3Com PathBuilder S200 Series Owner's Manual page 24

Setting Up WAN Operation for Bridging
LAN Connection
Subaddress
20
The LAN Connection Subaddresses identifies all LAN Connections. Incoming calls
with a network address consisting of the Node Address specified in the Node record
and the LAN Connection Subaddress, specified in the LAN Connection Table, are
verified and allowed to connect to the WAN Adapter in order to reach the LAN
bridges.
The LAN Connection Subaddress is appended to the calling address of the Call
Request packet if generated and sent by the WAN Adapter. Use the default value
unless it conflicts with an address already in use.
Refer to the "LAN Connection Table" section on page 31 for more details.
Bridging