Lesson 4: The Network Interface Card

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Lesson 4: The Network Interface Card Network interface cards (NICs) provide the interface between cables, discussed in the previous lesson, and computers.

1 Lesson 4: The Network Interface Card Network interface cards (NICs) provide the interface between cables, discussed in the previous lesson, and computers. This lesson explores the many different types cards and how their performance affects a network. It also discusses the various connectors used to connect the cards to the cables. After this lesson, you will be able to: Describe the role the NIC in a network, including preparing, sending, and controlling data. Describe the configurable options for NICs. List the primary considerations for selecting a NIC. Describe at least two enhancements to NICs that will improve network performance. The Role the Network Interface Card Network interface cards, usually referred to as NICs, act as the physical interface or connection between the computer and the network cable. Figure 2.24 shows a NIC with a coaxial-cable connection. The cards are installed in an expansion slot in each computer and server on the network. After the NIC has been installed, the network cable is attached to the card's port to make the actual physical connection between the computer and the rest the network. Figure 2.24 A sample NIC The role the NIC is to: Prepare data from the computer for the network cable. Send the data to another computer. Control the flow data between the computer and the cabling system. Receive incoming data from the cable and translate it into bytes that can be understood by the computer's central processing unit (CPU). Preparing the Data Before data can be sent over the network, the NIC must change it from a form the computer can understand to a form that can travel over a network cable. Data moves through a computer along paths called buses. These are actually several data paths placed side by side. Because the paths are side by side (parallel), data can move along them in lateral groups instead in a single (serial) data stream. Older buses, such as those used in the original IBM personal computer, were known as 8-bit buses because they could move data 8 bits at a time. The IBM PC/AT computer used a 16-bit bus, which means it could move data 16 bits at a time.

Computers manufactured today use 32-bit buses. When data travels on a computer's bus, it is said to be traveling in parallel because the 32 bits are moving along side by side.

2 Computers manufactured today use 32-bit buses. When data travels on a computer's bus, it is said to be traveling in parallel because the 32 bits are moving along side by side. Think a 32-bit bus as a 32-lane highway with 32 cars moving side by side (moving in parallel), each carrying one bit data. On the network cable, however, data must travel in a single stream bits. When data travels on a network cable it is said to be traveling as a serial transmission because one bit follows another. In other words, the cable is a one-lane highway, and the data always travels in one direction. The computer is either sending or receiving data, but never both at the same time. The NIC takes data that is traveling in parallel as a group and restructures it so that it will flow through the 1-bit-serial path the network cable. Figure 2.25 shows a server converting parallel data to serial data on the network. This is accomplished through the translation the computer's digital signals into electrical or optical signals that can travel on the network's cables. The component responsible for this is the transceiver (transmitter/receiver). Figure 2.25 Parallel data stream converted to a serial data stream Network Address In addition to transforming data, the NIC also has to advertise its own location, or address, to the rest the network to distinguish it from all the other cards on the network. A committee the Institute Electrical and Electronics Engineers (IEEE) assigns blocks addresses to each NIC manufacturer. The manufacturers hardwire these addresses into chips on the card by a process known as "burning" the address into the card. With this process, each NIC and therefore each computer has a unique address on a network. The NIC also participates in several other functions in sequence as it takes data from the computer and gets it ready for the network cable: The computer and NIC must communicate in order to move data from the computer to the card. On cards that can utilize Direct Memory Access (DMA, defined later in this lesson), the computer assigns some its memory space to the NIC. The NIC signals the computer, requesting the computer's data. The computer's bus moves the data from the computer's memory to the NIC. Because data can ten move faster on the bus or the cable than the NIC can handle, the data is sent to the card's buffer, a reserved portion RAM. Here it is held temporarily during both the transmission and reception data.

