Get into Networking by Clearing Comptia Network+ Test
- 1. CompTIA Network + Chapter 2 Dissecting the OSI Model FOR MOR INFORMATION VISIT http://www.certblaster.com/product/network-n10-006-practice-tests/ live
- 2. Objectives What is the purpose of a Network model? What are the layers of the OSI model? What are the characteristics of each layer of the OSI model? How does the TCP/IP stack compare to the OSI model? What are the well-known TCP and/or UDP port numbers for a given collection of common applications
- 3. The Purpose of Reference Models • It breaks network communication into smaller, simpler parts that are easier to develop. • It facilitates standardization of network components to allow multiple-vendor development and support. • It allows different types of network hardware and software to communicate with each other. • It prevents changes in one layer from affecting the other layers so that they can develop more quickly. • It breaks network communication into smaller parts to make learning it easier to understand.
- 4. The OSI seven-layer model Application Presentation Session Transport Network Data Link Physical Figure 2-2 OSI Stack 1 2 3 4 5 6 7
- 5. Mnemonics for the OSI Model Away Pizza Sausage Throw Not Do Please All People Seem To Need Data Processing
- 6. Quick Summary of Layers 1-4 Transport Network Data Link Physical1 2 3 4 TCP & UDP Ports Routers, IP Address Switches, MAC Address Cables Service WAN LAN
- 7. OSI Layers in Wireshark 1 2 3 4 7
- 8. Physical Layer Physical • How Bits are represented on the medium • Wring standards for connectors and jacks • Physical topology • Synchronizing bits • Bandwidth usage • Multiplexing strategy Figure 2-4 Layer 1: Physical Layer
- 9. Bandwidth Usage • Broadband – Multiple channels share the same medium – Ex: cable TV uses frequency division multiplexing (each channel uses a different frequency range) • Baseband – The whole medium is used for one transmission – Example: Ethernet
- 10. ABCA_CABCA_C Time-Division Multiplexing (TDM) • Each channel gets the same amount of time on the wire AAAA B_B_ CCCC
- 11. ABCACABCAC Statistical Time-Division Multiplexing (StatTDM) AAAA B_B_ CCCC • Busy channels get more time on the wire
- 12. Frequency Division Multiplexing (FDM) AAAA B_B_ CCCC • Example: signals sent with different colors through the same fiber optic cable AAAA B_B_ CCCC AAAA B_B_
- 13. Layer 1 Devices • Cables • Wireless access points • Hubs – Because they don’t pay any attention to addresses, they just deliver signals to every connected device like a crossover cable
- 14. Data Link Layer Data Link • Physical Addressing • Logical topology • Method of transmitting on the media Figure 2-8 Layer 2: The Data Link Layer MAC LLC • Connection Services • Synchronizing transmissions
- 15. MAC Addresses • IPCONFIG /ALL • Physical Address • Built into the network interface
- 16. Connection Services • Flow control – Prevents sender from sending data faster than the client can accept it • Error control – When a frame is received, a checksum is used to detect errors • Usually a Cyclic Redundancy Check (CRC) – If the receiver's checksum does not match the sender's checksum, the frame is discarded and resent
- 17. Layer 2 Devices • Switches • Bridges • Network Interface Cards (NICs)
- 18. Network Layer Network • Logical addressing • Switching • Route discovery and selection • Connection services • Bandwidth usage • Multiplexing strategy Figure 2-9 Layer 3: The Network Layer
- 19. IP Address • Logical address • Changes when the device is moved
- 20. Switching • Packet switching – Data is broken into packets – Many packets travel along network connections like cars on a freeway • Circuit switching – A physical line is dedicated to each connection – Ex: old copper landline phone systems • Message switching – Store-and-forward, like email
- 21. Layer 3 Devices • Routers • Multilayer Switches
- 22. Transport Layer Transport • TCP/UDP • Windowing • Buffering Figure 2-10 Layer 4: The Transport Layer
- 23. TCP and UDP • Transmission Control Protocol (TCP) – Connection-oriented and reliable – Handshake makes sure both ends are ready – Segments are acknowledged and resent if necessary • User Datagram Protocol (UDP) – Connectionless and unreliable – No handshake – Best-effort delivery, no acknowledgements
- 24. TCP Sliding Window Figure 2-11 TCP Sliding Window
- 25. ICMP (Internet Control Message Protocol) • At layer 4 • Used by ping and traceroute, and to indicate errors such as dropped packets
- 26. Session Layer Session • Setting up a session • Maintaining a session • Tearing down a session Figure 2-12 Layer 5: The Session Layer
- 27. Example of a Session • User logs in with a username & password • All data now has a special significance until that user logs off, or the session times out, or is terminated some other way • Layer 6 Protocol – H.323 (voice or video) – NetBIOS (file sharing)
- 28. Presentation Layer Presentation • Data formatting • Encryption Figure 2-13 Layer 6: The Presentation Layer
- 29. Application Layer Application • Application services • Service advertisement
- 30. Application Layer • Closest to the user • Hands data to an application in the format it expects, with no addresses or other transmission artifacts • Examples: a downloaded file, an email message
- 31. The TCP/IP Stack Application Transport Internet Network Interface
- 32. The TCP/IP and OSI Models Compared Application Transport Internet Network Interface TCP/IP Stack Application Presentation Session Transport Network Data Link Physical OSI Stack Figure 2-15 TCP/IP Stack
- 33. IP Ver4 Header
- 34. TTL (Time-to-Live) • TTL decreases by one each time the packet is forwarded by a router • If TTL reaches zero, the packet is discarded • This eliminates packets trapped in routing loops
- 36. TCP Header Figure 2-17 TCP Segment Format
- 37. TCP Header Fields • Port numbers – Indicate which program on the end device should receive the data – Examples: Port 25 for email, 80 for HTTP • Window size – Number of bytes that can be sent before waiting for an ACK
- 38. TCP Header Fields • Sequence and Acknowledgement numbers – Used to put packets in order to reassemble files and other large messages • Flags like SYN and ACK are used for the TCP handshake and to acknowledge data received
- 39. UDP Header 0 16 31 SOURCE PORT DESTINATION PORT LENGTH CHECKSUM • No handshake, acknowledgements, sequencing, or flow control
- 40. Common Ports Link Ch 2d for flash cards
- 41. Port Types Port numbers are assigned in various ways, based on three ranges: System Ports (0-1023), System Ports are assigned by IETF process for standards-track protocols, as per RFC6335. Also known as well-known- ports User Ports (1024-49151) ,User Ports are assigned by IANA using the "Expert Review" process, as per RFC6335 Dynamic and/or Private Ports (49152-65535), Dynamic Ports are not assigned, they are dynamically created as your computer need them. Also known as ephemeral ports.
- 42. Communication Between Two Systems