SYSTEM ADMINISTRATION Chapter 4 Network Media, Connectors, and Their Characteristics

Understanding Ethernet Standards The IEEE 802 standard addresses hardware that interacts with the Physical and Data Link layers of the OSI Model. The two most common media are twisted pair wire and coaxial cable.

Twisted Pair Cable Twisted pair wire, the same type used to connect telephones, is used to connect network devices together. UTP contains four wire pairs (eight wires total). Each type includes at least two pairs of insulated copper wires that are twisted together and housed in a plastic sheath. Higher categories have more twists per foot, which provides for better throughput and less chance of crosstalk or outside electromagnetic interference (EMI). (continued)

Twisted Pair Cable (continued) For 10Base-T networks, the twisted pair cabling must be rated at a minimum of Category 3, although Categories 4 and 5 may also be used. Twisted pair wire used in data networks can be either unshielded (UTP) or shielded (STP). The sheath or exterior covering of the cable pairs can be either plenum grade or non-plenum grade. Twisted pair cabling uses RJ-45 connectors.

10Base-T Shielded or unshielded twisted pair cable is used. RJ-45 connectors are used to terminate one or more ends of the cable. The cable may also be terminated at a punch-down block or in the back of a patch panel. Each station has its own network cable and it is not shared with any other stations. Network speeds are 10 Mbps. A maximum of 1024 stations are allowed per network. The maximum distance of a cable run is 100 meters (328 feet).

100Base-T 100Base-T Ethernet works just like regular Ethernet except that it can obtain data transfer speeds up to 100 Mbps. Fast Ethernet can be divided into two categories: –100Base-TX –100Base-T4 Both 100Base-TX and 100Base-T4 work with twisted pair cable.

100Base-T4 100Base-T4 can attain data transfer speeds up to 100 Mbps over Category 3 cable. 100Base-T4 uses four pairs of wiring (all eight wires).

100Base-TX 100BaseTX requires Category 5, unshielded twisted pair cable. All associated networking hardware, such as patch panels and connectors, must comply with Category 5 standards.

10Base-2 - Thin Coaxial Cable Coaxial cable has two conductors, a center copper core that is shrouded by insulating Teflon or plastic foam, and a foil wrap or a braided metal shield that covers the insulating plastic foam. The inner core carries the electrical signals while the outer foil wrap shields against noise. Coaxial cable is commonly used in a bus configuration. 10Base-2 networks use RG-58 cable (Thinnet). Cable types RG 58 A/U or RG 58 C/U are commonly used. (continued)

10Base-2 - Thin Coaxial Cable (continued) Each end of the segment must be equipped with a 50-ohm terminating resistor. Pieces of coaxial cable may be no shorter than 0.5 meter (1.64 feet) in length. This means that the minimum spacing between network connections must be at least 0.5 meter. Thinnet segments may be a maximum of 185 meters (607 feet) long.

10Base-5 - Thick Coaxial Cable Thick coaxial cable, also known as Thicknet (RG-8/RG- 11), is commonly used in 10Base-5 networks. Thicknet is well suited for network backbones or for connecting hubs. Uses RG-8 or RG-11 cable, which has a solid center conductor. Uses a thick (0.4-inch diameter) and inflexible coaxial cable. The outer casing of the cable may be polyvinyl chloride (PVC), which will be yellow in color, or Teflon, which will be an orange or brown color. Plenum cable may be required to meet fire regulations. (continued)

10Base-5 - Thick Coaxial Cable (continued) Must be terminated at each end with 50-ohm terminators and should be grounded at one end for electrical safety reasons. A maximum of 100 devices may be attached to a segment. Pieces of Thicknet may be no shorter 2.5 meters. This means that the minimum spacing between network connections must be at least 2.5 meters. Each segment has a maximum length of 500 meters, which may be extended with repeaters. A maximum of five segments may be used. Transceivers are used to attach nodes to the cable.

