telli- gence mentioned earlier in terms of compression and error control features. Because of the dynamic allocation of time slots, a stat mux can carry two to five times more traffic than a traditional time division mux. But, again, as you load the stat mux with traffic, you run the risk of delays and data loss. Stat muxes are extremely important because they are the basis on which packet-switching technologies (e.g., X.25, IP, Frame Relay, ATM) are built. The main benefit of a stat mux is the efficient use of bandwidth, which leads to transmission efficiencies. Intelligent Multiplexing An intelligent multiplexer is often referred to as a concentrator, particularly in the telecom world. Intelligent muxes are not used in pairs; they are used alone. An intelligent mux is a line-sharing device whose purpose is to concentrate large num- bers of low-speed lines to be carried over a high-speed line to a further point in the network. A good example of a concentrator is in a device called the digital loop carrier (DLC), which is also referred to as a remote concentrator or remote terminal. In Fig- ure 1.17, twisted-pairs go from the local exchange to the neighborhood. Before the Multiplexing Local Exchange Distribution Switch System (cross-connect) Two copper pairs can carry Concentrator 24 (T-1) or 32 (E-1) channels Digital Loop Carrier Figure 1.17 Intelligent multiplexing: concentrators advent of DLCs, each household needed a twisted-pair. If the demand increased beyond the number of pairs available for that local exchange, the users were out of luck until a new local exchange was added. Digital technology makes better use of the existing pairs than does analog. Instead of using each pair individually per subscriber from the local exchange to the subscriber, you can put a DLC in the center. A series of either fiber-optic pairs or microwave beams connects the local exchange to this intermediate DLC, and those facilities then carry multiplexed traffic. When you get to the DLC, you break out the individual twisted-pairs 