e projections. This has proven to be the case when carriers in developed countries promote attractive smartphones which add unexpected amounts of Internet and e-mail traffic that networks are not prepared to handle. It takes enormous investments and long lead times to add capacity to complex, modern networks. THE STRUCTURE OF THE INTERNET The Internet is made up of routers that direct traffic based on addresses contained within the headers of data packets. In an effort to reduce delays, Content Delivery Net- works (CDNs) install servers at their own locations and that of the carrier's site at Internet's edges, thus placing content closer to the end users that request it. Edge Routers Edge routers are located at the edge of a carrier's network where they connect to cus- tomers and to other routers. They are often located at Points of Presence (POPs) where multiple providers connect to the Internet. The edge of a network needs to support complex applications, protocols, and video. Edge routers must support multiple protocols, including Internet Protocol ver- sion 6 and version 4 (IPv6 and IPv4), Multi-Protocol Label Switching (MPLS), and complex accounting software to track packet usage per customer. On MPLS networks, edge routers attach labels as described in Chapter 5, "Broadband and Wide Area Net- work Services," that include information regarding addresses, protocol, and Quality of Service (QoS). For more information about IPv4 and IPv6 addressing protocols, see the section "Address Structures," later in this chapter. The Internet In addition, edge routers commonly handle aggregated Digital Subscriber Line Access Multiplexer (DSLAM) traffic in various formats such as older Asynchronous Transfer Mode (ATM) and Time-Division Multiplexing (TDM); therefore, routers need to support both newer and older variations of IP. ATM protocols use complex asynchronous multiplexing technologies to transmit voice, data, and video. They are more costly and complex to operate and less flexible than networks based on IP; they are 