cGraw-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 More importantly, however, Agere has recently introduced a protocol-independent switching fabric-the PI40 family of chips, which can scale from a single-chip 40 Gbps fabric to a multichip 2.5 terabits per second (Tbps) system, as shown in Table 14.1. The PI40 supports fabric port rates from OC-12c to OC-768c and connects without any glue logic to the company's 10 Gbps network processors. It consists of three types of devices: The PI40X, a full-duplex switch fabric that has up to 40 Gbps throughput and can handle issues such as aggregation and concentration as well as queuing and scheduling The PI40C, a full-duplex 160 Gbps crossconnect device for crossbar arbitration and switching The PI40SAX series of 20/40 Gbps protocol independent stand-alone switching fabrics The PI40X works in two modes: ingress and egress. In the ingress mode, the PI40X multiplexes incoming traffic to the crossbar switching stage. Traffic is buffered and queued separately per egress port taking a worst-case approach. The queuing structure is a good way to provide a sense of traffic isolation and fairness. A QoS-capable schedule handles all the queues, and traffic cells are forwarded to the crossbar planes over multiple 2.5 Gbps serdes links. For large systems, bandwidth can be dynamically allocated by the formation of link groups. Embedded memory is also present and, more specifically, 8K cells handle unicast traffic and 1K cells handle multicast traffic. The crossbar itself is a 64X64 switching matrix with each link being 2.5 Gbps. Lossless self- routing functionality is provided by the internal QoS-aware arbitration logic. The crossbar can be con- figured as 1 off 64X64 matrix, 2 off 32X32 matrices, 4 off 16X16 matrices, 8 off 8X8 matrices, 16 off 4X4 matrices, or even 32 off 2X2 matrices. In the egress mode, the PI40X demultiplexes the