TP-Link T1600G-18TS Configuration Manual page 486

Configuring Voice VLAN Overview
 OUI Address (Organizationally Unique Identifier Address)
The OUI address is used by the switch to determine whether a packet is a voice packet.
An OUI address is the first 24 bits of a MAC address, and is assigned as a unique identifier
by IEEE (Institute of Electrical and Electronics Engineers) to a device vendor. If the source
MAC address of a packet complies with the OUI addresses in the switch, the switch
identifies the packet as a voice packet and prioritizes it in transmission.
Configuration Guide 463