d as a backbone network to interconnect Ethernet or token ring LANs. Now that simpler high-speed technologies have become available the importance of FDDI has decreased. There are many other standards for LANs but the vast majority of LANs in use utilize Ethernet technology because it is simple and inexpensive. In the following sections we concentrate on Ethernet networks. Introduction to Telecommunications Network Engineering 6.5.2 Multiple-Access Scheme of the Ethernet The MAC layer in the Ethernet is defined in ISO 8802-3/IEEE 802.3 and this access method is called CSMA/CD. This abbreviation stands for the following: Carrier sense (CD) means that a workstation senses the channel and does not transmit if it is not free. Multiple access (MA) means that many workstations share the same channel. Collision detection (CD) means that each station is capable of detect- ing a collision that occurs if more than one station transmits at the same time. In the case of a collision, the workstation that detects it immediately stops transmitting and transmits a burst of random data to ensure that all other stations detect the collision as well. The original standard defined thick and thin coaxial cable networks operating at 10 Mbps. Many physical cabling alternatives have been added to the standard and the twisted-pair network 10BaseT has replaced most coaxial networks. In response to the increasing need for higher data rates in today's LANs, 100/1,000-Mbps Ethernet networks are released. The Ethernet offers a seamless path for the development of LANs into higher speeds while the present infrastructure of the network remains unchanged. To support this smooth development of LANs, the latest high-rate networks still use the same frame structure and the same managed object specifications for net- work management. We now explain the operation of the CSMA/CD multiple-access scheme and the network structure of the original IEEE 802.3. The multiple- access method is most easy to understand with the help of bus-type coaxial cable net