ch02-OSI Specifications.ppt

Chapter 2: OSI Specifications Click to edit Master subtitle style  Chapter 2 Objectives The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter: 1.2 Explain devices, applications, protocols, and services at their appropriate OSI lay...

Chapter 2: OSI Specifications Click to edit Master subtitle style  Chapter 2 Objectives The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter: 1.2 Explain devices, applications, protocols, and services at their appropriate OSI layers Layer 1 – Physical Layer 2 – Data link Layer 3 – Network Layer 4 – Transport Layer 5 – Session Layer 6 – Presentation Layer 7 – Application 2  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. 3  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. 4  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) 5  OSI Layer Functions File, print, message, database, and application services Application Data encryption, compression, and translation services Presentation Dialog control Session End-to-end connection (Segmentation) Transport Routing Network Framing Data Link Physical topology Physical 6  The Upper Layers Provides a user interface Application Presents data Presentation Handles processing such as encryption Keeps different applications’ Session data separate Transport Network Data Link Physical 7  The Lower Layers Application Presentation Session Provides reliable or unreliable delivery Transport Performs error correction before retransmit Provides logical addressing which routers use for path Network determination Combines packets into bytes and bytes into frames Data Link Provides access to media using MAC address Performs error detection not correction Moves bits between devices Physical Specifies voltage, wire speed, and pin-out of cables 8  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. 9 A Connection Oriented Session Sender Receiver SYN SYN/ACK ACK Connection Established Data transfer (Send bytes of Segments) 10  Flow Control Sender Receiver Transmit Buffer full Not ready – STOP! Segments processed GO! Transmit 11 Windowing Flow Control Sender Receiver Window size of 1 Send 1 Receive 1 Ack 1 Send 2 Receive 2 Ack 2 Window size of 3 Send 1 Send 2 Send 3 Ack 4 Send 4 12  Acknowledgements Sender Receiver 1 2 3 4 5 6 1 2 3 4 5 6 Send 1 Send 2 Send 3 Ack 4 Send 4 Send 5 Connection lost! Send 6 Ack 5 Send 5 Ack 7 13  Routing at Layer 3 3.0 1.0 3.1 1.1 2.1 2.2 1.3 3.3 E0 E0 S0 S0 3.2 1.2 Routing table Routing table NET INT Metric NET INT Metric 1 E0 0 1 S0 1 2 S0 0 2 S0 0 3 S0 1 3 E0 0 14  Routers at Layer 3 Internet FastEthernet0/0 Serial0 WAN Services FastEthernet0/1 Each router interface is a broadcast domain. Routers break up broadcast domains by default and provide WAN services. 15  Data Link Layer (Layer 2) Logical Link Control (LLC) Media Access Control (MAC) 802.11 802.3 802.2 16  Data Encapsulation PDU Application Presentation Upper layer data Session TCP Header Upper layer data Segment Transport IP Header Segment Packet Network LLC Header Packet FCS Frame Data Link MAC Header Packet FCS 0101110101001000010 Bits Physical 17  Summary Summary Exam Essentials Section Written Labs Review Questions 18