Sending and Controlling Data Before the sending NIC actually sends data over the network, it carries on an electronic dialog with the receiving NIC so that both cards agree on the following: The

sent How much data each card can hold before it overflows The speed the data transmission If a newer, faster, more sophisticated NIC needs to communicate with an older, slower NIC, both need to find

3 Sending and Controlling Data Before the sending NIC actually sends data over the network, it carries on an electronic dialog with the receiving NIC so that both cards agree on the following: The maximum size the groups data to be sent The amount data to be sent before confirmation receipt is given The time intervals between sending data chunks The amount time to wait before confirmation is sent How much data each card can hold before it overflows The speed the data transmission If a newer, faster, more sophisticated NIC needs to communicate with an older, slower NIC, both need to find a common transmission speed that each can accommodate. Some newer NICs incorporate circuitry that allows the faster card to adjust to the rate the slower card. Each NIC signals to the other indicating its own parameters and accepting or adjusting to the other card's parameters. After all the communication details have been determined, the two cards begin to send and receive data. Configuration Options and Settings Network interface cards ten have configurable options that must be set in order for the card to function properly. Some the older designs use externally mounted dual inline package (DIP) switches as shown in Figure The following are examples configurable options: Interrupt (IRQ) Base input/output (I/O) port address Base memory address NOTE Many newer NICs use Plug and Play (PnP) technology; consequently, older cards that require setting options manually are becoming obsolete. (Plug and Play is discussed in more detail later in this lesson.) Figure 2.26 Older NIC with DIP switches Interrupt Request (IRQ) Lines Interrupt request lines (IRQs) are hardware lines over which devices such as I/O ports, the keyboard, disk drives, and NICs can send interrupts or requests for service to the computer's microprocessor. Interrupt request lines are built into the computer's internal hardware and are assigned different levels priority so that the microprocessor can determine the relative importance incoming service requests.

When the NIC sends a request to the computer, it uses an interrupt an electronic signal sent to the computer's CPU. Each device in the computer must use a different interrupt request line.

IRQ5 is the recommended setting if it is available, and it is the default for most systems. Use a system diagnostic tool to determine which IRQs are already being used.

4 When the NIC sends a request to the computer, it uses an interrupt an electronic signal sent to the computer's CPU. Each device in the computer must use a different interrupt request line. The interrupt line is specified when the device is configured. For examples, see image 2.5 that follows. In most cases, IRQ3 or IRQ5 can be used for the NIC, as we will see later in this chapter. IRQ5 is the recommended setting if it is available, and it is the default for most systems. Use a system diagnostic tool to determine which IRQs are already being used. If neither IRQ3 nor IRQ5 is available, refer to the following image for alternative values to use. The IRQs listed here as available usually can be used for a NIC. If the computer does not have the hardware device listed for a specific IRQ, that IRQ should be available for use. Image Standard IRQ Settings Base I/O Port The base I/O port specifies a channel through which information flows between the computer's hardware (such as the NIC) and its CPU. The port appears to the CPU as an address. Each hardware device in a system must have a different base I/O port number. The port numbers, in hexadecimal format (the system that uses 16 rather than 10 as the basis for its numbering) in the following table, are usually available to assign to a NIC unless they are already in use. Those with a device listed next to them are addresses commonly used for the devices. Check the computer documentation to determine which addresses are already in use. Table 2.6 Base I/O Port Settings Port Device Port Device 200 to 20F Game port 300 to 30F NIC 210 to 21F 310 to 31F NIC 220 to 22F 320 to 32F Hard-disk controller (for PS/2 Model 30) 230 to 23F Bus mouse 330 to 33F

Base Memory Address The base memory address identifies a location in a computer's memory (RAM). The NIC uses this location as a buffer area to store the incoming and outgoing data frames.

