OSI REFRENCE MODEL by- Mujmmil Shaikh
4 likes3,397 views
The OSI model was developed by the ISO to standardize network communication, enabling different networks to connect and work together. It consists of seven layers, each with specific functions, ranging from the physical transmission of bits to the application layer handling network applications. Understanding the OSI model is essential for network professionals as it provides a framework for troubleshooting and designing robust networking solutions.
OSI REFRENCE MODEL by- Mujmmil Shaikh
- 2. Why do we need the OSI Model? To address the problem of networks increasing in size and in number, the International Organization for Standardization (ISO) researched many network schemes and recognized that there was a need to create a network model This would help network builders implement networks that could communicate and work together ISO therefore, released the OSI reference model in 1984. 2
- 3. Don’t Get Confused. ISO - International Organization for Standardization OSI - Open System Interconnection IOS - Internetwork Operating System To avoid confusion, some people say ―International Standard Organization.” 3
- 4. The OSI Reference Model 7 Application The OSI Model will be used throughout your 6 Presentation entire networking career! 5 Session 4 Transport 3 Network Memorize it! 2 Data Link 1 Physical 4
- 5. OSI Model Application Application (Upper) Presentation Layers Session Transport Network Data Flow Layers Data-Link Physical 5
- 6. Layer 7 - The Application Layer 7 Application This layer deal with 6 Presentation networking applications. 5 Session Examples: 4 Transport Email Web browsers 3 Network 2 Data Link PDU - User Data 1 Physical Each of the layers have Protocol Data Unit (PDU) 6
- 7. Layer 6 - The Presentation Layer 7 Application This layer is responsible for presenting the data in the 6 Presentation required format which may 5 Session include: 4 Transport Code Formatting Encryption 3 Network Compression 2 Data Link PDU - Formatted Data 1 Physical 7
- 8. Layer 5 - The Session Layer 7 Application This layer establishes, manages, and terminates sessions between two communicating hosts. 6 Presentation Creates Virtual Circuit Coordinates communication between systems 5 Session Organize their communication by offering three different modes 4 Transport Simplex Half Duplex 3 Network Full Duplex 2 Data Link Example: 1 Physical Client Software ( Used for logging in) PDU - Formatted Data 8
- 9. Half Duplex • It uses only one wire pair with a digital signal running in both directions on the wire. • It also uses the CSMA/CD protocol to help prevent collisions and to permit retransmitting if a collision does occur. • If a hub is attached to a switch, it must operate in half- duplex mode because the end stations must be able to detect collisions. • Half-duplex Ethernet—typically 10BaseT—is only about 30 to 40 percent efficient because a large 10BaseT network will usually only give you 3 to 4Mbps—at most. 9
- 10. Full Duplex In a network that uses twisted-pair cabling, one pair is used to carry the transmitted signal from one node to the other node. A separate pair is used for the return or received signal. It is possible for signals to pass through both pairs simultaneously. The capability of communication in both directions at once is known as full duplex. 10
- 11. Layer 4 - The Transport Layer 7 Application This layer breaks up the data from the sending host and then reassembles it in the 6 Presentation receiver. 5 Session It also is used to insure reliable data transport across the network. 4 Transport Can be reliable or unreliable Sequencing 3 Network Acknowledgment Retransmission 2 Data Link Flow Control 1 Physical PDU - Segments 11
- 12. Layer 3 - The Network Layer Sometimes referred to as the ―Cisco Layer‖. 7 Application End to End Delivery Provide logical addressing that routers use for 6 Presentation path determination Segments are encapsulated 5 Session Internetwork Communication Packet forwarding 4 Transport Packet Filtering Makes “Best Path Determination” 3 Network Fragmentation 2 Data Link PDU – Packets – IP/IPX 1 Physical 12
- 13. Layer 2 - The Data Link Layer Performs Physical Addressing 7 Application This layer provides reliable transit of data across a physical link. 6 Presentation Combines bits into bytes and bytes into frames 5 Session Access to media using MAC address Error detection, not correction 4 Transport LLC and MAC Logical Link Control performs Link establishment 3 Network MAC Performs Access method 2 Data Link 1 Physical PDU - Frames Preamble DMAC SMAC Data length DATA FCS 13
- 14. Layer 1 - The Physical Layer 7 Application This is the physical media 6 Presentation through which the data, 5 Session represented as electronic signals, is sent from the source host to 4 Transport the destination host. 3 Network Move bits between devices 2 Data Link Encoding PDU - Bits 1 Physical 14
- 15. Data Encapsulation Application Presentation PDU Upper-Layer Data Session Transport Segment TCP HeaderUpper-Layer Data Network Packet IP Header Data LLC Header Data FCS Data-Link Frame MAC Header Data FCS Physical Bits 0101110101001000010 15
- 16. Data Encapsulation 16
- 17. OSI Model Analogy Application Layer - Source Host After riding your new bicycle a few times in Bangalore, you decide that you want to give it to a friend who lives in DADAR, Mumbai. 17
