 capable of supporting DSL transmission. As a brief refresher, the DLC RT multiplexer uses fixed 64-kbit/s time slots for each subscriber as it was developed during an era prior to emergence of the need for broadband communications. Now that the need for subscribers to transmit data beyond the 64-kbit/s capacity of the time slot allocated to each subscriber has arisen, the DLC RT is becoming obsolete. Options For the reasons mentioned above, many telephone companies are installing fiber from their central offices to neighborhoods. At those neighborhood locations a splitter can be used on each twisted-pair ter- mination to separate voice and data channels. Voice can be amplified and placed back into existing copper bundles or the DLC RT infrastruc- ture, while DSL modem data can be aggregated via the use of a digital subscriber line access multiplexer (DSLAM) for transmission via a fiber- optic cable to the central office, where it again bypasses the normal voice network. Another option being used by some telephone companies involves replacing their existing copper links into a neighborhood with optical fiber that is then used for both voice and data communications. In this networking environment a multiplexer is used to digitize each voice channel and to aggregate both voice and data from subscribers for trans- mission to the central office, where voice and data are separated from one another. Figure 7.7 illustrates one example of the emerging telephone company wiring infrastructure. In this example the multiplexers located within each neighborhood are shown supporting both voice and data from the neighborhood to the central office. In examining Figure 7.7, note that the fiber trunk replaces a relatively long "backhaul" use of twisted-pair copper wire. Because DSL operations Chapter Seven Figure 7.7 fiber trunk An example of the emerging telephone Central Office company wiring infrastructure that uses fiber to the fiber trunk neighborhood. Legend: Subscriber Multiplexer Electrical to optical converter are distanc