 with this approach. It became more viable because the cost of active components was notably reduced. 11.6.2.1 CSMA/CD Description - Conventional Operation. Carrier sense multi- ple access with collision detection is defined by ISO/IEC 8802-3 and by ANSI/IEEE 802.3. This type of operation is often called Ethernet, which was initiated by the Xerox Corporation, Digital Equipment Corporation, and Intel. The version discussed in this paragraph is based on IEEE 802.3. Figure 11.7 relates CSMA/CD protocol layers to the conventional OSI reference model described in the previous chapter. The figure also iden- tifies acronyms that we use in this description. The bit rates generally encompassed are 10 Mbps and 20 Mbps. We will also briefly cover an IEEE 802.3 subset standard for 100-Mbps operation. The model used in this present discussion covers the 10-Mbps data rate. There is also a 100-Mbps CSMA/CD option, which is described in Section 11.6.2.2. There will also be a 1000-Mbps variance of this popular MAC protocol. The medium described here is coaxial cable. However, there is a trend to use twisted wire pair. The LAN station connects to the cable by means of a medium access unit (MAU). This connects through an attachment unit interface (AUI) to the data termi- nal equipment (DTE). As illustrated in Figure 11.7, the DTE consists of the physical signaling sublayer (PLS), the medium access control (MAC), and the logical link con- trol (LLC). The PLS is responsible for transferring bits between the MAC and the cable. It uses differential Manchester coding for the data transfer. With such coding the binary 0 has a transition from high to low at midcell, while the binary 1 has the opposite transition. CSMA/CD LAN systems (or Ethernet) are probably the most widely used type of LANs worldwide. We would say that this is due to their relatively low cost to implement and maintain and to their simplicity. The down side is that their efficiency starts to drop off radically as the number of users increases, as well as increased user a