 is responsible for the traffic origination must assume that flows will run on the best-effort route that is assigned in the router regardless of priority. Although the case of MPLS is a slight deviation from our subject, it is inside the same QoS realm. We will obviously not discuss MPLS in detail here. For more information, refer to the respective lit- erature at the end of the chapter. However, it is interesting that in MPLS, specific bits are marked onto packets (or labeled), and explicit paths, which are called label-switched paths (LSPs), are assigned to packet flows by the network routing or switching equipment. This assignment is accomplished by the generation of corresponding packet labels. The appropriate label is contained in an MPLS header that now becomes a prefix to each IP packet. Policies that span the range of possible network applications must be established and then, based on these policies, labels are mapped/assigned to individual applications. We cannot help but notice the striking similarity with the process of assigning applications to classes of traffic in a QoS realm as previously discussed. These labels will then be used by the label- switched routers (LSRs) in the MPLS network. More specifically, it is based on the content of the labels that the routers make on-the-fly and per-hop decisions as to how to appropriately forward each packet to the next downstream router along the stipulated path that is associated with the specific label. 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. TRAFFIC MANAGERS 320 NETWORK PROCESSORS Interestingly, MPLS can also work across network boundaries as long as network operators use the same version of MPLS on their routers. From a QoS standpoint, MPLS has the important advantage of directing packet flows along spe- cific paths. It therefore allows the implementation of sophisticated tra