Networking.docx

Identifying Common Network Hardware We have looked at the types of networks, network topologies, and the way communications are handled. That’s all of the logical stuff. To really get computers to talk to each other requires hardware. Every computer on the network needs to have a network adapter of...

Identifying Common Network Hardware We have looked at the types of networks, network topologies, and the way communications are handled. That’s all of the logical stuff. To really get computers to talk to each other requires hardware. Every computer on the network needs to have a network adapter of some type. In many cases, you also need some sort of cable to hook them together. (Wireless networking is the exception, but at the backend of a wireless network there are still components wired together.) And finally, you might also need connectivity devices to attach several computers or networks to each other. Network Interface Cards The network interface card (NIC), also referred to as a network adapter card, provides the physical interface between computer and cabling. It prepares data, sends data, and controls the flow of data. It can also receive and translate data into bytes for the CPU to understand. NICs come in many shapes and sizes. Different NICs are distinguished by the PC bus type and the network for which they are used. The following sections describe the role of NICs and how to evaluate them. Compatibility The first thing you need to determine is whether the NIC will fit the bus type of your PC. If you have more than one type of bus in your PC (for example, a combination PCI/PCI Express), use a NIC that fits into the fastest type (the PCI Express, in this case). This is especially important in servers because the NIC can quickly become a bottleneck if this guideline isn’t followed. More and more computers are using NICs that have USB interfaces. For the rare laptop computer that doesn’t otherwise have a NIC built into it, these small portable cards are very handy.  A USB network card can also be handy for troubleshooting. If a laptop isn’t connecting to the network properly with its built-in card, you may be able to use the USB NIC to see if it’s an issue with the card or perhaps a software problem. Network Interface Card Performance The most important goal of the NIC is to optimize network performance and minimize the amount of time needed to transfer data packets across the network. The key is to ensure that you get the fastest card that you can for the type of network that you’re on. For example, if your wireless network supports 802.11g/n/ac, make sure to get an 802.11ac card because it’s the fastest. 334 Sending and Controlling Data In order for two computers to send and receive data, the cards must agree on several things: The maximum size of the data frames The amount of data sent before giving confirmation The time needed between transmissions The amount of time to wait before sending confirmation The speed at which data transmits If the cards can agree, the data is sent successfully. If the cards cannot agree, the data is not sent. To send data on the network successfully, all NICs need to use the same media access method (such as CSMA/CD) and be connected to the same piece of cable. This usually isn’t a problem, because the vast majority of network cards sold today are Ethernet. In addition, NICs can send data using either full-duplex or half-duplex mode. Half-duplex communication means that between the sender and receiver, only one of them can transmit at any one time. In full-duplex communication, a computer can send and receive data simultaneously. The main advantage of full-duplex over half-duplex communication is performance. NICs (Gigabit Ethernet NICs) can operate twice as fast (1 Gbps) in full-duplex mode as they do normally in half-duplex mode (500 Mbps). In addition, collisions are avoided, which speeds up performance as well. Configuring the network adapter’s duplexing setting is done from the Advanced tab of the NIC’s properties, as shown in Figure 6.12. Figure 6.12 A NIC’s Speed & Duplex setting 335  Normally, you aren’t going to have to worry about how your NIC sends or controls data. Just make sure to get the fastest NIC that is compatible with your network. Do know that the negotiations discussed here are happening in the background, though. NIC Configuration Each card must have a unique hardware address, called a Media Access Control address or MAC address. If two NICs on the same network have the same hardware address, neither one will be able to communicate. For this reason, the IEEE has established a standard for hardware addresses and assigns blocks of these addresses to NIC manufacturers, who then hard-wire the addresses into the cards. MAC addresses are 48 bits long and written in hexadecimal, such as B6-15-53-8F-29-6B. An example is shown in Figure 6.13 from the output of the ipconfig /all command executed at the command prompt. Figure 6.13 Physical (MAC) address  Although it is possible for NIC manufacturers to produce multiple NICs with the same MAC address, it happens very rarely. If you do encounter this type of problem, contact the hardware manufacturer. 