5 Base Memory Address The base memory address identifies a location in a computer's memory (RAM). The NIC uses this location as a buffer area to store the incoming and outgoing data frames. This setting is sometimes called the RAM start address. NOTE NICs that do not use system RAM do not have a setting for the base memory address. Some NICs contain a setting that allows you to specify the amount memory to be set aside for storing data frames. For example, for some cards you can specify either 16 KB or 32 KB memory. Specifying more memory provides better network performance but leaves less memory available for other uses. NIC, Bus, and Cable Compatibility To ensure compatibility between the computer and the network, the NIC must: Fit with the computer's internal structure (data bus architecture). Have the right type cable connector for the cabling. For example, a card that would work in an Apple computer communicating in a bus network will not work in an IBM computer in a ring environment: The IBM ring requires cards that are physically different from those used in a bus; and Apple uses a different network communication method. Data Bus Architecture In the personal computer environment, there are four types computer bus architectures: ISA, EISA, Micro Channel, and PCI. Each type bus is physically different from the others. It is essential that the NIC and the bus match. Figure 2.28 shows examples each type computer bus. Industry Standard Architecture (ISA) Extended Industry Standard Architecture (EISA) Micro Channel Architecture Peripheral Component Interconnect (PCI) Figure 2.28 ISA, EISA, Micro Channel, and PCI network interface cards

Network Cabling and Connectors The network interface card performs three important functions in coordinating activities between the computer and the cabling: it Makes the physical connection to the

To select the appropriate NIC for your network, you first need to determine the type cabling and cabling connectors it will have.

6 Network Cabling and Connectors The network interface card performs three important functions in coordinating activities between the computer and the cabling: it Makes the physical connection to the cable. Generates the electrical signals that travel over the cable. Controls access to the cable by following specific rules. To select the appropriate NIC for your network, you first need to determine the type cabling and cabling connectors it will have. As discussed in the previous lesson, each type cable has different physical characteristics that the NIC must accommodate. Each card is built to accept at least one type cable. Coaxial, twisted-pair, and fiber-optic are the most common cable types. Some NICs have more than one interface connector. For example, it is not uncommon for a NIC to have a thinnet, thicknet, and twisted-pair connector. If a card has more than one interface connector and does not have built-in interface detection, you should make a selection by setting jumpers on the card itself or by using a stware-selectable option. Consult the NIC documentation for information on how to properly configure the card. Three examples typical connectors found on NICs are shown in the following three illustrations. A thinnet network connection uses a coaxial BNC connector as shown in Figure Figure 2.29 Thinnet network connection for a coaxial BNC connector A thicknet network connection uses a 15-pin attachment unit interface (AUI) cable to connect the 15-pin (DB-15) connector on the back the NIC to an external transceiver. As discussed earlier in Lesson 1, the external transceiver uses a vampire tap to connect to the thicknet cable. Figure 2.30 shows a 15-pin AUI connection. Figure 2.30 Thicknet network connection for a 15-pin AUI

IMPORTANT Be careful not to confuse a joystick port with an AUI external transceiver port; they look alike, but some joystick pins carry 5 volts DC, which can be harmful to network hardware as well

7 IMPORTANT Be careful not to confuse a joystick port with an AUI external transceiver port; they look alike, but some joystick pins carry 5 volts DC, which can be harmful to network hardware as well as to the computer. You need to be familiar with the specific hardware configuration in order to determine whether the connector is for a NIC or a joystick. Similarly, be careful not to confuse 25-pin SCSI ports with parallel printer ports. Some older SCSI devices communicated through the same kind DB-25 connector as these parallel ports, but neither device will function when plugged into the wrong connector. An unshielded twisted-pair connection uses a RJ-45 connector, as shown in Figure The RJ-45 connector is similar to a RJ-11 telephone connector but is larger in size and has eight conductors; a RJ-11 only has 4 conductors. Figure 2.31 RJ-45 connector Network Performance Because the effect it has on data transmission, the NIC has a significant effect on the performance the entire network. If the card is slow, data will not pass to and from the network quickly. On a bus network, where no one can use the network until the cable is clear, a slow card can increase wait times for all users. After identifying the physical requirements the NIC the computer bus, the type connector the card needs, and the type network in which it will operate it is necessary to consider several other factors that affect the capabilities the card. Although all NICs conform to certain minimum standards and specifications, some cards feature enhancements that greatly improve server, client, and overall network performance. You can speed up the movement data through the card by adding the following enhancements: Direct memory access (DMA) With this method, the computer moves data directly from the NIC's buffer to the computer's memory, without using the computer's microprocessor. Shared adapter memory In this method, the NIC contains RAM that it shares with the computer. The computer identifies this RAM as if it is actually installed in the computer. Shared system memory In this system, the NIC's processor selects a section the computer's memory and uses it to process data. Bus mastering With bus mastering, the NIC takes temporary control the computer's bus, bypasses the computer's CPU, and moves data directly to the computer's system memory. This speeds up computer operations by freeing the computer's processor to deal with other tasks. Bus mastering cards can be expensive, but they can improve network performance by 20 to 70 percent. EISA, Micro Channel, and PCI network interface cards fer bus mastering.

