opic we are covering here, but it is important one for the overall architecture of a switching system. The intention is to highlight overall systems-related issues. In some designs, the scheduler will not allow packets to enter the switch fabric core at all before it ensures that a link to the desired output is actually available. This is not a magic solution, however, as planning more internal activity than there is switching bandwidth (a sad situation known as over- commitment of the switch fabric) will inevitably lead to packet loss. Therefore, the burden rests squarely on the shoulders of the scheduler to ensure that incoming packets can be admitted. Some systems use in-band or out-of-band backpressure (see for example [a] Katevenis, M., D. Serpanos, and E. Spyridakis. "Switching Fabrics with Internal Backpressure Using the ATLAS I Single-Chip ATM Switch." Proceedings of the IEEE GLOBECOM'97 Conference Phoenix, AZ [November 1997]: 242-246. It is available online at http://archvlsi.ics.forth.gr/atlasI/, in Postscript [230 KB], or gzip'ed Postscript [53KB] and [b] Motorola text at http://e-www.motorola.com/ collatoral/SNDF2002_N302.pdf). This technique minimizes the amount of necessary buffers espe- cially in multistage switches. This is because whenever an output is blocked, special in-band or out- of-band backpressure signals communicate this condition to previous upstream stages and prohibit them from forwarding more packets downstream. In-band backpressure removes useful bandwidth, but it simplifies the silicon design. Out-of-band backpressure mechanisms make the design more com- plex, but do not waste switching bandwidth when applied. Once it is activated, backpressure is not a remedy against the abundance of incoming traffic. As a result, it will simply cause input buffers to be filled up instead, which sometimes may lead to packet loss at the inputs. In order to put things into perspective, notice that when transient congestion occurs and as a result transient backpressure is being experienced, the conce