Explaining the OSI and TCP/IP Models Explaining the OSI and TCP/IP Models • Explain OSI Model Layers • Explain the TCP/IP Suite Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 2 Topic A: Explain OSI Model Layers Exam Objectives: • 1.2 Explain devices, applications, protocols, and services at their appropriate OSI layers. • 1.3 Explain the concepts and characteristics of routing and switching. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 3 Network Boundaries • Two or more computer systems linked by transmission media to share information • Networks are built to provide useful services • • • • Sharing data and resources Email and database applications Web applications and social networking Voice and multimedia conferencing • Local Area Network (LAN) • Wide Area Network (WAN) Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 4 Open Systems Interconnection (OSI) Model Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 5 Protocol Data Units (PDUs) • Rules for exchanging data • Addressing • Encapsulation • Header • Payload Image © 123RF.com. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 6 Layer 1 (Physical) (Slide 1 of 2) • Nodes, stations, and hosts • A node is a device communicating on the network via one or more interfaces • Can include endpoints such as computers • Can include forwarding nodes such as switches and routers • Station can be used instead of node when talking about wireless networks • Host typically refers to a computing device (not a switch or a router) • Transmission media: cabled or wireless links between nodes • Physical topology Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 7 Layer 1 (Physical) (Slide 2 of 2) • Mechanical specifications for the network medium • Cable specifications • Connector form factor and pin-outs • Radio transceiver specifications • Signaling (bit transmission/encoding) • Devices • • • • Transceiver Media converter Hub/repeater Modem Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 8 Layer 2 (Data Link) (Slide 1 of 2) • Local network devices • Nodes that forward communications within the same physical network (switching) • Physical/local addresses • Organize bits into frames • Destination and source hardware addresses • Media Access Control (MAC) address • Error detection • Flow control • Media access rules/logical topology • Contention (logical bus topology) • Token-passing (logical ring topology) Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 9 Layer 2 (Data Link) (Slide 2 of 2) Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 10 Layer 2 Devices • Network adapter or network interface card (NIC) • Bridge • Basic switch • Wireless access point (AP) Image © 123RF.com. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 11 IEEE 802 Standards (Slide 1 of 2) Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 12 IEEE 802 Standards (Slide 2 of 2) • 802.2 (Logical Link Control sublayer) • Provides standard interface for Network layer, regardless of the MAC sublayer protocol • 802.3 (Media Access Control sublayer) or Ethernet • • • • • • Logical topology Media access method Hardware (MAC) addresses Frame format Error checking Physical layer (signaling and media) specifications Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 13 Layer 3 (Network) • Moving data around a network of networks (internetwork/the Internet) • Logical addressing between networks • Routing • Route discovery • Path selection • Devices • Router • Layer 3 switch • Basic firewall Image © 123RF.com. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 14 Switching vs. Routing Components • • • • • WAN router/firewall LAN router Subnetworks Switches Backbones Image © 123RF.com. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 15 Layer 4 (Transport) (Slide 1 of 2) • Multiplexing and de-multiplexing • • • • Identifies application data via port numbers Packages data in a stream of segments Merges segments from different applications over the network link Port numbers allow receiving host to de-multiplex and reassemble data for the appropriate application handler • Reliable delivery • • • • Connection establishment Acknowledgements and negative acknowledgments Segmentation and sequencing Flow control Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 16 Layer 4 (Transport) (Slide 2 of 2) • Unreliable (connectionless) delivery • Devices: • Multilayer switches • Security appliances like advanced firewalls and IDSs Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 17 Session and Presentation Layers • Divisions between upper layers less important in real-world protocols • Layer 5 (Session) • Identify a sequence of messages belonging to the same “conversation” • Dialog control (simplex, half-duplex, or duplex) • Layer 6 (Presentation) • Character set conversion • Compression and decompression support • Encryption and decryption support Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 18 Layer 7 (Application) • Doesn’t encapsulate another protocol • Top of the stack • Provides communications protocols and interfaces for software processes running on different hosts • Application layer versus software implementation of network functions • Application programming interfaces (APIs) for software programs • APIs can be written for any layer of the stack • Network card drivers (e.g., NDIS) at layer 2 (Data Link) • Sockets/WinSock at layer 5 (Session) • High-level API functions (file transfer, email, web browsing, and DNS) at layer 7 Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 19 OSI Model Summary Image © 123RF.com. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 20 Activity Discussing OSI Model Layers Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 21 Topic B: Explain the TCP/IP Suite Exam Objectives: • 1.3 Explain the concepts and characteristics of routing and switching. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 22 TCP/IP Protocol Suite Image © 123RF.com. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 23 TCP/IP Model Layers • Link/Network Interface layer • Ethernet/Wi-Fi • WAN • Internet layer • Fragmentation • IP and ARP • Transport layer • TCP and UDP • Application layer Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 24 Packet-Switched vs. Circuit-Switched Networks • Rather than establish a circuit, data is broken into packets that can take any path to their destination • Robust as can recover from link failures Image © 123RF.com. Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 25 TCP/IP and Internet Standards • Internet Society (ISOC) • Internet Architecture Board (IAB) • Internet Engineering Task Force (IETF): Internet and web standards • Internet Assigned Numbers Authority (IANA) • IP address allocations and DNS (Domain Name System) • Regional Registries and Internet Service Providers (ISPs) • Function of the IANA is contracted to the Internet Corporation for Assigned Names and Numbers (ICANN) • Requests For Comments (RFCs) Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 26 Activity Discussing the TCP/IP Suite Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 27 Reflective Questions 1. How will knowing the OSI model help you perform networking tasks? 2. What is your experience with network components? Copyright © 2019 CompTIA Properties, LLC. All Rights Reserved. | CompTIA.org 28
