in a single access channel (see Figure 7.17). ATM Applications There are many key applications for ATM. The ATM standard began in the carrier community as a means of reengineering the PSTN to meet the demands of future applications. As Frame Relay networks began to see the demand to accommodate voice and video, they also began to institute ATM in their core in order to adminis- trate service guarantees. The same goes for the Internet backbone, especially where Packet-Switched Networks Voice ATM Multiplex Multiplexed Cell Stream Video Figure 7.17 Mapping services into ATM there's an interest in providing more than just consumer Internet access but also business-class services, where the customer wants some SLAs tied to QoS and net- work performance. There's also a need for ATM in VPNs that carry multimedia traffic, and you can also use it when you want to reengineer the network environment to be inte- grated-for example, replacing individual PBXs for voice and LAN switches for data with an enterprise network switch that can integrate all your traffic into one point at the customer edge. Finally, ATM can be used to enhance or expand campus and workgroup net- works; that is, it can be used to upgrade LANs. In the early days of ATM, one of the first marketplaces where it saw adoption was in the LAN community. If you wanted to make a move to a campus network that could support 155Mbps or 622Mbps, the only solution was to go to an ATM environment. However, Gigabit Ethernet is much less expensive technology and transition path than ATM. To go from 100Mbps Ethernet to ATM means going to an entirely new technology. It's an investment in an entirely new generation of equipment, with a requirement for an entirely new set of technical skills. Many more applications developers are knowl- edgeable in other techniques, such as IP, than in ATM. However, Gigabit Ethernet doesn't require learning a new protocol, which is a benefit for network engineers. Gigabit Ethernet also has a much lower cost in terms of the actual components 