Cabletron Systems DLE52-MA User Manual page 18

Chapter 1: Virtual Local Area Networks
a 1Q Trunk port has all VLANs in its Port VLAN List and is configured to
transmit all frames as tagged frames. A 1Q Trunk drops all incoming
frames that do not have a VLAN tag.
1D Trunk
A connection from a switch that passes only untagged traffic. By default,
a port designated as a 1D Trunk port has all VLANs on its Port VLAN
List and is configured to transmit all frames as untagged frames.
1-6 802.1Q VLAN User's Guide