Lesson 2:Network Interface Adapters

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


After this lesson, you will be able to

  • Describe the functions of a network interface adapter
  • List the various types of NICs on the market
  • Understand the NIC installation and troubleshooting process

Estimated lesson time: 20 minutes


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.

Understanding Network Interface Adapter Functions

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:

  • Data encapsulation.  The network interface adapter and its driver areresponsible for building the frame around the data generated by the network layer protocol in preparation for transmission. The network interface adapter also reads the contents of incoming frames and passes the data to the appropriate network layer protocol.
  • Signal encoding and decoding.  The network interface adapter implements the physical layer encoding scheme that converts the binary data generated by the network layer—now encapsulated in the frame—into electrical voltages, light pulses, or whatever other signal type the network medium uses, and converts received signals to binary data for use by the upper layer protocols.
  • Data transmission and reception.  The primary function of the network interface adapter is to generate and transmit signals of the appropriate type over the network and to receive incoming signals. The nature of the signals depends on the network medium and the data-link layer protocol. On a typical LAN, every computer receives all of the packets transmitted over the network, and the network interface adapter examines the data-link layer destination address in each packet to see if it is intended for that computer. If so, the network interface adapter passes the packet to the computer for processing by the next layer in the protocol stack; if not, the network interface adapter discards the packet.
  • Data buffering.  Network interface adapters transmit and receive data one frame at a time, so they have built-in buffers that enable them to store data arriving either from the computer or from the network until a frame is complete and ready for processing.
  • Serial/parallel conversion.  The communication between the computer and the network interface adapter usually runs in parallel (that is, either 16 or 32 bits at a time), depending on the bus the adapter uses. (Only USB adapters communicate with the computer serially.) Network communications, however, are serial (running one bit at a time), so the network interface adapter is responsible for performing the conversion between the two types of transmissions.
  • Media Access Control (MAC).  The network interface adapter also implements the MAC mechanism that the data-link layer protocol uses to regulate access to the network medium. The nature of the MAC mechanism depends on the protocol used.

Installing a NIC

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:

  1. Turn off the power to the computer. Inserting a NIC in a slot while the computer is on can destroy the NIC. Accidentally dropping a screw or slot cover can also cause serious damage if the computer is powered up.
  2. Open the computer case. In some instances, this can be the most difficult part of the installation process. You may have to remove several screws to loosen the case cover and wrestle with the computer a bit to get the cover off. Many newer systems, on the other hand, secure the case cover with thumbscrews and are much easier to open.
  3. Locate a free slot. There are both ISA and PCI NICs on the market, and you must check to see what type of slots the computer has available before you select a card. An ISA card is sufficient for average network use, but this busis gradually being phased out and replaced by PCI. The PCI bus is preferable if you are planning to connect the computer to a Fast Ethernet or other100-Mbps network.
  4. Remove the slot cover. Empty slots are protected by a metal cover that prevents them from being exposed through the back of the computer. Loosen the screw securing the slot cover in place, and remove both the screw and slot cover.
  5. Insert the card into the slot. Line up the edge connector on the card with the slot and press it down until it is fully seated, as shown in Figure 2.12.
  6. Secure the card. Replace the screw that held the slot cover on. This secures the card firmly in the slot. This is a step that network technicians frequently omit, but an important one, as a yank on the network cable can pull the card partially out of the slot, causing intermittent problems that are difficult todiagnose.
  7. Replace the computer case and secure it with the fasteners provided.

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

Configuring a network interface adapter is a matter of configuring it to use certain hardware resources, such as the following:

  • Interrupt requests (IRQs).  These are hardware lines that peripheral devices use to send signals to the system processor, requesting its attention.
  • Input/output (I/O) port addresses.  These locations in memory are assigned for use by particular devices to exchange information with the rest of the computer.
  • Memory addresses.  These areas of upper memory are used by particular devices, usually for installation of a special-purpose basic input/output system (BIOS).
  • Direct memory access (DMA) channels.  These are system pathways used by devices to transfer information to and from system memory.

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

Installing Network Interface Adapter Drivers

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.

Troubleshooting a Network Interface Adapter

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:

  • Make sure the network cable is firmly seated into the connector on the network interface adapter. If you're using a hub, check the cable connection there as well. Loose connections are a common cause of communications problems.
  • Try using a different cable that you know works. If you are using a permanently installed cable run, plug another properly working computer into it and use different patch cables. It is possible for the cable to be causing the problem, even if there is no visible fault.
  • Make sure that you have the proper driver installed on the computer. You might want to check the driver documentation and the network interface adapter manufacturer's Web site for information on possible driver problems on your operating system before you open up the computer.
  • Check to see that all of the other software components required for network communications, such as clients and protocols, are properly installed on the computer.

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.

Exercise 1: Network Adapter Functions

  1. The two hardware resources used by every network interface adapter are __________ and __________.
  2. Network interface adapters are associated with the protocol operating at the __________ layer.
  3. The network interface adapter packages data for transmission by enclosing it within a __________.

Lesson Review

  1. What is the name of the process of building a frame around network layerinformation?
    1. Data buffering
    2. Signal encoding
    3. MAC
    4. Data encapsulation
  2. Which of the connectors on a network interface adapter transmits data in parallel?
  3. Which of the following hardware resources do network interface adapters usually require? (Select two.)
    1. DMA channel
    2. I/O port address
    3. IRQ
    4. Memory address
  4. What is the name of the process by which a network interface adapter determines when it should transmit its data over the network?
  5. Which bus type is preferred for a NIC that will be connected to a Fast Ethernet network?

Lesson Summary

  • A network interface adapter—generally a network interface card—provides the link between a computer and the network medium.
  • The network interface adapter and its driver implement the data-link layer protocol on the computer.
  • Hardware resource configuration issues or device conflicts cause most network interface card installation problems.


Network+ Certification Training Kit
Self-Paced Training Kit Exam 70-642: Configuring Windows Server 2008 Network Infrastructure
ISBN: 0735651604
EAN: 2147483647
Year: 2001
Pages: 105

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