L6 LINK is a powerful proprietary connection developed by Line 6 to enable easy one-cable connectivity between a variety of Line 6 products. It passes both audio and control data via a single cable connection, and the resulting operation allows users to receive many incredible advantages. Currently POD HD300, HD400 and HD500 guitar multi-effect pedals, and DT50 amplifiers use L6 LINK.
L6 LINK uses a single XLR-type cable to send pristine digital audio in one direction (i.e. from a POD HD500 to a DT50) and control information in two directions (i.e. between a POD HD500 and a DT50). When you connect a POD HD multi-effect pedal to a DT50 guitar amplifier via L6 LINK, turning a tone knob on one will affect the tone of the other