itch takes note of the FECN bit, which tells it the following: "I just came from that switch back there, and it's extremely congested. You can transmit stuff back there if you want to, but there's a good chance that anything you send will be discarded, so you might want Figure 7-4 A frame encounters congestion in transit. Frame with FECN bit set 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. Transport Technologies Chapter 7 Figure 7-5 BECN bit used to warn a station that is transmitting too much data (in violation of its agreement with the Frame with BECN bit set switch) to wait awhile before transmitting." In other words, the switch has been notified of a congestion condition, to which it may respond by throttling back its output to allow the affected switch time to recover. On the other hand, the BECN bit is used to flow-control a device that is sending too much information into the network. Consider the situation shown in Figure 7-5, in which a particular device on the network is transmitting at a high volume, routinely violating the CIR and perhaps the EIR level established by mutual consent. The ingress switch-that is, the first switch the traffic touches-has the ability to set the BECN bit on frames going toward the offending device, which carries the implicit message, "Cut it out or I'm going to hurt you." In effect, the BECN bit notifies the offending device that it is violating protocol, and continuing to do so will result in every frame from that device being discarded- without warning or notification. If this happens, it gives the ingress switch the opportunity to recover. However, it doesn't fix the problem- it merely forestalls the inevitable, because sooner or later the intended recipient will realize that frames are missing and will initiate recovery procedures, which will cause resends to occur. However, it may give the affe