tailieunhanh - CompTIA Network+ Certification Study Guide part 55

CompTIA’s Network+ certification Study Guide part 55 is a globally-recognized, vendor neutral exam that has helped over 235,000 IT professionals reach further and higher in their careers. The 2009 Network+ exam (N10-004) is a major update with more focus on security and wireless aspects of networking. Our new study guide has been updated accordingly with focus on network, systems, and WAN security and complete coverage of today’s wireless networking standards. | 526 CHAPTER 11 Network Troubleshooting Tools own header to the packet. When a network packet is passed from one host to another the receiving host will read or analyze the packet one layer at a time with the application layer reading the application layer header the presentation layer reading the header from the presentation layer and so forth. You can use your understanding of the OSI model to improve your troubleshooting techniques. It s important to understand what takes place at each layer of the OSI model and which devices operate at these layers. When it comes to network troubleshooting the most important layers of the model are the physical data link network and transport layers. Let s take a look at each of these layers in turn. Note We are only going to touch on the function of each layer here - refer back to previous chapters for an in-depth look at the layers of the OSI model. The Physical Layer The physical layer is the lowest layer of the OSI model and it involves the actual electrical signals that are going from the network cables into the NIC of a computer switch router or hub. A failure at the hardware level will usually involve the physical components of a computer or device such as the cable that connects the computer to the network or the network card itself. Network hubs also operate at the physical layer so a failure in a network hub could also lead to connectivity issues that occur at the physical layer. The physical layer is responsible for a number of different functions including The type of signal transmission used The cable type The actual layout or path of the network wiring The voltage and electrical signals being used by the network cabling When using the OSI model for troubleshooting you should know which devices operate at which layer. The following physical devices function at the physical layer of the OSI model Network cabling Network interface cards Active and passive hubs Repeaters The OSI Model 527 When troubleshooting at the .