Does the Multitech VoIP gateway mark the packets with Diffserv, or TOS?

Yes, Diffserv and TOS go hand-in-hand with the MultiVOIPs. We set the TOS bit to identify a packet as a voice packet when diffserv is enabled. A router that supports differentiated services (diffserv) will read this bit and identify the packet as a voice packet thereby giving it priority over data packets.

The TOS bit is set to 0x40 in hex or in binary 0100 0000.