CHAPTER 2: Network Media 86 IEEE1394 (FireWire) If you’ve ever hooked up a digital camera, digital video (DV) camera, or other devices that need to transfer large amounts of data to your computer, you may have used FireWire. FireWire is a proprietary name for an external bus that supports fast data transfer rates. Apple Computers originally developed the technology, but it has since been standardized as IEEE1394. Since then, other companies have developed their own trademark names, including Sony’s iLink. Devices that follow IEEE1394 allow data to be transferred at 400 Mbps (in IEEE1394a) and 800 Mbps (in IEEE1394b). In addition to this, it allows a single 1394 port to have up to 63 external devices connected to it. It is similar to USB in that can provide power to a device and supports both plug and play and hot plugging. Wireless Media As we discussed briefly in the previous chapter and will discuss in greater detail in Chapter 4, wireless networks require minimal cabling. Data is transmitted over the air using wireless adapters and wireless routers, so little to no cabling is required for network communication. Transceivers (Media Converters) The term transceiver is short for transmitter-receiver, which also describes its purpose on a network. Transceivers are the portion of a network interface that transmits and receives electrical signals across the transmission media. They are also the part of the interface that actually connects to the media. Transceiver types can be classified as being either on-board, which are built onto a network card, or external. With an external transceiver, the actual media connection is made external to the NIC using a small device that attaches via an extension cable to the NIC. The types of transceivers and media that can be served by a NIC determine the appropriate connector, and, as we saw earlier in this chapter, each media type has a typical connector type or connection method. One such connector is an AUI connector, which is also called a DIX connector. This type of connector can be found on the back of many NICs. The AUI connector enables a network card to be used with multiple types of media. A common implementation is to use this configuration for an Ethernet card that can be attached to twisted-pair, thickwire, or thinwire coax by just changing the external transceiver type. Summary of Exam Objectives 87 On networks that used 10Base2 and 10Base5 media, transceivers are used to connect to the cable and communicate with the network. 10Base5 networks use a device called a MAU, which taps into the thick cable and allows the workstation to connect to the network using an AUI cable. When a MAU and AUI cable are used on a 10Base5 network, the onboard trans- ceiver of the network card isn’t used. Instead, the transceiver in the MAU is used, which acquires power through the AUI cable from the network adapter card on the workstation. On 10Base2 networks, no more than 30 transceiv- ers can be connected to any segment, while on 10Base5 networks no more than 100 taps can be performed per segment. Because the network adapter’s transceiver isn’t used, the MAU detects collisions by sending out a signal called a heartbeat or signal quality error (SQE) test signal. The MAU’s heartbeat is sent to the workstation when a collision is detected, allowing it to deal with the collision accordingly, as we discussed in the previous chapter when discussing bus topologies. When a frame of data is successfully transmitted, the MAU will also send a heartbeat to determine whether the bus is active. An exception to performing this test is when a repeater is used on the net- work, which resends data to other segments of the network. When a repeater receives the heartbeat signal, it will identify it as a collision, and send a jam signal. To prevent this, and thereby keep the network from becoming bogged down with these signals, the MAU’s SQE test signal feature should be turned off if a repeater is used. SUMMARY OF EXAM OBJECTIVES Cabling and connectors are essential to any network, providing a medium that allows computers to communicate and send data across the network. Cabling can be twisted-pair, coaxial, or fiber optic. Coaxial consists of a single copper wire to carry data, twisted-pair uses pairs of copper wires twisted together, and fiber-optic cabling sends data across the network in the form of modulated pulses of light. In using the various cables, there are a number of issues that may impact the performance of a network. EMI can be caused by florescent lighting, machin- ery, or other sources that put out a low voltage, low current, high- frequency signal that can interfere electronic signals transmitted over cabling. Similar to this is RFI, which is caused by electromagnetic radiation in the radio fre- quency range. Putting