Also known as Single-line DSL. An umbrella term for nonstandard variations of high-bit-rate digital subscriber line (HDSL) operating over a single unshielded twisted pair (UTP). SDSL uses the same 2B1Q line coding as HDSL, and runs at rates from 128 kbps to 2.32 Mbps.Typical signaling rates are 400 kbps for local loops of up to 18,000 feet in length, and 784 kbps for loops up to 12,000 feet. At those signaling rates, SDSL yields a payload transmission rates of 384 kbps and 768 kbps, respectively. See also 2B1Q, HDSL, HDSL2, HDSL4, payload, signaling rate, transmission rate, and UTP.