The network interface adapter (called the NIC when installed in a computer'sexpansion 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 an interface to the networkmedium. Some computers have the network interface adapter integrated into the motherboard, but in most cases the adapter takes the form of an expansion card that plugs into the system's Industry Standard Architecture (ISA), Peripheral Component Interconnect (PCI), or PC Card bus. An ISA-bus NIC is illustrated in Figure 2.11. The network interface itself is, in most cases, a cable jack such as an RJ45 for UTP cables or a BNC or AUI connector for a coaxial cable connection, but it can also be a wireless transmitter of some sort.
Figure 2.11 Network interface adapters usually take the form of expansion cards
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 the physical layer. When you buy a NIC for a computer, you must select one for a particular data-link layer protocol, such as Ethernet or Token Ring; they are not interchangeable. You must also be sure to select a NIC that supports the specific variant of your data-link layer protocol. In the case of twisted-pair Ethernet, for example, a NIC can support standard Ethernet, Fast Ethernet (100Base-TX or 100Base-T4), Full-Duplex Fast Ethernet, or 1000Base-T Gigabit Ethernet. You must also select a card that plugs into the appropriate type of bus slot in the computer and has the proper connector for the network medium.
Not all network interface adapters are intended to connect computers to standard client/server LANs. There are also NICs available that connect computers and other devices to a specialized network called a Storage Area Network (SAN). A SAN is a separate network dedicated to communications between servers and external storage devices, such as redundant array of independent disks (RAID) arrays. Most SAN adapters use a protocol called Fibre Channel rather than one of the standard LAN protocols, such as Ethernet and Token Ring.
Network interface cards that plug into a PCI bus slot 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. For portable systems, the PC Card bus is usually your only choice, but you should be sure to purchase a NIC that supports the CardBus standard if your computer supports it. CardBus is an interface specification that provides the equivalent of PCI performance to PC Card peripherals. There are also network interface adapters on the market that plug into a computer's universal serial bus (USB) port, but the USB interface runs at a maximum of 1.2 Mbps and provides relatively poor performance, even when compared to ISA. You should always ensure that the data rate of the NICs you select is compatible with the other network components.
Network interface cards have different network cable connectors depending on the types of cables they support. Some NICs have more than one cable connector, which enables you to connect to different types of network media. For example, it is common to find combination Ethernet NICs with as many as three cable connectors (RJ45, BNC, and AUI), especially in small stores that would rather stock a single card instead of three different ones. You can only use one of the connectors at a time, however, and these combination NICs can be much more expensive than those with only one connector.
One of the few scenarios in which combination NICs are practical is when several cards are needed for an internetwork that uses multiple cable types and it is cheaper to buy the NICs in quantity. Many NIC manufacturers sell their products in multiunit packs that are deeply discounted.
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 NIC consists of physically inserting the card intothe 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 NICInstallation video located in the Demos folder on theCD-ROM accompanying this book for a demonstration of a NIC installation.
Before touching the internal components of the computer or removing the NIC from its protective bag, be sure to ground yourself by touching the metal frame of the computer's power supply, or use a wrist strap or static-dissipative mat to protect the equipment from damage due to electrostatic discharge.
To physically install the NIC, follow these steps:
It's usually a good idea to fully test the network card by connecting it to the LAN and running it before you close the case and return the computer to its original location. It seems that newly installed components are more likely to malfunction if you put the cover on before testing them.
The procedure just described 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.
Figure 2.12 Press the NIC down firmly until it is seated all the way into the slot
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 impossible. Every network interface adapter requires an IRQ and an I/O port address 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 in which Plug and Play doesn't quite work as advertised. Improper network interface adapter configuration is one of the main reasons a computer fails to communicate with the network, so knowing how to troubleshoot this problem is a useful skill.
For a network interface adapter (or any type of adapter) to communicate with the computer in which it is installed, the hardware (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 the person they expected. In addition, if the network interface adapter is configured to use the same resources as another device in the computer, both of the conflictingdevices are likely to malfunction.
On older NICs, you configure the hardware resources by installing jumper blocks or setting Dual Inline Package (DIP) switches. If you are working with a card like this, you must configure the card before you install it in the computer. In fact, you may have to remove the card from the slot to reconfigure it if you find that the settings you've chosen are unavailable. Newer 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, 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 might 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 running an operating system like Microsoft Windows XP, Microsoft Windows 2000, Microsoft Windows 98, Microsoft Windows 95, or Microsoft Windows Me, you have better tools to help you resolve hardware resource conflicts. The Device Manager utility (illustrated in Figure 2.13) 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.
Figure 2.13 The Windows 2000 Device Manager utility
The device driver is an integral part of the network interface adapter, as it enables the computer to communicate with the adapter and implements many of therequired functions. Virtually all network interface adapters come with driver software to support all of the major operating systems, but in many cases you won't even need the software because operating systems like Windows include a collection of drivers for most 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 software 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 adapter manufacturer's Web site. However, it 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 an appropriate time 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. Either there is 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. Before you do this, however, 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 available. After exhausting all of these avenues, try installing a different card in the computer. You can use 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.