Problem for Mesh Topology 1. A mesh network has 8 devices. Calculate total number of cable links and IO ports needed . Solution : Number of devices = 8   Number of links = n (n-1)/ 2 8(8-1)/2 = 28   Number of port/device = n-1 = 8-1 = 7 21

22. Star Topology In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub . The devices are not directly linked to one another . The controller acts as an exchange: If one device wants to send data to another, it sends the data to the controller, which then relays the data to the other connected device . Fig 9 : Star Topology 22

23. Advantages :   Less Expensive than mesh topology . Installation and configuration are easy . Less cabling is need then mesh . Robustness . Easy to fault identification & isolation . Disadvantage : If the central hub fails, the whole network fails to operate. Each device requires its own cable segment . Installation can be moderately difficult. 23

24. Hybrid Topology It is two different types of topologies which is a mixture of two or more topologies. For example if in an office in one department ring topology is used and in another star topology is used, connecting these topologies will result in Hybrid Topology (ring topology and star topology ). Fig 10: Hybrid Topology 24

25. Advantages Reliable as Error detecting and trouble shooting is easy . Effective . Scalable as size can be increased easily . Flexible . Disadvantage Complex in design . Costly. 25

26. Categories of Networks 1. Local Area Network (LAN) 2. Metropolitan Area Network (MAN) 3. Wide Area Network (WAN) 26

27. Local Area Network (LAN) Local area networks, generally called LANs, are privately-owned networks within a single building or campus of up to a few kilometres in size . They are widely used to connect personal computers and workstations in company offices and factories to share resources (e.g., printers) and exchange information . Traditional LANs run at speeds of 10 Mbps to 100 Mbps, have low delay (microseconds or nanoseconds), and make very few errors . Fig 11: LAN Connection through Hub 27

28. MAN (Metropolitan Area Network) MAN is a network that spans a city. The network consists of various buildings interconnected Via either wireless or fiber optics backbones . A metropolitan area network(MAN) is a large computer network that usually spans a city or a large campus. The best-known example of a MAN is the cable television network available in many cities . MAN provides the transfer rates from 34 to 150 Mbps. Fig 12: Metropolitan Area Network 28

29. WAN (Wide Area Network) A network that spans broader geographical area than a local area network over public communication network. WANs interconnect LANs, which then provide access to computers or file servers in other locations . WANs provide instant communications across large geographic areas. Fig 13: Relation between hosts on LAN and subnet 29

30. Internet Service Providers (ISPs) 1. International Internet Service Providers. 2. National Internet Service Providers 3. Regional Internet Service Providers Fig 14: Internet Service Providers (ISPs) 30

31. Protocols and Standards A protocol is a set of rules that govern data communications. A protocol defines what is communicated, how it is communicated, and when it is communicated. The key elements of a protocol are syntax, semantics, and timing. Syntax. Semantics. Timing. 31

32. LAYERED TASKS 32 Fig 15: Layered Task

33. Layers can offer two different types of service to the layers: connection-oriented and connectionless. Fig 16: Five service primitives for implementing a simple connection-oriented service. 33

34. OSI REFERENCE MODEL This model is based on a proposal developed by the International Standards Organization (ISO) as a first step toward international standardization of the protocols used in the various layers . The model is called the ISO-OSI (Open Systems Interconnection ). 34

35. OSI Reference Model Seven layers 35

36. Inter Connection between layers 36

37. The interaction between layers in the OSI model 37

38. OSI MODEL EXCHANGE DATA 38

39. Physical Layer Physical layer is the bottom layer of the OSI reference model.   The physical layer is concerned with transmitting raw bits over a communication channel. The design issues have to do with making sure that when one side sends a 1 bit, it is received by the other side as a 1 bit, not as a 0 bit. 39

40. Physical Layer To transmit the stream of bits they must be encoded into signal . The sender and receiver not only must use the same bit rate but also must be synchronized at the bit level . In the physical layer the devices can be connected to point- to-point connection or multi-point connection The physical layer data transmission can be any different ways i.e. simplex, half-duplex and full-duplex. 40

41. Data-Link Layer Data Link Layer is divided into two sub-ways i.e. The LLC layer is responsible for flow control, error correction and resequencing of information in connection-oriented and connectionless services. The MAC Layer is responsible for providing gain access to the medium. 41

42. Data-Link Layer The data link layer divides the stream of bits received from the network layer into manageable data units called frames . the data link layer adds a header to the frame to define the sender and/or receiver of the frame . 42

43. Data-Link Layer Flow Control: If the rate at which the data are absorbed by the receiver is less than the rate at which data are produced in the sender, the data link layer imposes a flow control mechanism to avoid overwhelming the receiver . Error Control: To improve the reliability the Datalink layer adds a trailer which contains the error control mechanism like CRC, Checksum etc . Access control: When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time. 43

44. Network Layer Network Layer key design issue how to route packets format (Data) from source to destination. Network layer is responsible for functions of: Logical addressing and routing of packets over the network . Establishing and releasing connections and paths between two nodes on a network. Transferring data , generating and confirming receipts , and resetting connections . 44

45. Network Layer Logical addressing : Data link layer implements physical addressing. When a packet passes network boundary, an addressing system is needed to distinguish source and destination, network layer performs these functions. The network layer adds a header to the packet of upper layer includes the logical addresses of sender and receiver . The network layer also supplies connectionless and connection-oriented services to the transport layer above it. 45

