Copyright Goodheart-Willcox Co., Inc. 72 Networking Fundamentals 2 1 3 1 2 Cable Pairs The difference between a 568A and 568B connection is the position of cable pairs 2 and 3. 10BaseT (802.3) specifies that cable pair 2 and 3 be used for communication. 568A or 568B may be used. A B 4 4 3 6 5 8 7 2 1 3 2 568A 3 6 2 1 2 3 568B 568A 568B 3 6 2 1 2 1 3 4 4 3 6 5 8 7 Figure 2-25 The 568A and 568B connection standards. A—The only difference between the two connection standards is the locations of pairs 2 and 3. B—The 10BaseT classification uses pairs 2 and 3. Either connection standard can be used. Goodheart-Willcox Publisher two pairs ( four individual conductors) that are cross-connected. Crossover cables are used to connect computers with other computers. Look at the wire map in Figure 2-26. Notice that pin 1 connects to pin 1, pin 2 connects to pin 2, and so on. When a two-workstation 10BaseT network is confi gured, a crossover cable must be used for the network cards to communicate. Cross-connecting the pairs allows a transmit signal from one computer to be sent to the receive pins of a network card on the other computer. Th is allows the computers to communicate without a hub. A crossover cable is not needed when a hub is used because the circuitry at each access port crosses the connection internally. Th ere- fore, a straight-through cable is used in this situation. Look at the hub in Figure 2-27. Notice that each access port number on the hub has an X beside it. Th is indicates the access port’s internal connection is crossed. Also, notice the uplink port. Th e uplink port serves a straight-through connection. It can be used to connect via a straight-through cable to an access port on another hub. Some network devices, like switches and network adapters, are Auto-MDIX compliant. Automatic medium-dependent interface crossover (Auto-MDIX) is an electronic chip technology incorporated into Gigabit Ethernet devices to auto- matically reassign pin functions and eliminate the need for a crossover cable. To veri- fy that the network device is Auto-MDIX compliant, look at the device specifi cations. Devices such as switches have a maximum transmission unit (MTU), which refers to the largest network-layer data unit that can be sent at one time, or the larg- est transmission unit. An MTU is adjustable, but it should only be adjusted by those with familiarity in doing so. Tech Tip A wire map is an illustration of the correct circuit path of conductors from one end of a cable run to the opposite end. Wire maps are used to illustrate proper cable connections for a technician who makes cable assemblies. 1.3 NET