Figure 2.7 Network interface adapters usually take the form of expansion cards.
The network interface adapter (called the network interface card, or NIC, when installed in a computer's expansion slot) is the component that provides the link between a computer and the network of which it is a part. Every computer must have an adapter that connects to the system's expansion bus and provides a connection to the network medium. Some computers have the network interface adapter integrated into the motherboard, but in the majority of cases the adapter takes the form of an expansion card that plugs into the system's ISA, PCI, or PC Card bus. An ISA-bus network interface card is illustrated in Figure 2.7. The network connection is, in most cases, a cable jack such as an RJ45 for UTP cables, but it can also be a wireless transmitter of some sort.
The network interface adapter, in cooperation with its device driver, is responsible for performing most of the functions of the data-link layer protocol, and those of the physical layer. When you buy a NIC for a computer, you must select one for a particular protocol, such as Ethernet or Token Ring; they are not interchangeable. You must also select a card that plugs into the appropriate type of bus slot in the computer, and that has the proper connector for the network medium. PCI cards are generally preferable, because the slots are self-configuring and the bus is much faster than ISA, but you may use an ISA card if the computer has only ISA slots available. Ensure that the data rate of the card is compatible with the other network components. Some NICs have more than one cable connector, which enables you to connect to different types of network media, but these combo NICs can be much more expensive than those with only one connector.
Network interface adapters perform a variety of functions that are crucial to getting data to and from the computer over the network. These functions are as follows:
The process of installing a network interface card consists of physically inserting the card into the computer, configuring the card to use appropriate hardware resources, and installing the card's device driver. Depending on the age and capabilities of the computer, these processes can be very simple or quite a chore.
Run the c02dem17 and c02dem18 videos located in the Demos folder on the CD-ROM accompanying this book for a demonstration of a NIC installation.
The procedure described above is for installing a NIC into a standard expansion slot on a desktop computer. If you are working with a laptop, the network interface adapter takes the form of a PC Card, which you install simply by inserting it into a PC Card slot from the outside of the computer.
Configuring a network interface adapter is a matter of configuring it to use certain hardware resources, such as the following:
Network interface adapters do not usually use memory addresses or DMA channels, but this is not beyond the realm of possibility. Every network interface adapter requires an IRQ and an I/O port address in order to communicate with the computer.
When you have a computer and a network interface adapter that both support the Plug and Play standard, the resource configuration process is automatic. The computer detects the adapter, identifies it, locates free resources, and configures the adapter to use them. However, it is important for a network support technician to understand more about the configuration process, because you may run into computers or network interface adapters that do not support Plug and Play, or you may encounter situations where Plug and Play doesn't quite work as advertised. Improper network interface adapter configuration is one of the main reasons that a computer fails to communicate with the network, and knowing how to troubleshoot this problem is a useful skill.
In order for a network interface adapter (or any type of adapter) to communicate with the computer in which it is installed, the hardware (that is, the adapter) and the software (the adapter driver) must both be configured to use the same resources. Before the availability of Plug and Play, this meant that you had to configure the network interface adapter itself to use a particular IRQ and I/O port, and then configure the network interface adapter driver to use the same settings. If the settings of the network interface adapter and the driver do not match, it's like dialing the wrong number on a phone; the devices are speaking to someone, but it isn't who they expected. In addition, if the network interface adapter is configured to use the same resources as another device in the computer, then both of the conflicting devices are likely to malfunction.
On older NICs, you configure the hardware resources by installing jumper blocks or setting DIP switches. If you are working with a card like this, you must configure the card before you install it into the computer. In fact, you may have to remove the card from the slot in order to reconfigure it if you find that the settings you've chosen are unavailable. Later model NICs use a proprietary software utility supplied by the manufacturer to set the card's resource settings. This makes it easier to reconfigure the settings in the event of a conflict. The Plug and Play cards available today usually include a configuration utility also, but you won't need to use it unless your computer doesn't properly support Plug and Play.
When you're working with older equipment, determining the right resource settings for the NIC can be a trial-and-error process. Older NICs often have a relatively limited number of available settings, and you may have to try several before you find a configuration that works. Newer cards have more settings to choose from, and when you're working with a newer computer that's running an operating system like Windows 2000, Windows 98, Windows 95, or Windows Me, you have better tools to help you resolve hardware resource conflicts. The Device Manager utility (illustrated in Figure 2.9) lists the resource settings for all of the components in the computer, and can even inform you when a newly installed NIC is experiencing a resource conflict. You can use Device Manager to find out which device the NIC is conflicting with and which resource you need to adjust.
The device driver is an integral part of the network interface adapter, as it enables the computer to communicate with the network interface adapter and implements many of the required functions. Virtually all network interface adapters come with a driver disk supporting all of the major operating systems, but in many cases you won't even need the disk, because operating systems like Windows include a collection of drivers for most of the popular network interface adapter models.
In addition to configuring the network interface adapter's hardware resource settings, Plug and Play also installs the appropriate driver, assuming that the operating system includes one. If it doesn't, you'll have to supply the driver disk included with the card. Like any piece of software, network interface adapter drivers are upgraded from time to time, and you can usually obtain the latest driver from the network interface adapter manufacturer's Web site. However, it usually is not necessary to install every new driver release unless you're experiencing problems and the new driver is designed to address those problems. In other words, network interface adapter drivers are usually subject to the "if it's not broken, don't fix it" rule.
When a computer fails to communicate with the network, the network interface adapter can conceivably be at fault, but it's far more likely that some other component is causing the problem. Before addressing the network interface adapter itself, check for the following alternative problems first:
If you can find no problem with the driver, the cable, or the network configuration parameters, it's time to start looking at the NIC itself. Before you open the computer case, check to see if the NIC manufacturer has provided its own diagnostic software. In some cases, the same utility you use to configure the NIC's hardware resources manually also includes diagnostic features that test the functions of the card. If you're using Plug and Play, you might not have even looked at the disk included with the NIC, but this is a time when it can be worth your while to do so. In troubleshooting a hardware component like this, you should exhaust all other options before you actually open the computer.
If the NIC diagnostics indicate that the card is functioning properly, and assuming that the software providing the upper layer protocols is correctly installed and configured, the problem you're experiencing is probably caused by the hardware resource configuration. There is either a resource conflict between the network interface adapter and another device in the computer, or the network interface adapter is not configured to use the same resources as the network interface adapter driver. Use the configuration utility supplied with the adapter to see what resources the network interface adapter is physically configured to use, and then compare this information with the driver configuration. You may have to adjust the settings of the card or the driver, or even those of another device in the computer, to accommodate the card.
If the diagnostics program finds a problem with the card itself, it is time to open up the computer and physically examine the NIC. If the NIC is actually malfunctioning, due to a static discharge or a manufacturer's defect, for example, there is not much you can do except replace it. However, before you do this, you should check to see that the NIC is fully seated in the slot, as this is a prime cause of communication problems. If the card is not secured with a screw, press it down firmly into the slot at both ends and secure it. If the problem persists, try removing the card from the slot, cleaning out the slot with a can of compressed air, and installing the card again. If there is still a problem, you can try using another slot, if one is available. After exhausting all of these avenues, trying installing a different card in the computer, either a new one or one from another computer that you know is working properly. If the replacement card functions, then you know that the card itself is to blame, and you should obtain a replacement.
