In digital subscriber line (DSL) networks, a packet multiplexer that provides the interface between the DSL local loop and the service provider's point of presence (POP). Most DSLAMs are ATM-based, although some earlier models are based on frame relay, with the specific technology depending on what the carrier has in place. In an ADSL scenario the DSLAM receives upstream DSL traffic and splits, or demultiplexes, the voice and data traffic. The voice traffic then is encoded into pulse code modulation (PCM) format and time division multiplexed over a channelized T1,T3, or, perhaps, SONET link to the public switched telephone network (PSTN).The data traffic is multiplexed or concentrated in asynchronous transfer mode (ATM) cells over an unchannelized T1, T3, or SONET circuit directly to the Internet backbone, or to perhaps to an independent Internet service provider (ISP). The DSLAM generally represents the first potential point of contention and congestion that affects upstream end user traffic, as the local loop is a dedicated circuit. In asymmetric DSL (ADSL) implementations, the line side of the DSLAM in known as an ADSL transmission unit-centralized (ATU-C). See also ADSL, ATM, ATU-C, carrier, DSL, ISP, line side, PCM, POP, SONET, T1, T3, and upstream.