Copyright Goodheart-Willcox Co., Inc. 71 Chapter 2 Network Media—Copper-Core Cable IEEE 802.3 Media Access Ethernet networks use a media access method called carrier-sense multiple ac- cess with collision detection (CSMA/CD) to control and ensure data delivery. CSMA/CD works by allowing a workstation to listen for data traffi c on the network before transmitting data. When the network is silent, the workstation transmits data. However, if another workstation submits data at the same time, the data collides on the network. When this happens, the two workstations wait a random period before retransmitting the data. Th e random period is less than a fraction of a second. A typi- cal network can transmit thousands of data packets in one second. Collisions usually remain unnoticed on a properly installed network. A poorly designed network may operate slowly as a result of too many collisions. Data collision is an inherent prob- lem with Ethernet communication. When two data packets collide, they become cor- rupted and cannot be delivered. Breaking down the acronym will help you better understand CSMA/CD as a standard for network communication. CSMA/CD can be separated into three dis- tinct pairs of letters that correspond to words that explain the operation require- ments that must be met to match the CSMA/CD standard. Carrier sense (CS) means that a network interface card can sense when data is transmitted on a network cable. Multiple access (MA) means that the network cable provides simultaneous access to all network interface cards connected to the cable. Collision detection (CD) means that the network interface card can detect when a collision has occurred and will automatically resend the damaged packet. Today, however, what is most often used is carrier-sense multiple access with collision avoidance (CSMA/CA), works much like CSMA/CD but tries to avoid col- lisions by waiting until there is a brief lull in network traffi c before sending out a packet. IEEE 802.3 Wiring and Connections Wiring and connectors used for networking were fi rst derived from the existing tele- phone communication industry. Even today, many of the cable standards apply not only to networking but also to other communication systems. Th is section introduces the basics of twisted-pair network cable, connectors, and standards. Th e two main cable termination standards in use for twisted-pair ca- ble are 568A and 568B as described by the TIA/EIA organization. 568A and 568B When installing an RJ-45 connector, it is important that the conductors, which are color-coded, be inserted into the appropriate pin area. Two standard connections are recognized by industry: 568A and 568B. Long before standards existed, there were two common ways to make an RJ-45 connection. Since the industry was divid- ed, both became standards but are denoted by the letters A and B. Th e only real dif- ference in the connections is the color of the conductors inserted into the pin areas. Other than the color of the conductors, the electrical qualities are the same. Look at Figure 2-25. Compare the two standard connections, 568A and 568B, in Figure 2-25A. Notice that for the 10BaseT classifi cation, Figure 2-25B, each connector uses only two pairs of conductors from the cable: the orange pair and the green pair. Th e other two pairs are not used for communication in a 10BaseT network. UTP cables have two common classifi cations of assembly: straight-through and crossover. A straight-through cable is constructed with each numbered pin con- necting to the matching numbered pin on the opposite end of the cable. Straight- through cables are used to connect computers with hubs. A crossover cable has 1.3 NET 2.1 NET