Copyright Goodheart-Willcox Co., Inc. 75 Chapter 2 Network Media—Copper-Core Cable Power over Ethernet (PoE) Th e Power over Ethernet (PoE) IEEE standard 802.3af specifi es the supply of small amounts of electrical power to network devices, such as cameras, IP phones, wireless access points, speakers, and phone or PDA chargers. Th e amount of power delivered is approximately 13 watts at 48 volts. Th e cable used for PoE must be rated as Catego- ry 5 or better. Two pairs of cables are used for network communication and one pair is used to supply the electrical power. A more electronically sophisticated method of PoE is used for Gigabit networks in which all cable pairs are used to carry network communication. Electrical power is supplied via two of the existing cable pairs that provide communication. A more technical explanation of how power is provided over a communication cable is beyond the purpose of this textbook. To learn more about the electronic aspect of PoE, visit www.poweroverethernet.com. For detailed electronic specifi ca- tions, check the Texas Instruments web page focus.ti.com/docs/prod/folders/print/ tps2370.html. A common PoE application is building and area security when electrical power is not readily available. Using PoE is very cost-eff ective when compared to installing new electrical circuits to power devices such as cameras. IEEE 802.5 Standard Th e IEEE 802.5 standard describes the token ring network. Th e token ring network uses the token passing access method and is confi gured in a ring topology. Token ring networks operate at 4 Mbps, 16 Mbps, and 100 Mbps. Token ring can be used with proprietary cable, such as IBM design or UTP and STP. Th e maximum num- ber of nodes allowed for a token ring network varies according to the network dis- tance, speed, cable media, and equipment used. Always check with the manufactur- er for the latest specifi cations. Th is is a very old technology and you are unlikely to discover it today. However, it was pivotal in the history of networking, so it still ap- pears in many networking textbooks and certifi cation tests, like the CompTIA Net- work+. While a token ring network can be wired as a physical ring, as shown in Figure 2-31, most token ring networks use a multiple access unit (MAU) for a center 1.3 NET Tech Tip Some token ring networks do not use UTP as the network media. They use proprietary cable, but the electrical charac- teristics are similar. BNC connector Network interface card Coaxial cable Figure 2-31 Token ring network using coaxial cable. When a token ring network uses coaxial cable, it resembles a physical ring. Goodheart-Willcox Publisher