|  | 8.2 | Understand Physical Layer
| 8.2.1 | Troubleshooting the Physical Layer when you have network problems after installing or replacing a NIC.
After installing or replacing a NIC and experiencing problems accessing the network, it is important to troubleshoot the NIC and follow a logical troubleshooting methodology. Determine which areas are affected. Identify what caused the problem: A protocol or a device. Identify the differences of the affected areas and the unaffected areas. Restart the affected hardware. Often the problem can be resolved if the hardware of the affected area is restarted. Divide the network in half and segment the area. Lastly, if the problem can not be identified by any of these methods, physical tools, from technical databases to diagnostics, may be necessary. A form of technical diagnostics includes testing called loopback testing. Either an external loopback adapter or an internal device is attached to the NIC. Data is sent from the NIC out and looped back in to verify if the data received is the same as the data, which was sent out. Vendor supplied diagnostics programs are usually available through a vendor's webpage or technical support service. The following questions are information that a network installer must understand to properly diagnose NIC card problems. Question 1: What does the EPROM on a NIC do? In the Erasable Programmable Read Only Memory (EPROM) is a set of instructions, which is built into a network adapter that allows the NIC to perform its basic functions. In a diskless workstation, commonly in larger networks, the EPROM is often replaced by a PROM. The code in the PROM is unalterable and boots a workstation that has no hard disk or diskette; this feature can be added to the NIC in order that the system can be enabled to boot using files stored on the network. Question 2: What do jumpers on a NIC do? Jumpers are pieces of plastic and metal that connect two metal posts on a NIC and are most commonly used to change a NIC's configuration, mainly the IRQ and the I/O addresses. Because NICs have multiple connection options, jumpers determine which transceiver needs to be used on the NIC, which transceiver to hook the cable to, and the data rate transfer setting. Question 3: What does plug and play software (usually packaged with NICs) do? Plug and Play works with the plug and play BIOS to configure expansion components on a system, such as a NIC and other devices. Plug and Play allows the user to have minimal, if any, configuration issues when installing a device. Question 4: What are network card diagnostics, such as the loopback test and vendor-supplied diagnostics? When troubleshooting a network, there are two diagnostics that can be used. First, there is the loopback test, which tests the in-bound and out-bound communications of a NIC. In an external loopback test, a signal is sent from the NIC, out through an adapter, then sent back into the NIC. The information is then verified to determine if the information received is the same as what was sent out. Internal loopback tests use the same idea; however, no external adapter is used. The second method in troubleshooting a NIC is using vendor-supplied diagnostic programs. Normally, the manufacturers of a NIC will provide specific tests that can troubleshoot a NIC. There are generic diagnostics available; however the vendor-supplied diagnostics tests is usually more reliable. These programs can be retrieved from either the vendor's technical support lines or webpages. Question 5: What does it mean to resolve hardware resource conflicts, including IRQ, DMA, and I/O Base Address? Because there are many devices in a personal computer, hardware conflicts may arise when one device tries to communicate to another within a computer. To avoid such conflicts, there are three main ways for devices to communicate to another within a computer. Interrupt Request (IRQ) is a method, where a device can interrupt the processor and request a service. In a PC there are 16 IRQ lines available and dedicated to devices, such as disk controllers, serial, and parallel ports. Some of the more common IRQs are IRQ 3 (for serial port COM port 2) and IRQ 5 or 10 (dedicated to NICs). In general, IRQs can not be assigned to more than one device at a time, or a conflict will occur. Direct Memory Access (DMA) is a method, whereby devices can access the computer's memory without involving the CPU. DMA is managed by the DMA controller chip, which is generally faster than the CPU, and works as if the CPU had managed the transfer of memory itself. I/O (input/output) Base Addresses allows the CPU to be able to access each device in the computer. Each device is assigned a unique I/O address that can not be shared. If there are more than one device containing the same I/O address, neither device will be able to function properly. The CPU will attempt to send information to the specified I/O address; however, because two devices are assigned the same address, both will respond and the data will be corrupted.