336 NIC Drivers In order for the computer to use the NIC, it is very important to install the proper device drivers. These drivers are pieces of software that communicate directly with the operating system, specifically the network redirector and adapter interface. Drivers are specific to each NIC and operating system, and they operate in the Media Access Control (MAC) sublayer of the Data Link layer of the OSI model. To see which version the driver is, you need to look at the device’s properties. There are several ways to do this. A common one is to open Device Manager (click Start, type Device, and click Device Manager under Best match), and find the device, as shown in Figure 6.14. Figure 6.14 Device Manager Right-click the device, click Properties, and then go to the Driver tab, as shown in Figure 6.15. Here you can see a lot of information about the driver, update it, or roll it back if you installed a new one and it fails for some reason. You can also update the driver by right-clicking the device in Device Manager and choosing Update driver from the popup menu. Figure 6.15 NIC properties Driver tab 337  The best place to get drivers is always the manufacturer’s website. When you click Update Driver, Windows will ask you if you want to search for the driver on the Internet or provide a location for it. The best course of action is to download the driver first, and then tell Windows where you put it. Cables and Connectors When the data is passing through the OSI model and reaches the Physical layer, it must find its way onto the medium that is used to transfer data physically from computer to computer. This medium is called the cable (or in the case of wireless networks, the air). It is the NIC’s role to prepare the data for transmission, but it is the cable’s role to move the data properly to its intended destination. The following sections discuss the three main types of physical cabling: coaxial, twisted-pair, and fiber-optic. (Wireless communication is covered in Chapter 8.) 338 Coaxial Cable Coaxial cable (or coax) contains a center conductor core made of copper, which is surrounded by a plastic jacket with a braided shield over it (as shown in Figure 6.16). Either Teflon or a plastic coating covers this metal shield. Figure 6.16 Coaxial cable Common network cables are covered with a plastic called polyvinyl chloride (PVC). While PVC is flexible, fairly durable, and inexpensive, it has a nasty side effect in that it produces poisonous gas when burned. An alternative is a Teflon-type covering that is frequently referred to as a plenum-rated coating. That simply means that the coating does not produce toxic gas when burned and is rated for use in the ventilation plenum areas in a building that circulate breathable air, such as air conditioning and heating systems. This type of cable is more expensive, but it may be mandated by electrical code whenever cable is hidden in walls or ceilings.  Plenum rating can apply to all types of network cabling. Coax Cable Specifications Coaxial cable is available in various specifications that are rated according to the Radio Guide (RG) system, which was originally developed by the US military. The thicker the copper, the farther a signal can travel—and with that comes a higher cost and a less- flexible cable. When coax cable was popular for networking, there were two standards that had fairly high use: RG-8 (thicknet) and RG-58A/U (thinnet). Thicknet had a maximum segment distance of 500 meters and was used primarily for network backbones. Thinnet was more often used in a conventional physical bus. A thinnet segment could span 185 meters. Both thicknet and thinnet had impedance of 50 ohms. Table 6.2 shows the different types of RG cabling and their uses. The ones that are included on the A+ exam objectives are RG-6 and RG-59. 