Chapter 7. Network Interface Cards
SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE
The network interface card ( NIC ) is the piece of hardware that links a computer or workstation to the network media. The standard Ethernet NIC resides at the Physical level of the OSI Seven-Layer Reference Model and is the device responsible for translating data into zeros and ones for transmission on the network media for the network using electricity or light. To send data to and from other computers, the NIC's driver software interfaces with the NIC's hardware elements and with the protocol stack that runs on the computer.
Although this chapter concentrates
Virtually all cards manufactured today support Plug and Play (PnP), although some older operating systems do notthat would make life too simple. So, although you might find that installing a new workstation or upgrading an old one with a new network adapter card is an easy task, this might not always be the case if you are working on older equipment. In this chapter, we'll look at the differences between card types and the items that are typically configurable for NICs. After that, we'll list some of the methods you can use to troubleshoot network problems when you suspect that the NIC might be the problem.
Choosing a Hardware Bus Type
When you install a card in a workstation or server, whether it is a network adapter card or a SCSI disk adapter card, you insert the card into a slot that connects the card to a bus . A bus is nothing more than a communications channel that devices can use to exchange information with the computer's CPU and memory.
Different kinds of cards can be inserted into slots to connect them to the bus in the computer. Before you make a decision on what kind of network card to purchase, you need to know what kinds of bus slots are available on the computer and which are available for use. For example, all major computer manufacturers today use the Peripheral Component Interconnect (PCI) bus (or a
While it will eventually be phased out in favor of PCI Express, another slot you're likely to find in most systems is the Accelerated Graphics Port (AGP). You can usually distinguish this slot from other types of slots by its pin-outonly an AGP card fits into the slotand its
The FireWire (IEEE 1394) bus, which Windows XP recognizes as a network adapter, is another competitor that offers bandwidth comparable to USB 2.0 and
PCI cards for both FireWire and USB can be purchased inexpensively if your computer does not come with them. As you read this chapter, keep in mind (1) the number of available slots you can use in an ISA/EISA bus or PCI bus, and (2) the number of devices you will use the USB or FireWire bus for. If your workstations are all newer models, you will find that only slots based on PCI technologies (PCI, PCI-X and PCI-Express) are available. About the only new PCs that use EISA or ISA slots are those which
In addition to the bus types discussed in this chapter, you might occasionally hear about the MCA bus. MCA stands for Micro Channel Architecture. This bus was a proprietary standard that IBM created in 1987. Although MCA was, in most respects, superior to the other bus specifications at that time , it is not compatible with other buses. Because incorporating MCA technology required licensing it from IBM, card manufacturers never widely adopted MCA. Instead, the EISA specification was developed partly in response to the proprietary nature of MCA. Both MCA and EISA have been obsolete for several years.
Another network adapter that has just recently become an inexpensive solution for networking computers is the wireless network adapter, of which there are several types. The portability that wireless networking enables is one of its best features. There are some considerations, such as security, that are being addressed with newer standards. Wireless networks are discussed extensively in Part V, "Wireless Networking Protocols."
In this discussion we'll start with the older technologies (some of which are still widely used) and then go on to discuss newer network adapter cards.
The ISA (Industry Standard Architecture) bus was created in the 1980s and was the bus used by the first IBM personal computer architecture. Manufacturers adopted the
The first version of this bus provided for an 8-bit data channel. The IBM AT computer architecture used an enhanced version of the original ISA bus, allowing for data transfers at a rate of 8MHz, using a 16-bit data channel. This architecture was later expanded on, and the Extended ISA (EISA) bus was created. Although the EISA bus still operates at only 8MHz, it allows for a 32-bit
Figure 7.1. The network interface card on the left has an ISA interface, whereas the one on the right is designed for use in a PCI slot.
As mentioned earlier in this chapter, most newer PCsparticularly those built since 2000are
The PCI bus specifications have many advantages over previous standards, including dramatically faster data transfer rates and 32-or 64-bit-wide data paths. Devices on the PCI bus can also use a feature called bus mastering , whereby a card can take control of the bus and directly transfer large amounts of data to system memory without using the CPU. PCI has made the ISA/EISA buses obsolete.
