It is a digital audio signal which is defined by AES 3 standard (this signal is called AES EBU signal or digital audio signal as well). This standard defines a digital audio format used by professional audio systems.
Cables and connectors: Standard says a balanced (1) and shielded cable with a characteristic impedance of 110 ohm with XLR-3 connectors (2). Unshielded or shielded strutured wiring can be used as well. Peak-to-peak levels are between 2 Vpp and 7Vpp in a 110 ohm impedance. A typical value is 4 V ± 10%. AES3id (3) standard transmit AES3 signal through coaxial cable.