339 Table 6.2 Coax RG types RG # Popular Name Ethernet Implementation Type of Cable RG-6 Satellite/cable TV, cable modems N/A Solid copper RG-8 Thicknet 10Base5 Solid copper RG-58 U N/A None Solid copper RG-58 A/U Thinnet 10Base2 Stranded copper RG-59 Cable television N/A Solid copper Explaining Ethernet Naming Standards In Table 6.2, you will notice two terms that might be new to you: 10Base5 and 10Base2. These are Ethernet naming standards. The number at the beginning tells you the maximum speed that the standard supports, which is 10 Mbps in this case. The word Base refers to the type of transmission, either baseband (one signal at a time per cable) or broadband (multiple signals at the same time on one cable). Legend has it that the 5 and the 2 refer to the approximate maximum transmission distance (in hundreds of meters) for each specification. Later in the chapter, you will see 10BaseT, which refers to twisted-pair cabling. Coaxial networking has all but gone the way of the dinosaur. The only two coaxial cable types used today are RG-6 and RG-59. Of the two, RG-6 has a thicker core (1.0 mm), can run longer distances (up to 304 meters, or 1000 feet), and support digital signals. RG-59 (0.762 mm core) is considered adequate for analog cable TV but not digital and has a maximum distance of about 228 meters (750 feet). The maximum speed for each depends on the quality of the cable and the standard on which it’s being used. Both have impedance of 75 ohms. Coax Connector Types Thicknet was a bear to use. Not only was it highly inflexible, but you also needed to use a connector called a vampire tap. A vampire tap is so named because a metal tooth sinks into the cable, thus making the connection with the inner conductor. The tap is connected to an external transceiver that in turn has a 15-pin AUI connector (also called a DIX or DB-15 connector) to which you attach a cable that connects to the station. The transceiver is shown in Figure 6.17. On the right side, you will see the thicknet cable running through the portion of the unit that contains the vampire tap. DIX got its name from the companies that worked on this format—Digital, Intel, and Xerox. 340 Figure 6.17 Thicknet transceiver and cable inside a vampire tap   Thicknet transceiver licensed Under CC BY-Sa 2.5 via Wikimedia Commons. http://commons.wikimedia.org/wiki/File:ThicknetTransceiver.jpg#/media/File:ThicknetTransceiver.jpg Thinnet coax was much easier to use. Generally, thinnet cables used a BNC connector (see Figure 6.18) to attach to a T-shaped connector that attached to the workstation. The other side of the T-connector would either continue on with another thinnet segment or be capped off with a terminator. It is beyond the scope of this book to settle the long-standing argument over the meaning of the abbreviation BNC. We have heard Bayonet Connector, Bayonet Nut Connector, and British Naval Connector—among others. What is relevant is that the BNC connector locks securely with a quarter-twist motion. Figure 6.18 Male and female BNC connectors, T-connector, and terminator 341 Another type of connector that you will see in use with coax is a splitter. As its name implies, a splitter takes a single signal (say that three times fast) and splits it into multiple replicas of the same signal. You might use this for cable TV—one line may run into your house, but the signal ultimately needs to get split for three televisions. This type of configuration will work for cable TV or cable Internet. Figure 6.19 shows a one-to-two coax splitter. You can also buy splitters that split one input into three or more outputs. Figure 6.19 A coax splitter Keep in mind that a coax signal is designed to go from one sender to one receiver, so splitting it can cause some issues. Splitting the signal causes it to weaken, meaning that signal quality could be lower, and it might not travel the same distance as a non-split signal. To avoid problems, don’t over-split the cable, and purchase a good quality or amplified splitter. The last type of coax connector we will cover is called an F-connector (shown in Figure 6.20), and it is used with cable TV. The exposed end of the copper cable is pushed into the receptacle, and the connector is threaded so that it can screw into place. Figure 6.20 An F-connector 342 Twisted-Pair Cable Twisted-pair is the most popular type of cabling to use because of its flexibility and low cost. It consists of several pairs of wire twisted around each other within an insulated jacket, as shown in Figure 6.21. Figure 6.21 Unshielded twisted-pair cable There are two different types of twisted-pair cables: shielded twisted-pair (STP) and unshielded twisted-pair (UTP). Both types of cable have two or four pairs of twisted wires going through them. The difference is that STP has an extra layer of braided foil shielding surrounding the wires to decrease electrical interference, as shown in Figure 6.22. (In Figure 6.22, the individual wire pairs are shielded as well.) UTP has a PVC or plenum coating but no outer foil shield to protect it from interference. In