ve systems designer a wider dimension. From a performance standpoint, the configuration can offer low latency (because no queuing occurs in the data path crossing the fabric core). However, may suffer from the need to reorder traffic because the presence of a shared medium (the fabric core) necessitates a contention resolution that may affect the sequential ordering of internal transfers. Multicast traffic is not natural for this approach SO extra design creativity is required to adequately handle this type of data with the arbitrated crossbar when it is implemented using the distributed switching. 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 An arbitrated crossbar can be combined with traffic management and packet buffering also at the ingress ports, whereas the egress ports may or may not be equipped with queuing capabilities. This configuration allows better systems design and performance fine-tuning by enabling a close relation- ship between the switch fabric and traffic management, which enables the QoS to be scaled in a very fine granular and sophisticated way. This is also discussed in Chapter 15, "Traffic Managers." Shared Memory Switches In a shared memory switch, as shown in Figure 14.10, the inputs feed a multiplexer, which sequen- tially stores the (now serialized) incoming packets in a common memory bank that lies in the heart of the switch fabric. This embedded memory is shared by both inputs and outputs for the storage of frames/packets and for the management of queues. A control module is responsible for the extraction of stored cells/frames from the shared memory. By their recombination, it reassembles the original packets into an output stream, which is then subjected to the opposite operation from the one that occurred at the input. In other words, it is demultiplexed and its parts are rout