ttrition, consoli- dation, and inevitable evolution in this rapid market. THE OVERRIDING REQUIREMENTS FOR NETWORK EQUIPMENT The four different network realms illustrated in Figure 3.2 are characterized by various requirements, which are summarized in this section. We intend to highlight the following two points: How the systems designer has to cope with some very specific constraints imposed on him or her by the context within which the equipment will be called to operate. How to trigger the imagination of the reader as to how the network-processing platforms are called to deliver solutions for the different problems that are encountered at each level in this conceptual hierarchy. For CPE equipment, which will require more packet-based services in the future as new services are introduced into this market space, the systems designer wants to ensure that the equipment has the following characteristics: Is interoperable with the access network's behavior at layers 1 and 2 and potentially with the edge equipment's expectations at layer 3 and above in the service provider's network (for example, appli- cations like e-mail protocols such as Simple Mail Transfer Protocol [SMTP] and Post Office Protocol [POP] or widely used layer 4 protocols such as TCP). Can handle the WAN wire speed. Is designed and proposed economically. Does not require large physical space for its deployment SO that it can be offered to multiple envi- ronments without undue customer resistance. Is easy to manage and configure remotely. Is highly integrated SO multiple services can be offered through it. Allows room for modular future expansion. Access network equipment, which is the first layer of consolidation and the last layer of distribu- tion by the service provider of traffic to and from multiple users, has a different set of essential require- ments. The systems designer focuses primarily on the following: A large-scale and (as much as possible) low-cost aggregation of multiple physical connections to subscribers. This is usually accomplishe