pment must be selected and configured to support the level and type of traffic. For example, if the traffic is program content only, that's one set of circumstances. If the network is to carry voice, data, and provide Internet access, that's another. If the network is to carry multiple types of traffic, the equipment and facilities will have to be structured to accommodate it. Figure 3-3 shows a general reference architecture capable of sup- porting voice, data, Internet access, and content transport. Network Clock RJ 11/ 31/45 E1/T1 E3/DS3 802.xx VLAN - E3/DS3 Router 802.xx OC3/STM1 SMPTE Common Codec 802.xx Network Interface Equipment Station FIGURE 3-3 Premises Equipment Architecture 3 CONTENT TRANSPORT NETWORK DEFINED There are several characteristics of the architecture that should be pointed out and commented on. First, note the presence of a network clock reference and a separate station synchronizing refer- ence. Neither has anything to do with the other and that's the point. The network clock reference is to make sure the network is stable and jitter-free because it must carry the embedded program clock reference along with the content. After all, if the network isn't capable of carrying the program clock reference to a satis- factory degree of accuracy, then the content will suffer impair- ment. Although there appears to be a single-thread router and network interface, this is purely symbolic, and emblematic of the same level of redundancy as implied in the private branch exchange, LAN router, and Moving Picture Experts Group (MPEG) Codec. Resolving reliability, robustness and network performance concerns may re- quire redundant equipment and facilities, with emphasis on content value and specific traffic levels. The terms and symbols are generic and intentionally chosen to cover several alternatives without stating them implicitly. For example, any new facility design should take a serious look at voice-over IP telephone service. New installations or even replacement/upgrade installations, may find eco