Besides its performance advantage over the EISA bus, the PCI bus also allows for
Other information contained in the PCI card's registers
An IRQ is a hardware component of the computer that devices can use to send an
signal to the CPU in an attempt to get the attention of the processor. For example, when a network adapter needs to transfer data from its buffer into the computer's memory, it will use the IRQ assigned to it to notify the CPU that a request is pending. Using the IRQ line does not guarantee that the device will get an immediate response from the CPU, however. The CPU might be executing instructions that cannot be
Usually the PCI card is configured to use an available IRQ when the system detects it. If an unused IRQ isn't found, the card can, under some circumstances, share an IRQ with another card. In that case, the system interrogates each card that shares the IRQ when the CPU receives the interrupt request. The card making the request can then communicate with the CPU to
The PCI bus also has several variants, such as the Mini PCI, CompactPCI, Low-Profile PCI, Concurrent PCI, PCI-X, and PCI-Express specifications, each of which is used to create a PCI-compliant bus in different computer configurations. For example, the Mini PCI bus is generally used in laptop or smaller computing devices. This PCI bus is implemented as a card that you can install in one of these smaller computer devices to enable connections to other peripheral devices, such as modems and (the topic of this chapter) network adapter cards.
Table 7.1 provides a useful overview of the different PCI bus types.
Table 7.1. PCI Bus Types
Although PCI slots are used in most desktop and server computers for holding adapter cards, smaller computers, such as laptops, are another matter altogether. Because of their
PCMCIA cards (or PC Cards if you prefer) are credit-cardsize cards that can be used in laptops and other small computers. The acronym does
stand for "People Can't Memorize Computer Industry Acronyms," which is a popular phrase used to remember the acronym. Instead, PCMCIA is the Personal Computer Memory Card International Association, which is a
Figure 7.2. PC Cards and CardBus cards (shown here) are much smaller than standard network adapter cards.
You can use the URL
to find more information about PCMCIA cards. This trade organization has been around for many years and has been responsible for many developments in this small form factor card for use in laptop computers and, more recently, consumer devices such as digital
In 1996, the PCMCIA organization developed the CardBus for use in small computing devices, such as laptop computers. This standard provides a 32-bit data path, which can enable PC Card devices to
So, which kind of card should you choose for your networking needs? That can depend on many factors. For example, you might be limited on the kind of card by how many slots are available in the computers, and of what type. Note that if you have run out of slots for a network adapter, but have USB 2.0 ports in the system, you can plug an Ethernet adapter into a USB 2.0 port. Because USB 2.0 (also known as Hi-Speed USB) runs at 480Mbps, and Fast Ethernet runs at 100Mbps, you will not create a bottleneck for your network connection by using a USB network adapter.
If you want to get a greater understanding of how the types of buses discussed in this chapter work, I recommend that you check out Upgrading and Repairing PCs , by Scott Mueller, which also is published by Que. Visit www.upgradingandrepairingpcs.com to learn more about this industry classic.
Some large server installations don't use network adapter cards. Instead, they use a technology called InfiniBand. InfiniBand was developed to solve many problems associated with I/O between the computer's CPU/memory and external devices. By using fiber optics and a switched network, InfiniBand greatly extends the connectivity between the CPU, memory, and other
Different Cards, Different Speeds
Another factor to consider when making a network card purchase is the speed of your network. Standard 10BASE-T networks operate at 10Mbps. If you are upgrading, it is more likely that you'll be using or upgrading to at least a 100Mbps network. If so, you'll probably be upgrading the backbone cabling that connects your switches/routers also to a higher bandwidth, such as Gigabit Ethernet.
If you are creating a new network, simply choose 100Mbps cards. If you are upgrading an existing network, and if the cabling infrastructure supports 100Mbps, you can slowly migrate users to 100Mbps by purchasing cards that operate at both speeds. Virtually all current 10/100Mbps cards also support
, which means that they can detect the speed of the network connection and adjust
Network Cable Connectors and Terminators
In Chapter 6, "Wiring the NetworkCables, Connectors, Concentrators, and Other Network Components," the various kinds of network cables and connectors that can be used to create a LAN were examined. Although most older 10BASE-2 networks have already been upgraded to 10BASE-T (or faster) networks, there are still a few around that use thinnet coaxial cable with BNC connectors and terminators. If the computers on a thinnet network use "combo cards" (see Figure 7.3), you can upgrade to UTP cable without changing network adapters. These cards let you either connect a BNC T-connector to the card or use an RJ-45 jack for the newer 10BASE-T networks. However, I suspect that this will be a rare situation. If you are still operating with coaxial cables in your Ethernet network, you need to immediately
Figure 7.3. A combo card contains both a BNC and an RJ-45 receptacle and can be used on both types of networks.