sample of the effort and diligence needed to come up with a system solution. 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. SYSTEMS ENGINEERING ISSUES NETWORK PROCESSORS Switch Fabric The system designer next starts conceptualizing some deeper insights about how the project will evolve. The vendor proposes the switch fabric PI-40SAX card that can be used in the lower configu- ration of the MSR, but as the designer also has in his or her mind the follow-on generation of the prod- uct, Agere's PI40C and PI40X cards sound like the desired solution in an upgraded system. As shown in the Agere technology chapters, the PI40X is the crossbar and PI40C is the scheduler and queues. Agere has them as full-size cards in their Festino development environment, but our designer is preoccupied with the optimization of the overall MSR design. Hence, a design decision is tacitly made that the PI40X and PI40C cards will have to be redesigned to become half-size cards. Agere offers the design guidelines, but the designer's organization is responsible for producing its own (half-size now) PI40X and PI40C cards. (We are using the same names here but we will not repeat them from now on in this discussion; these names correspond to the in-house designed half-size switch fabric cards.) These must be combined as two of each (for redundancy) in our chassis. The designer must also keep in mind that the PI40X chips are unidirectional; hence, they must be doubled for duplex solution. Also, one PI40C can be combined with up to four PI40X fabric chips. Assuming that the redesigned PI40X cards are half-size and that two of them can occupy one slot, then in a combination of 1+5 (meaning one scheduler PI40C and four crossbars PI40X), three slots must be filled-two that will individually contain two of the new half-size PI40X cards (for a total of four PI40X) and one that con