 on the PI40 fabric. It uses eight PI40X and two PI40C chips. (Source: Agere) 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. SWITCH FABRICS SWITCH FABRICS PI-40SAX Fabric cards FIGURE 14.19 A standalone switching system using the PI-40SAX fabric chip. (Source: Agere) The PI40 switch fabric offers a flexible and programmable queuing structure based on multiple routing queues that can be associated with a single fabric port in order to ensure significantly improved QoS capabilities at that specific fabric port. Each routing queue has two scheduling subqueues-one for the real-time traffic (such as voice over TDM traffic or streaming video) and one for the non-real- time traffic. QoS scheduling is handled on an SP basis for delay-sensitive traffic with a bandwidth/ delay guarantee for real-time traffic that may not be as sensitive to delay, on a granularity basis of 478 cells per second, or even on the basis of scheduling any excess bandwidth for so-called best-efforts traffic. Fairness is provided by selective backpressure and the entire system can be configured as a cen- tralized, distributed, stackable, or single-chip fabric. The distributed fabric configuration is done with each PI40C crosspoint operating independently from each other. If one fails or is removed, the oper- ations of any other PI40C in the system are not affected. In its maximum configuration, up to 64 first- stage and 64 third-stage PI40X devices can be connected to 40 PI40C devices to create a 2.56 Tbps switch fabric capacity. By replacing the PI40C devices with a higher-capacity crosspoint element, this configuration can achieve a total throughput of 10 Tbps. As part of the company's Integrated Development Environment (IDE), a performance simulator is available for the PI40 switch fabric. It is fully integrated with a powerful traffic generator (that can be made to genera