cables too close to one another can cause another form of interference called crosstalk, where the electromagnetic field of one wire CHAPTER 2: Network Media 88 interferes with the transmission of another. Finally, data can weaken over distances, causing a problem called attenuation. These issues must be dealt with during the installation of network cable, or dealt with once cabling has been installed. When problems present themselves, electronic devices called cable tes- ters may be used to find the cause or location of a problem on the cable. Tools like tone generators, TDRs, wire map testers, and oscilloscopes can all provide information that is useful in fixing a problem. We also saw that data can travel along a cable in several ways, using a simplex, half-duplex, or full duplex data transfer. When simplex is used, data moves in a single direction. Half-duplex allows data to move in either direc- tion, but in only one direction at a time. When full duplex is used, however, data can move in either direction simultaneously. We discussed that Ethernet is a standard that’s used on most networks today. Ethernet has specifications for 10Base2, 10Base5, and 10BaseT networks, and uses CSMA/CD, which prevents devices from interfering with one another during transmission by detecting collisions of data. A newer variation of Ethernet is Fast Ethernet, which supports transfer speeds of up to 100 Mbps. There is a wide variety of media standards, some of which have been around since the early days of networking. 10Base2 and 10Base5 are net- works that use coaxial cable to transfer data, while 10BaseT, 100BaseTX, and 1000BaseT use UTP cabling. Finally, we also discussed various standards used for fiber-optic networks, including 10BaseFL, 100BaseFX, 100BaseSX, 1000BaseLX, and 1000BaseCX. Connectors are used to terminate cables and provide a method of con- necting the cable to the device. There are a number of connectors available, including D, RJ, DIX, and BNC for coaxial and twisted-pair networks. SC, ST, LC, and MTRJ connectors are used for fiber-optic cabling. Just as there are various connectors, there are also a variety of media types. Twisted-pair cable comes in a variety of grades, ranging from CAT1 to CAT7. UTP Category 3 or higher can be used for data communications, but Category 5 or higher is recommended. The other form of twisted-pair is STP, which has a shield that helps to prevent interference. Coaxial cable also comes in more than one form. RG-58 cabling or Thinnet is thin coaxial cable (about 1/4 inch thick) used on 10Base2 networks, while RG-59 cabling or Thicknet is thick coaxial cable (about 1/2 inch thick) used on 10Base5 networks. Fiber-optic cabling can be SMF, which is designed to transmit a single beam of light from a laser, while MMF is used to carry multiple beams of light at the same time. Such variations show a wide variety of media types to choose from when designing a network. Exam Objectives Fast Track 89 EXAM OBJECTIVES FAST TRACK Cabling and Connectors Overview Cabling is the wire or fiber medium that is used to connect computers and other network devices of your network together and used to carry the data that is transmitted between them. Coaxial cable, also referred to as coax, uses a single copper wire at the center of the cable to carry signals. The wire is surrounded by layers of insulation that protect the wire and its transmissions. Twisted-pair cables consist of pairs of wires that are twisted to reduce interference. This type of cabling may be unshielded or shielded. Fiber-optic cable carries digital data signals in the form of modu- lated pulses of light. Media Issues EMI is a low voltage, low current, high-frequency signal that can interfere with the electronic signals transmitted over cabling. EMI is also referred to as noise, as its signals come from outside sources and can corrupt data sent over cabling. RFI is caused by electromagnetic radiation in the radio frequency range. Crosstalk occurs when the signal of one wire bleeds onto another wire so that the electromagnetic field of one wire interferes with data transmission on another. Bandwidth is a measurement of the amount of data that can be passed over a cable in a given amount of time. Attenuation occurs when data transmitted over media weakens over distance. Cable Testers and Troubleshooting Tone generators are used to perform tests on phone and network lines by clipping to a wire, terminal panel, or standard modular jack and will aid in the identification of wires during the wire-tracing process. TDRs use signals that are sent down the cable to identify problems. An electronic pulse travels down the cable until it is reflected back, much like sonar. CHAPTER 2: Network Media 90 Wire map testers are often used on twisted-pair cabled networks