n place. How deep into the network should fiber be placed, and what will be the cost of replacing existing copper with fiber? The main architectural difference between major service providers is how far to drive the fiber toward the home. As described in the following sections, there are two main FTTx options: FTTN-FTTN uses a variety of DSL technologies to optimize the copper bandwidth. When extending FTTN, the network takes advantage of exist- ing copper or HFC plants to deliver services. FTTH/FTTP-This approach is being used today by MSOs. The biggest benefit of FTTN is that it takes advantage of the enormous amount of existing copper. The most important challenge-and disadvantage-is to squeeze sufficient capacity out of that plant to deliver triple-play services (voice, data, and video services) or, more specifically, video. In order to accommodate more bits per second down the transmission path, two techniques must be applied: Increase the usable bandwidth (i.e., provide a bigger frequency band), and strive to get greater Chapter 12 Broadband Access Alternatives bandwidth efficiency by enhancing the signal encoding, or modulation, technique (i.e., carry more bits per second per Hertz). In the FTTN architecture, the fiber is extended to the serving area interface- that is, the point at which the telco's feeder cable connects to the local distribution cable (see Figure 12.6). The intended range of the copper connection is 1 mile (1.5 km), with the goal of delivering 25Mbps over that range. Two alternatives can be used to achieve this objective: bonded ADSL2+ and VDSL. Given the 20Mbps to 30Mbps local connection supported by FTTN, not many digital video channels can be accommodated. Video over FTTN will require a new architecture to deliver high-quality multimedia content over a limited-capacity copper loop. In response to this challenge, the telcos are investigating the use of a packet-based architecture for video. Two IP video proposals are being considered at this time. One solution for packet-based video is