4 NETWORK PROCESSORS We discussed earlier in Chapter 1 how the original switch and router concepts have slowly merged with each other to form a functionality that spans the multiple layers of protocol stacks. This is the main reason why we usually use these terms interchangeably throughout this book. In the specific cases where the two concepts must be distinguished from one another, however, we clarify which term will be used. In the industry, the switching/routing equipment is usually referred to by the physical place where it is installed, not by the corresponding stack layer at which it operates. Figure 3.1 shows the conceptual layering of multiple interconnected networks in the converged network that we are discussing. The bottom of the hierarchy contains the enterprise network, which is also known as the customer network or customer premises. The term customer premises equipment (CPE) was created from this concept, although it was not originally coined in a packetized-data network concept. The enterprise network corresponds to the typical day-to-day user's Ethernet and Fast Ethernet networks that are located in companies, universities, and SO on. The enterprise network contains one or more local area networks (LANs) on one side connecting ordinary user stations, such as PCs, with shared access to common resources, such as printers, faxes, and SO on. In addition, this network contains faster local networks that enable an organization to connect its servers, its storage subsystems, and SO on. Some of these faster enterprise LANs are Gigabit Ethernet networks. A new type of switch has recently evolved that serves the latter community of servers. This switch may handle intelligent load balancing by switching traffic to and from specific servers, or it may merely manage a storage server farm or arrays of disk storage racks connected through a dedicated storage area network (SAN). The latter context shows the advantages associated with offloading the traditional LAN. A trend is formed toward creating newer IP-bas