46. Transport layer The transport layer is responsible for providing reliable transport services to the upper-layer protocols. Flow control to ensure that the transmitting device does not send more data than the receiving device can handle. 46

47. Transport Layer Segmentation and reassembly . A message is divided into manageable units called as segments .   Each segment is reassembled after received that information at the receiver end .   To make this efficient each segment contains a sequence number .   Error handling and acknowledgments to ensure that data is retransmitted when required . Multiplexing for combining data from several sources for transmission over one data path. 47

48. Session Layer The session layer allows users which enables sessions between computers on a network to be established and terminated . 48

49. Session Layer Dialog control: The session layer allows two systems to enter into a dialog. It allows the communication between two processes to take place in either half- duplex (one way at a time) or full-duplex (two ways at a time) mode. Token management : preventing two parties from attempting the same critical operation at the same time. Synchronization : The session layer allows a process to add checkpoints, or synchronization points, to a stream of data. Check pointing long transmissions to allow them to continue from where they were after a crash. 49

50. Presentation Layer The presentation layer is concerned with the syntax and semantics of the information exchanged between two systems . Specific responsibilities of layer: Translation Encryption Compression 50

51. Application Layer The application layer contains a variety of protocols that are commonly needed by users. One widely-used application protocol is HTTP (Hypertext Transfer Protocol), which is the basis for the World Wide Web. 51

52. Application Layer Network Virtual Terminal: It is a software version of a physical terminal and allows a user to log on to a remote host . File Transfer, Access, and Management : It allows a user to access files in a remote computer, retrieve files, and manage or control files in a remote computer . Mail Services: It provides the basis for e-mail forwarding and storage . Directory Services: It provides distributed database sources and access for global information about various objects and services 52

53. TCP/IP Reference Model Host-to-Network Layer Internet Layer Transport Layer Application Layer 53

54. HOST-TO-NETWORK LAYER : At the physical and data link layers, TCPIIP does not define any specific protocol. It supports all the standard and proprietary protocols. A network in a TCPIIP internetwork can be a local-area network or a wide-area network . INTERNET LAYER : At the network layer (or, more accurately, the internetwork layer), TCP/IP supports the Internetworking Protocol. IP, in turn, uses four supporting protocols: ARP,RARP, ICMP, and IGMP . Internetworking Protocol (IP): The Internetworking Protocol (IP) is the transmission mechanism used by the TCP/IP protocols. It is an unreliable and connectionless protocol-a best-effort delivery service. 54

55. TCP/IP Protocol Address Resolution Protocol: The (ARP) is used to determine the physical address when logical address is known . Reverse Address Resolution Protocol: The (RARP) is used to determine the logical address when physical address is known . Internet Control Message Protocol: The (ICMP) is a protocol that is used to control the flow of message over transmission medium by sending notification messages to the sender . Internet Group Message Protocol: The(IGMP) is used to facilitate the simultaneous transmission of a message to a group of recipients. 55

56. TCP is a reliable stream transport protocol. The term stream, in this context, means connection-oriented. User Datagram Protocol : UDP is the simpler of the two standard TCP/IP transport protocols. It is a process-to-process protocol that adds only port addresses, checksum error control, and length information to the data from the upper layer . Stream Control Transmission Protocol : The SCTP provides support for newer applications such as voice over the Internet. It is a transport layer protocol that combines the best features of UDP and TCP. 56

57. THE APPLICATION LAYER : The TCP/IP model does not have session or presentation layers. On top of the transport layer is the application layer.   It contains all the higher-level protocols. The early ones included virtual terminal (TELNET), file transfer (FTP), and electronic mail (SMTP) The virtual terminal protocol allows a user on one machine to log onto a distant machine and work there. The file transfer protocol provides a way to move data efficiently from one machine to another. Electronic mail was originally just a kind of file transfer, but later a specialized protocol (SMTP) was developed for it .   Many other protocols have been added to these over the years: the Domain Name System (DNS ) 57

58. Conclusion Definition of Computer Networks is known. Data Communication system &Components of Comm. system Data Respresentation Data Flow in different ways is known. Network Criteria is known. Type of Connections is explained. Topology and Different types of Topology is seen. Categories of Networks is explained. Internet Service Providers OSI Reference Model with diagrams is explained TCP/IP Model is explained. 58

59. Assignment Questions What is layered architecture? Explain its design issue ? Describe the network types, topologies and switching methods . Compare the OSI and TCP/IP reference model . Explain OSI reference model, with neat sketch. 59

60. FAQs – Short Answers What is the significance of layered architecture ? What is point-to-point link transmission ? What are the responsibilities of physical layer ? Explain in detail about the MAN . What is the difference between LAN and WAN? List and explain the five components of a data communication system. 60

61. FAQs – Long Answers What is layered architecture? Explain its design issue? Describe the network types. Compare the OSI and TCP/IP reference model. Explain OSI reference model, with neat sketch . Explain about TCP/IP Model. Explain different topologies models. 61

62. Interactions 62

63. B.Sashi Kanth Assistant Professor Department of Electronics and Communication Engineering Vignan’s Institute of Engineering for Women Affiliated to JNTUK Visakhapatnam, Andhra Pradesh. Email ID: [email protected] THANK YOU 63