ther, the Intelligent Network was a telephone Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Transport Technologies Chapter 7 company attempt to engineer vendor independence, more automatic operation, and some "intelligent" new services into existing network architecture. However, even as it rolls out and matures, the Intelligent Network is being superseded by a Stupid Network, with nothing but dumb transport in the middle and intelligent user-controlled endpoints, whose design is guided by plenty, not scarcity, where transport is guided by the needs of the data, not the design assumptions of the network. Isenberg continues: A new network "philosophy and architecture," is replacing the vision of an Intelligent Network. The vision is one in which the public communications network would be engineered for "always-on" use, not intermittence and scarcity. It would be engineered for intelligence at the end-user's device, not in the network. And the network would be engineered simply to "Deliver the Bits, Stupid," not for fancy network routing or "smart" number translation. ATM Technology Overview Because ATM plays such a major role in networks today, it is important to develop at least a rudimentary understanding of its functions, archi- tectures, and offered services. ATM Protocols Like all modern technologies, ATM has a well-developed protocol stack (see Figure 7-7) that clearly delineates the functional breakdown of the service. The stack consists of four layers: the upper services layer, the ATM adaptation layer, the ATM layer, and the physical layer. The upper services layer defines the nature of the actual services that ATM can provide. It identifies both constant and variable bit rate ser- vices. Voice is an example of a constant bit rate service, while signaling, IP, and frame relay are examples of both connectionless and connection- orie