the real world, UTP is the most common networking cable type used, whereas STP is used infrequently. Figure 6.22 Shielded twisted-pair cable 343  You will often hear people refer to UTP cables as Ethernet cables. As you learned earlier in this chapter, Ethernet is an access method based on the IEEE 802.3 standard and not related to a specific cable type. So while technically it’s incorrect, there’s no harm in using the term to refer to the cable. Twisted-Pair Cable Specifications There aren’t any STP standards that you really need to know about, either for the test or real-life situations. UTP is a different animal. It comes in several grades to offer different levels of performance and protection against electrical interference: Category 1 contains two twisted pairs. It is for voice-only transmissions, and it is in many legacy phone systems today. Category 2 is the lowest-grade cable that can have four pairs of wires. (Every other CAT rating since CAT-2 has four pairs.) It can handle data transmission at speeds up to 4 Mbps. Category 3 is able to transmit data at speeds up to 10 Mbps. It was popular for 10BaseT installations before CAT-5 came out. Category 4 is able to transmit data at speeds up to 16 Mbps. Category 5 is able to transmit data at speeds up to 100 Mbps. Category 5e is able to transmit data at speeds up to 1 Gbps. The enhancement over CAT-5 is that the four twisted pairs of copper wire are physically separated and contain more twists per foot. This provides maximum interference protection. Category 6 is able to transmit data at speeds up to 10 Gbps, but only up to a distance of 55 meters. Its four twisted pairs of copper wire are oriented differently than in CAT-5e. This is the lowest grade of cable you should ever use as a backbone to connect different parts of a network together, such as those on different floors of a building. Category 6a can also handle 10 Gbps speed, but at longer distances (up to 100 meters) than CAT-6 can. Category 7 is an incremental upgrade over CAT-6e. Its most notable feature is that every wire pair is shielded, which provides better resistance to crosstalk and external noise. It can handle 10 Gbps at up to 100 meters. You might hear it also called Class F cabling.  CompTIA (and many others) usually shortens the word category to CAT and use the form CAT-5 to refer to Category 5, for example. This is a common way to refer to these categories, and you can feel free to use these terms interchangeably. If you are buying cable today, you shouldn’t buy anything older than CAT-5e. 344  Before the CAT-6a standard was finalized, several cable vendors started selling CAT-6e cable. Much like CAT-5e was an enhanced version of CAT-5, CAT-6e was supposed to be an enhanced version of CAT-6. The thing is, an official CAT-6e specification was never officially established; if you buy CAT-6e, there is no guarantee of the type of performance that you will get. The official standard is CAT-6a. The standard maximum transmission distance for UTP is 100 meters (328 feet). Note, however, that if you want to run 10GBaseT over CAT-6, you won’t get that much distance—about 55 meters under ideal conditions. Twisted-Pair Connector Types Twisted-pair cabling uses a connector type called an RJ (registered jack) connector. You are probably familiar with RJ connectors. Most landline phones connect with an RJ-11 connector. The connector used with UTP cable is called RJ-45. The RJ-11 has room for two pairs (four wires), and the RJ-45 has room for four pairs (eight wires). In almost every case, UTP uses RJ connectors; a crimper is used to attach an RJ connector to a cable. Higher-quality crimping tools have interchangeable dies for both types of connectors. (Crimpers are discussed in Chapter 14, “Hardware and Network Troubleshooting.”) Figure 6.23 shows an RJ-11 connector and an RJ-45 connector. Figure 6.23 RJ-11 and RJ-45 connectors You will also find RJ-45 splitters (often called Ethernet splitters) in the marketplace. The idea is similar to a coax splitter, but functionally they are very different. Coax signals are carried over one wire, while twisted pair uses either two pairs of wires (for 100 Mbps or slower connections) or all four pairs of wires (for Gigabit Ethernet and faster). An Ethernet splitter will take the incoming signal on two pairs and then split it, so on the output end345it produces two sets of signals using two pairs each. Because of this, Ethernet splitters are limited to 100 Mbps connections.  It is not recommended that you use Ethernet splitters on a network. If you need to connect multiple computers together using UTP, use a hub or a switch. We talk about both of these devices later in this chapter.