te subscriber. Authenticating a set-top box associated with a particular subscriber is simpler because it involves only a single set-top box, at a fixed location. THE STRUCTURE OF THE INTERNET The Internet is made up of edge and backbone routers that direct traffic based on addresses contained within the headers of data packets. In an effort to reduce delays, Content Delivery Networks (CDNs) install servers at their own locations and that of the carrier's site at the 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 customers and to other routers. They are often located at Points of Presence (POPs) where multiple providers connect to the Internet. www.TechnicalPDF.com The edge of a network needs to support complex applications, protocols, and video. Edge routers must support multiple protocols, including Internet Protocol version 6 and version 4 (IPv6 and IPv4), Multi-Protocol Label Switching (MPLS), Wide Area Software Defined Networking (WA SDNs), and complex accounting software to track packet usage per customer. On MPLS networks, edge routers attach labels as described in Chapter 5, "Broadband Network 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. In addition, edge routers commonly handle aggregated Digital Subscriber Line Access Multiplexer (DSLAM) traffic in various formats; therefore, routers need to support both newer and older variations of IP and Wide Area Software Defined Networking (WA SDN). See Chapter 5 for a discussion of WA SDN. Edge routers also use addressing information to determine how to handle the data. See Figure 6-2 for an example of a router. www.TechnicalPDF.com Figure 6-2 An edge router programmed with the features listed above. These features are not present in backbone routers. (Courtesy of Ci