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OSI Model: Industry Standards and Network Theory

This chapter covers the OSI model, industry standards, network theory, and the basics of network communication. Learn about the seven layers of the OSI model, modulation techniques, and the advantages of using a reference model.

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OSI Model: Industry Standards and Network Theory

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  1. Click to edit Master subtitle style Chapter 2: OSI Specifications

  2. Chapter 2 Objectives The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter: • 5.0 Industry standards, practices, and network theory • 5.1 Analyze a scenario and determine the corresponding OSI layer • • Layer 1 – Physical • • Layer 2 – Data link • • Layer 3 – Network • • Layer 4 – Transport • • Layer 5 – Session • • Layer 6 – Presentation • • Layer 7 – Application 2

  3. Chapter 2 Objectives The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter: • 5.2 Explain the basics of network theory and concepts • • Encapsulation/de-encapsulation • • Modulation techniques • o Multiplexing • o De-multiplexing • o Analog and digital techniques • o TDM 3

  4. Internetworking Models • In the late 1970s, the Open Systems Interconnection (OSI) reference model was created by the International Organization for Standardization (ISO) to break through this barrier. • The OSI model was meant to help vendors create interoperable network devices and software in the form of protocols so that different vendor networks could work with each other. • The OSI model is the primary architectural model for networks. It describes how data and network information are communicated from an application on one computer through the network media to an application on another computer. The OSI reference model breaks this approach into layers. 4

  5. Advantages of Reference Models Advantages of using the OSI layered model include, but are not limited to, the following: • It divides the network communication process into smaller and simpler components, thus aiding component development, design, and troubleshooting. • It allows multiple-vendor development through standardization of network components. • It encourages industry standardization by defining what functions occur at each layer of the model. • It allows various types of network hardware and software to communicate. • It prevents changes in one layer from affecting other layers, so it doesn’t hamper development and makes application programming easier. 5

  6. The OSI Model • The OSI model has seven layers: • Application (Layer 7) • Presentation (Layer 6) • Session (Layer 5) • Transport (Layer 4) • Network (Layer 3) • Data Link (Layer 2) • Physical (Layer 1) 6

  7. OSI Layer Functions 7

  8. The Upper Layers 8

  9. The Lower Layers 9

  10. Reliability Reliable data transport employs a connection-oriented communications session between systems, and the protocols involved ensure that the following will be achieved: • The segments delivered are acknowledged back to the sender upon their reception. • Any segments not acknowledged are retransmitted. • Segments are sequenced back into their proper order upon arrival at their destination. • A manageable data flow is maintained in order to avoid congestion, overloading, and data loss. 10

  11. A Connection Oriented Session Sender Receiver SYN SYN/ACK ACK Connection Established Data transfer (Send bytes of Segments) 11

  12. Flow Control Sender Receiver Transmit Buffer full No ready –STOP! Segmentsprocessed GO! Transmit 12

  13. Connection Oriented Session A service is considered connection-oriented if: • Virtual circuit is setup (three-way handshake). • Uses sequencing. • Uses acknowledgments. • Uses flow control. 13

  14. Windowing Flow Control Sender Receiver Window size of 1 Send 1 Receive 1 Ack 1 Receive 2 Send 2 Ack 2 Window size of 3 Send 1 Send 2 Send 3 Ack 4 Send 4 14

  15. Acknowledgements Sender Receiver Send 1 Send 2 Send 3 Ack 4 Send 4 Send 5 Connection lost! Send 6 Ack 5 Send 5 Ack 7 15

  16. The Lower Layers 16

  17. Routing at Layer 3 3.0 1.0 3.1 1.1 2.1 2.2 3.3 1.3 E0 E0 S0 S0 3.2 1.2 17

  18. Routers at Layer 3 Internet FastEthernet0/0 Serial0 WAN Services FastEthernet0/1 Each router interface is a broadcast domain.Routers break up broadcast domains bydefault and provide WAN services 18

  19. The Lower Layers 19

  20. Data Link Layer (Layer 2) 802.11 802.3 802.2 20

  21. The Lower Layers 21

  22. Data Encapsulation PDU Application Presentation Upper layer data Session TCP Header Upper layer data Transport Segment Network Segment IP Header Packet Packet FCS LLC Header Data Link Frame Packet MAC Header FCS 0101110101001000010 Physical Bits 22

  23. Modulation Techniques Modulation is the process of varying one or more properties of a waveform called a carrier signal In current networks, modulation takes digital or analog signals and puts in in another signal that can be physically transmitted Modems – perform both modulation and demodulation operations Analog and Digital modulation use Frequency-Division multiplexing. Several low-pass signals transferred simultaneously over same shared medium Ethernet uses digital baseband modulation or line coding to transfer digital bit stream Time-division multiplexing (TDM) method of transmitting and receiving many independent signals over common signal path through synchronize devices 23

  24. Summary • Summary • Exam Essentials Section • Written Labs • Review Questions 24

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