to test for opens, shorts, or crossed pairs, and will provide information that may indicate improper wiring. Oscilloscopes can be used to determine when there are shorts, crimps, or attenuation in the cable. Simplex, Half-Duplex, Full-Duplex Simplex refers to data moving in a single direction. Half-duplex refers to data traveling both ways on the medium, but in only one direction at a time. Full-duplex refers to data traveling in both directions simultaneously. Cabling Ethernet is a standard for most networks used today, and includes specifications for 10Base2, 10Base5, and 10BaseT. CSMA/CD prevents devices from interfering with one another during transmission by detecting collisions of data. Fast Ethernet is a standard that provides speeds of 100 Mbps. Cabling Management Patch panels are primarily used for easy of use and flexibility, and gives the network administrator the ability to move connections quickly. There are multiple types of distribution facilities, the IDF (intermediate) and MDF (or main). Termination devices such as a 66 block or a 110 block are commonly used to provide termination point and are generally located in wiring closets in your facility. A patch and impact tool is used to terminate copper cabling to 66 and 110 blocks. For the Network exam you will need to know how to install commonly used wiring distribution systems. Distribution systems are nothing more than a term used to describe the hierarchical system of cross connections that lead to a local PBX, central con- centrator or the CO or elsewhere. Exam Objectives Fast Track 91 Media Standards 10Base2 uses coaxial cabling to transmit data at speeds of 10 Mbps across cable segments that are up to 185 m in length. 10Base5 uses coaxial cabling to transmit data at speeds of 10 Mbps across cable segments that are up to 500 meters in length. 10BaseT uses UTP cabling to transmit data at speeds of 10 Mbps across cable segments that are up to 100 m in length. The UTP cabling must be Category 3 or higher. 100BaseTX uses UTP cabling to transmit data at speeds of 100 Mbps across cable segments that are up to 100 m in length. The UTP must be Category 5 or higher. 10BaseFL uses fiber-optic cabling to transmit data at speeds of 10 Mbps across cable segments that are up to 2 km in length. 100BaseFX uses fiber-optic cabling to transmit data at speeds of 100 Mbps across cable segments that are up to 400 m in length with half-duplex communication or 2 km for full-duplex. 1000BaseT uses UTP cabling to transmit data at speeds of 1000 Mbps across cable segments that are up to 100 m in length. The UTP must be Category 5 or higher. 100BaseSX uses fiber-optic cabling to transmit data at speeds of 1000 Mbps across cable segments that are up to 550 m in length. 1000BaseLX uses fiber-optic cabling to transmit data at speeds of 1000 Mbps across cable segments that are up to 550 m (MMF) or up to 10 km (SMF) in length. 1000BaseCX uses fiber-optic cabling to transmit data at speeds of 1000 Mbps across cable segments that are up to 100 m in length. Connectors D connectors are shaped like the letter D and have pins that connect to a female D connector. RJ connectors are used to connect devices used for voice and data communications. CHAPTER 2: Network Media 92 DIX stands for Digital Intel Xerox, who developed the connector for use with an AUI that’s used with 10Base5 cable. BNC connectors are used to terminate coaxial cabling and provide connections to devices. There are a number of connectors available for fiber-optic cabling, including SC, ST, LC, and MTRJ. Media Types Twisted-pair cable comes in a variety of grades. UTP Category 3 or higher can be used for data communications, but Category 5 or higher is recommended. The difference between UTP and STP is that STP has a shield designed to keep interference out by protecting the wires inside from EMI caused by outside sources. RG-58 cabling or Thinnet is thin coaxial cable (about 1/4 inch thick) used on 10Base2 networks. RG-59 cabling or Thicknet is thick coaxial cable (about 1/2 inch thick) used on 10Base5 networks. SMF is optical fiber that’s designed to transmit a single beam of light from a laser. The beam of modulated light provides greater bandwidth and allows cable to be run over longer distances. MMF is used to carry multiple beams of light at the same time, using a light-emitting diode (LED) as a light source. Each of the beams is at a slightly different reflection angle within the core of the fiber. Other Media FireWire is a proprietary name for IEEE1394, which is an external bus that supports fast data transfer rates of 400 Mbps (in IEEE 1394a) and 800 Mbps (in IEEE 1394b). Wireless media is used to transmit data without cable. Transceivers are the portion of a network interface that transmits and receives electrical signals across