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CCNA1 – Chapter 2

CCNA1 – Chapter 2. OSI - model. Objectives. General model of communication. The OSI reference model. Comparison between OSI and TCP/IP reference model. Overview. In the early 1980s, companies began to implement their. proprietary. (private) network.

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CCNA1 – Chapter 2

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  1. CCNA1 – Chapter 2 OSI - model

  2. Objectives • General model of communication • The OSI reference model • Comparison between OSI and TCP/IP reference model

  3. Overview • In the early 1980s, companies began to implement their proprietary (private) network. • Every company developed its own networking devices & software. • So , each network implemented its own specifications.

  4. incompatible • The result was networks (because of the absence of Standards. • Subsequently, the communication between networks was very difficult. • There was a need to develop networking standards to ensure the Interoperability between Networks.

  5. ISO created OSI model in 1984. In this chapter we will study: • The importance of OSI model • the basic functions of each OSI layer. • Data flow over networks.

  6. Example of layering model Has his own responsibilities (functions) Director general Has her own responsibilities (functions) secretary Provides fax services (functions) Fax • Each layer performs a group of functions (layer N) .

  7. Has his own responsibilities (functions) Director general (layer N) Has her own responsibilities (functions) (layer N-1) secretary Provides fax services (functions) Fax (layer N-2) • Each layer provides services to the layer above it.

  8. English director general is going to send a fax to French director general. Director general (French) Director general (English) (layer N) layer N layer N-1 Secretary (English/ French) Secretary (English/ French) (layer N-1) layer N-2 Fax (layer N-2) Fax

  9. Passes the text (with instructions) Sent the fax Director general (French) Director general (English) (layer N) Writes the text Peer-to-peer Translated text Secretary (English/ French) Secretary (English/ French) Translates the text (layer N-1) Peer-to-peer Secretary picks up the text Fax (layer N-2) Fax Physical communication

  10. Director general (French) Director general (English) (layer N) Secretary (English/ French) Secretary (English/ French) (layer N-1) Fax (layer N-2) Fax • Change of one layer (director general, secretary or fax) will not require a change of any other layer.

  11. OSI reference model

  12. Networking concepts . . . • Networking is the interconnection of workstations, peripherals and other devices. • All devices must speak the same language Protocol: is the rules that governs the data format and data exchange.

  13. Layer N in one computer communicates with layer N on another computer. Peer –to –peer communication Using layer N protocol

  14. Source , destination, and data packets: • Data is sent in bits, 1s, and 0s. • Data stream is broken into smaller units, called Packets. Why ? • every computer can take its turn in transmitting data. • If packet is lost, only a small amount of data is retransmitted.

  15. Packets can take different paths. • Each packet must include the identity of the sending device Source address and the identity of the receiving device Destination address

  16. Different Media Types AIR carries light, radio, microwave Media—material through which data packets travel

  17. Why a layered Network model? • It divides a network communication process into smaller parts: • Easier to develop network components. • Easier to design networks. • Easy to troubleshoot network problems. • Easier to manage networks.

  18. It standarizes network devices and software: • Ensures compatibility (interoperability) between devices from different vendors. • It prevents changes in one layer from affecting the other layers: • Layers are developed quickly. • Accelerates the evolution of networks. • Simplifies the learning process.

  19. The seven layers of OSI model • Data flow is divided into seven smaller and manageable steps. • What devices operate at each layer. • As a result, you will understand how to trouble shoot network problems.

  20. Functions of each layer

  21. The application layer: • Provides services to user’s applications. • Ensures the availability of intended communication partner. • Ensures the existence of sufficient network resources (ex. NIC). • Synchronizes and establishes agreement on error recovery. • Data integrity.

  22. The application layer: • services to user’s applications. • Data format. • Insures data is readable by the receiving system. • Translates between different data formats. • Compression /decompression • Encryption/ decryption.

  23. The session layer: • services to user’s applications. • Data format. • Establishes, manages and terminates commun. between presentation layer entities. • Dialog management (half/full duplex). • Synchronization (checkpoints).

  24. Provisions for efficient data transmission. • Reporting of session, presentation and application layer errors (errors above transport layer).

  25. The transport layer: • services to user’s applications. • Data format. • Dialog and conversations. • End - to - end services. • Segmentation / reassembly : • Reliability : • error recovery • acknowledgment.

  26. Flow control : • Sliding windows. • Establishes , manages and terminates virtual circuits (not physical circuits). • Shields the upper layers from transport details.

  27. The network layer: • services to user’s applications. • Data format. • Dialog and conversations. • Reliability, flow control, error recovery. • IP addressing. • Path selection. • Packet routing.

  28. The data link layer: • services to user’s applications. • Data format. • Dialog and conversations. • Reliability, flow control, error recovery. • Addressing / path selection. • Point –to- point services. • Reliability over the physical link.

  29. Media access control. • Network topology. • Error detection. • Flow control. • Physical addressing. • Framing.

  30. The physical layer: • services to user’s applications. • Data format. • Dialog and conversations. • Reliability, flow control, error recovery. • Addressing / path selection. • Framing, access control. • Binary transmission.

  31. Electrical characteristics of physical medium. • Pin assignment. • Timing of bits. • Voltage levels • Data rate. • Distances. • Encoding schemes.

  32. encapsulation

  33. Encapsulation wraps data with necessary protocol information before transit. header Data Data stream Data stream Data stream Data Data Data header Data header trail (peer-to-peer communication- PDUs) 00111101010011010101011100011001

  34. TCP / IP model

  35. The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions, even a nuclear war. • The main purpose was to move packets from any point to any other point regardless of the condition of any particular node.

  36. The application layer: • Session and Presentation layers are thin. • TCP/IP model combines the functions of the upper three layers into one layer.

  37. The transport layer: • Deals with QoS issues (TCP protocol): • reliability: • Error recovery. • Acknowledgment. • flow control: • Sliding windows. • TCP – connection oriented protocol.

  38. The internet layer: • path determination. • Packet switching. • IP addressing. • Connectionless services (unreliable).

  39. The network-access layer: • Host-network layer. • Combines the functions of physical and data link layers. • It includes the WAN and LAN technology.

  40. TCP / IP protocol graph:

  41. Similarities: • both have layers • both have application layers. • both have comparable transport and network layers • packet-switched (not circuit-switched) technology is assumed • networking professionals need to know both

  42. Differences • TCP/IP combines the presentation and session layer issues into its application layer • TCP/IP combines the OSI data link and physical layers into one layer • TCP/IP appears simpler because it has fewer layers • TCP/IP protocols are the standards around which the Internet developed, so the TCP/IP model gains credibility just because of its protocols. In contrast, typically networks aren't built on the OSI protocol, even though the OSI model is used as a guide. 

  43. data application 4 application presentation 4 application data session 4 application data 3 segment transport transport internet network 2 packet Data link frame 1 Netw. access physical 1 Netw. access bits

  44. Good Luck

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