Fiber-Optic Cabling Instead of using copper wire to transmit electrical signals, fiber-optic cabling uses light-conducting glass fibers as its core. Data is then transmitted either through pulses of light that are sent by a laser or light-emitting diodes (LED). (continued)

Fiber-Optic Cabling (continued) There are several different types of fiber-optic cabling: –Single-mode: Contains a single, tiny strand of fiber-optic glass, usually 7.1 or 8.5mm in diameter. Single-mode fiber is typically used in telephone applications, cable television, or as a backbone. –Multimode: In multimode fiber, the core is usually 62.5 mm in diameter, much larger than that used by single- mode. Multimode can handle many rays at once, making it ideal for voice and data applications. Multimode cable is the most commonly used in computer networks. –Simplex fiber: Simplex is a cable containing a single strand of fiber. –Duplex fiber: Duplex is a cable with two strands of fiber bound together in separate jackets. (continued)

Fiber-Optic Cabling (continued) Must follow the prescribed bend radius when installing (i.e., if the cable is bent too sharply, it will break). Difficult to terminate and there are several types of connectors in use. Must ensure you purchase the correct connectors, especially when working in an area where fiber has already been installed. Fiber-optic cable is expensive. When buying in bulk, expect to pay about $1.00 per foot. Fiber-optic devices, such as network cards and media converters, must also be used. (continued)

Fiber-Optic Cabling (continued) Very secure since data is transmitted using pulses of light rather than electrical signals. Resistant to EMI since it does not transmit electrical signals. Maximum length is measured in miles, approximately 2.4 (or 4 kilometers). Does not attenuate very quickly. The most common connectors used for fiber-optic cabling are either ST or SC connectors.

100Base-FX 100Base-FX uses fiber-optic cabling to transfer data at 100 Mbps, while maintaining Ethernet standards. Advantages: –It provides a fast, reliable, and secure connection. –It is highly resistant to EMI. –Can transmit up to approximately 4 kilometers (approximately 2.4 miles). Disadvantages –Very expensive, especially when compared to 100Base-T using copper wiring. –It is more difficult than copper to install and terminate. –Must also purchase networking hardware with fiber connections or purchase media converters.

Gigabit Ethernet Gigabit Ethernet is a transmission technology that is based on Ethernet standards. Provides a data transfer rate of 1 billion bits per second (one gigabit). Frequently used as the backbone in large-enterprise networks. Fiber-optic cable is the primary medium used on Gigabit Ethernet networks, although copper cable may be used for very short distances.

Troubleshooting Network Cabling Problems Although each cable type has some unique features, there are some features that they all have in common. The steps listed below can be used with all cable types: –Ensure the connectors are secure. Pull lightly on each connector to ensure it is firmly attached. –Check to make sure the connector is installed correctly. –Check the cable for severe kinks or damage. Replace damaged cables. –Measure the cable to ensure it does not exceed maximum distance limitations. –Make use of cable testers if the wire is suspect. –When using copper cable, ensure they do not cross fluorescent lights or other sources of electromagnetic interference.

Twisted Pair Cable Look at the wire colors in the connector. Are the wire pairs inserted correctly? Check both ends. Ensure you are not using a crossover cable instead of a straight-through cable, and vice versa, depending on the intended purpose of that wire. Check the length of all cables involved in the run. For example, the maximum length of twisted pair cable is 100 meters. This means that if the patch cable (running from the computer to the wall jack) is 10 meters long, the cable run (from the back of the wall jack to the hub or switch) cannot exceed 90 meters.

Coaxial Cable Termination is one of the most common problems in a network using coaxial cable. When more than one computer has trouble communicating, always check that the connector is attached. If you suspect a bad connector, try another one. Ensure you are using the right type of wire. Do not use cable intended for television installations on a computer network. When working with Thicknet, ensure the vampire taps are secure. Remember the rule: –5 total segments –4 repeaters –3 segments with devices

Fiber-Optic Cable Observe the bend radius. The glass fibers may break when bent too severely. Fiber-optic cable should be laid in a metal raceway or conduit for protection. Check the connectors. Adding connectors to fiber- optic cable is tedious, exacting work and requires practice.