the transmission media. Transceivers may be onboard (on a network card) or external. Self Test 93 EXAM OBJECTIVES FREQUENTLY ASKED QUESTIONS None of the workstations on the network are able to communicate Q: with each other. They use a thin wire coax Ethernet to connect to each other. What may be causing the issue? The backbone has been severed or improperly terminated. Find the A: point at which the bus became severed and reconnect it, make sure the backbone is properly terminated. You have a brand new UTP cable, but the workstation is still not Q: able to communicate on the network. The workstation worked with your test cable. What may be causing the issue? The brand new UTP cable may be a crossover cable. Obtain a regu-A: lar UTP cable. Is fiber the best networking media to implement in a standard of-Q: fice environment? Normally, due to cost limitations, offices are wired with UTP or STP A: and the data center is wired with fiber. Fiber is also often used as a backbone to connect one building to another. This is typically the most cost-efficient manner of providing high-speed networking for your servers and providing acceptable access speeds to your users. SELF TEST You are the network administrator of a 10BaseT network. On the 1. weekend, when few people are working, you run 110 m of cable to a new server that is being used as a file server. The cable is installed in a new section of the building, where no cabling currently exists. When you attempt to access files on the server, they are experienc- ing errors and corrupt data. Which of the following is most likely the cause of this problem? A. Bandwidth B. Attenuation C. Crosstalk from a neighboring cable D. CSMA/CD issues Your company uses UTP cable for all of its network connections 2. including workstations and servers. The users have reported CHAPTER 2: Network Media 94 problems connecting to one of the most important servers on the network and you have been called in to look at it, due to a possible physical security breach by a former employee. While examining the server, you find that a small battery-powered motor has been placed and is running next to the server’s network connection. What is causing the network problem? A. Electromagnetic interference B. Static electricity C. Transceivers D. Unknown, but the motor is probably unrelated You are designing a new network and are concerned about interfer-3. ence from other wires. Which of the following is most susceptible to transmission errors due to crosstalk? A. Coaxial B. UTP C. STP D. Fiber optic You are designing a new network for a grocery store. Cabling 4. will have to run along the ceiling, where there are a significant number of florescent lights. You are concerned about interference from these lights. Which of the following cable types could be used, which would not be susceptible to this type of interference? A. Coaxial B. UTP C. STP D. Fiber optic Your network uses vampire taps and AUI connectors to access data 5. from the network cable. Which of the following cabling types is being used? A. Thinnet B. Thicknet C. STP D. Fiber optic You are designing a 10Base2 network. In creating this network, what 6. distance limitation will you be facing when installing the cabling? Self Test 95 A. 100 m B. 185 m C. 500 m D. 2 km Examine the illustration shown in Figure 2.127. . Your network is a 10Base2 network, and it uses these connectors to attach to the network. Which of the following types of connectors is being used? A. RJ-11 B. DIX C. BNC Barrel Connector D. BNC T-Connector You have been hired by a small company to cable its network. 8. The company has offices in two buildings that are 300 m apart. Both of the offices have about 15 computers and the numbers are expected to grow in near future. All of the computers are within 90 m of one another. You need to decide on the cabling that will be used both in the individual buildings, and which will be used to connect the buildings LANs together. Which of the following will you do? A. Use UTP cabling in each of the buildings, and connect the two buildings together using 10BaseT cabling. B. Use fiber-optic cabling in each of the buildings, and connect the two buildings together using 10Base2 cabling. FIGURE 2.12 . used? A. RJ -11 B. DIX C. BNC Barrel Connector D. BNC T-Connector You have been hired by a small company to cable its network. 8. The company has offices in two buildings that are 300 m apart. Both. facilities, the IDF (intermediate) and MDF (or main). Termination devices such as a 66 block or a 110 block are commonly used to provide termination point and are generally located in wiring. closets in your facility. A patch and impact tool is used to terminate copper cabling to 66 and 110 blocks. For the Network exam you will need to know how to install commonly used wiring