A two-wire line (2Dr) is a copper twisted pair (CuDa) in which the two wires are twisted together. this line forms the most common connection from the junction box to the local exchange
. The two wires of the two-wire line are designated with the letters a and b and therefore represent the a/b interface
. Thetwo-wire line is normally assumed to be a telephone
cablecorresponding to cable quality category
1 for voice transmissions. As a rule, higher-quality two-wire lines for LAN applications are referred to as twisted pair cables or TP cables.