8 RAM buffering Network traffic ten travels too fast for most NICs to handle. RAM chips on the NIC serve as a buffer. When the card receives more data than it can process immediately, the RAM buffer holds some the data until the NIC can process it. This speeds up the card's performance and helps keep the card from becoming a bottleneck. On-board microprocessor With a microprocessor, the NIC does not need the computer to help process data. Most cards feature their own processors that speed network operations. Servers Because they handle such high volumes network traffic, servers should be equipped with the highest-performance cards possible. Workstations Workstations can use less expensive NICs if their main network activities are limited to applications, such as word processing, that do not generate high volumes network traffic. Recall, though, that on a bus network, a slow NIC can increase wait times for all users. Other applications, such as those databases or engineering, will quickly overwhelm inadequate NICs. Specialized NICs So far, this lesson has focused on standard network interface cards. In the majority situations, you will be using one these cards to connect each computer to the physical network. In reality, some situations will require the use specialized network connections and therefore require specialized network cards. The remainder this lesson introduces you to three varieties these specialized cards. Wireless NICs Some environments require an alternative to cabled computer networking. Wireless NICs are available that support the major network operating systems. Wireless NICs ten come with many features. These include: Indoor omnidirectional antenna and antenna cable. Network stware to make the NIC work with a particular network. Diagnostic stware for troubleshooting. Installation stware. These NICs can be used to create an all-wireless LAN or to add wireless stations to a cabled LAN. Usually, these NICs are used to communicate with a component called a wireless concentrator that acts as a transceiver to send and receive signals. NOTE A concentrator is a communications device that combines signals from multiple sources, such as terminals on a network, into one or more signals before sending them to their destination.

9 Fiber-Optic NICs "Fiber to the desktop" has become a catchphrase for the computing industry. As transmission speeds increase to accommodate the bandwidth-hungry applications and multimedia data streams that are common on today's intranets, fiberoptic network cards allow direct connections to high-speed fiber-optic networks. These cards have recently become costcompetitive, and it's expected that their use will someday be commonplace. Lesson Summary The following points summarize the main elements this lesson: Network interface cards (NICs) are computer expansion cards that provide the interface between the network cabling and the computer. The function the NIC is to prepare, send, receive, and in a Ring topology retransmit data on the network. A NIC is installed just like any other expansion card. You must properly set the IRQ, the base I/O port address, and the base memory address. In order for a NIC to be physically installed in the computer and connected to the network, it must both match the computer's expansion bus type and have the proper connector fittings for the network cabling. A network's performance is only as good as its weakest link. Many aspects a NIC can either enhance or restrict the performance the network. Be careful when selecting an economical card; it just might become the limiting factor in your network's performance.

Darshan Institute of Engineering & Technology for Diploma Studies

Darshan Institute of Engineering & Technology for Diploma Studies 1. Explain different network devices in detail. Or Explain NIC (Network Interface Card) in detail. Network interface cards are add on cards as hardware cards on the motherboard. This is additional hardware