y decided that Sutton did not have to serve his entire sen- tence of two life sentences plus 105 years because of failing health. So, on Christmas Eve, 1969, Sutton, now 68, was released from Attica State Prison. And in 1970, Sutton did a television commercial to promote the New Britain, Connecticut, Bank and Trust Company's new photo credit card program. You have to love the little ironies in life. Sutton died in 1980 in Spring Hill, Florida, at the age of 79. So what does Willie Sutton have to do with the OSI Model and ser- vice providers? Not much-but his career does. Today's service providers are climbing the food chain because the money is up there with the customers. Yes, of course there is money to be made at the Physical Layer end of the model, but the sustainable, growable rev- enues are up where services can be customized endlessly to meet the changing needs of customers. More Now About the Inner Workings of the OSI Model The func- tions of the model can be broken into two pieces, as illustrated by the dashed line in Figure 2-12 between layers three and four that divides the model into the chained layers and the end-to-end layers. 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. Protocols Chapter 2 The chained layers are made up of layers one through three: the Phys- ical Layer, the Data Link Layer, and the Network Layer. They are respon- sible for providing a service called connectivity. The end-to-end layers on the other hand comprise the Transport Layer, the Session Layer, the Pre- sentation Layer, and the Application Layer. They provide a service called interoperability. The difference between the two services is important. Connectivity is the process of establishing a physical connection SO that electrons can flow correctly from one end of a circuit to the other. There is little intelligence involved in the process; it occurs, 