Patent ID: 7710985

Claim:
A bridged LAN comprising: a transit network in which a plurality of Virtual LANs (VLANs) are formed; and a plurality of local area networks (LANs) connected to the transit network in which a logical spanning tree is formed for each of Multiple Spanning Tree Protocol (MST) instances composed of one or more of VLANs, the transit network being composed of a plurality of bridges for transmitting and receiving Ethernet frames, each of said bridges having: a conversion table defining an identifier of each of the MST instances in association with a combination of a VLAN identifier and a value of a Class of Service (COS); and means for forming in said transit network the spanning tree for each of the MST instance identifiers defined in the conversion table; a specified one of said plurality of VLANs comprising: a session management server belonging to a first LAN; and a plurality of second LANs each including at least one client terminal; wherein each of said bridges extracts a VLAN identifier and a COS value from a header of a received frame, specifies the MST instance identifier of the received frame in accordance with said conversion table, and forwards the received frame in accordance with a route of the spanning tree having the MST instance identifier, and wherein a spanning tree having the MST instance identifier associated with the combination of the identifier of the specified VLAN and the COS value allocated for voice communication is formed so as to minimize a frame forwarding delay between said first LAN and each of said second LANs.