ADSL links run across twisted-pair telephone wires. When ADSL modems are connected to each end of a telephone wire, a dual-purpose ADSL circuit can be created. Once established, the circuit can transmit lower-frequency voice traffic and higher-frequency data traffic.
To accommodate both types of traffic, ADSL modems are connected to plain old telephone service (POTS) splitters that filter out the lower-bandwidth voice traffic and the higher-bandwidth data traffic. The voice traffic can be directed as normal telephone voice traffic. The data traffic is directed to the ADSL modem, which is typically connected to the data network.
Because twisted-pair wiring has a length limit, ADSL modems are typically connected to multiplexing devices. DSL access multiplexers (DSLAMs) can process and route traffic from multiple splitters. This typical ADSL configuration is shown in Figure 6.
Figure 6: Typical ADSL Topology
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