- 18. OSI Model Analogy Presentation Layer - Source Host Make sure you have the proper directions to disassemble and reassemble the bicycle. 18
- 19. OSI Model Analogy Session Layer - Source Host Call your friend and make sure you have his correct address. 19
- 20. OSI Model Analogy Transport Layer - Source Host Disassemble the bicycle and put different pieces in different boxes. The boxes are labeled “1 of 3”, “2 of 3”, and “3 of 3”. 20
- 21. OSI Model Analogy Network Layer - Source Host Put your friend's complete mailing address (and yours) on each box.Since the packages are too big for your mailbox (and since you don’t have enough stamps) you determine that you need to go to the post office. 21
- 22. OSI Model Analogy Data Link Layer – Source Host Bangalore post office takes possession of the boxes. 22
- 23. OSI Model Analogy Physical Layer - Media The boxes are flown from Bangalore to Mumbai. 23
- 24. OSI Model Analogy Data Link Layer - Destination Dadar post office receives your boxes. 24
- 25. OSI Model Analogy Network Layer - Destination Upon examining the destination address, Dadar post office determines that your boxes should be delivered to your written home address. 25
- 26. OSI Model Analogy Transport Layer - Destination Your friend calls you and tells you he got all 3 boxes and he is having another friend named BOB reassemble the bicycle. 26
- 27. OSI Model Analogy Session Layer - Destination Your friend hangs up because he is done talking to you. 27
- 28. OSI Model Analogy Presentation Layer - Destination BOB is finished and “presents” the bicycle to your friend. Another way to say it is that your friend is finally getting him “present”. 28
- 29. OSI Model Analogy Application Layer - Destination Your friend enjoys riding his new bicycle in Dadar. 29
- 30. Data Flow Through a Network 30
- 32. Type of Transmission 32
- 33. Broadcast Domain A group of devices receiving broadcast frames initiating from any device within the group Routers do not forward broadcast frames, broadcast domains are not forwarded from one broadcast to another. 33
- 34. Collision The effect of two nodes sending transmissions simultaneously in Ethernet. When they meet on the physical media, the frames from each node collide and are damaged. 34
- 35. Collision Domain The network area in Ethernet over which frames that have collided will be detected. Collisions are propagated by hubs and repeaters Collisions are Not propagated by switches, routers, or bridges 35
- 36. Physical Layer Defines • Media type 802.3 Physical • Connector type • Signaling type 802.3 is responsible for LANs based on the carrier sense multiple access collision detect (CSMA/CD) access methodology. Ethernet is an example of a CSMA/CD network. 36
- 37. Physical Layer: Ethernet/802.3 10Base2—Thin Ethernet 10Base5—Thick Ethernet Host Hub 10BaseT—Twisted Pair Hosts 37
- 38. Device Used At Layer 1 Physical A B C D • All devices are in the same collision domain. • All devices are in the same broadcast domain. • Devices share the same bandwidth. 38
- 39. Hubs & Collision Domains • More end stations means more collisions. • CSMA/CD is used. 39
- 40. Layer 2 MAC Layer—802.3 Number of Bytes 8 6 6 2 Variable 4 Preamble Destination Address Source Address Length Data FCS Ethernet II uses “Type” here and 0000.0C xx.xxxx does not use 802.2. IEEE Assigned Vendor Assigned MAC Address synchronize senders and receivers 40
- 41. Devices On Layer 2 (Switches & Bridges) Data-Link 1 2 3 4 OR 1 2 • Each segment has its own collision domain. • All segments are in the same broadcast domain. 41
- 42. Switches Switch Memory • Each segment is its own collision domain. • Broadcasts are forwarded to all segments. 42
- 43. Layer 3 : Network Layer Network IP, IPX • Defines logical source and destination Data-Link addresses associated 802.2 with a specific protocol • Defines paths through network 802.3 Physical EIA/TIA-232 V.35 43
- 44. Layer 3 : (cont.) Network Layer End-Station Packet Source Destination IP Header Data Address Address Logical Address 172.15.1.1 Network Node Route determination occurs at this layer, so a packet must include a source and destination address. Network-layer addresses have two components: a network component for internetwork routing, and a node number for a device-specific address. The example in the figure is an example of an IP packet and address. 44
- 45. Layer 3 (cont.) Address Mask 172.16.122.204 255.255.0.0 172 16 122 204 Binary Address 10101100 00010000 01111010 11001100 255 255 0 0 Binary Mask 11111111 11111111 00000000 00000000 Network Host 45
- 46. Device On Layer 3 Router • Broadcast control • Multicast control • Optimal path determination • Traffic management • Logical addressing • Connects to WAN services 46
- 47. Layer 4 : Transport Layer • Distinguishes between upper-layer applications • Establishes end-to-end Transport connectivity between TCP UDP SPX applications • Defines flow control Network IP IPX • Provides reliable or unreliable services for data transfer 47
- 48. Reliable Service Sender Receiver Synchronize Acknowledge, Synchronize Acknowledge Connection Established Data Transfer (Send Segments) 48
- 49. How They Operate Hub Bridge Switch Router Collision Domains: 1 4 4 4 Broadcast Domains: 1 1 1 4 49