l components must be fault tolerant (or even redundant in some cases) and line cards must be hot pluggable, meaning that they can be replaced without bringing down all of the network equipment. These are very different requirements from a customer premise router. Another type of WAN edge router is the MSR out of which the Multiservice Providing Platform (MSPP) has evolved. MSPPs are essentially SONET add/drop multiplexer (ADM) equipment that combines IP routing and ATM switching. Due to their versatility and performance, network proces- sors are expected to be especially useful in the implementation and delivery of MSPP products. Some companies use the term metropolitan area network (MAN) as another context. Although the technical environment of the MAN is essentially similar to the one encountered in the WAN, the cost of deployment and the economics of justifying product investment are different. This enables less expensive technologies to be adopted for the implementation of similar solutions. MAN equipment is an interesting business context, but for our technical purposes, we will consider it just as another example of a WAN technology that consists of the traditional access and edge networks, as shown in Figure 3.2. We will no longer single it out specifically. This is because the design requirements of net- work equipment for MAN applicability (especially pertaining to network processors, switch fabrics, and traffic managers) are easily deduced by the edge and access network equipment requirements. In the midst of all these combinations of functionality, protocols, line interfaces, and wire speeds, one should not forget the ever-present need to consolidate along all the more recent techniques legacy voice traffic, although at some point this need is bound to become more or less obsolete. traffic is the most lucrative service a carrier could offer at this point. It is usually delivered on Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-