Local area network bridge
AssigneeInfotron Systems Corporation
InventorMario J. Leone
Life of this patent
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Abstract
In a bridge for interconnecting local area networks, the decision on whether or not to forward a frame is based on the frame's destination address. This is made possible in a practical bridge by a hardware-based prefilter which causes an abbreviated representation of the destination address of each frame to be generated, and uses the representation to address a global address table or "GAT" memory. Each cell of the GAT memory may correspond to more than one destination address. If any destination address, corresponding to the cell addressed by the prefilter, is active on a remote local area network, the prefilter allows the frame to be forwarded for further filtering by a software-controlled processor. Otherwise, the frame is discarded.
Claims17
In a data communications system in which communication takes place by the transmission of message frames, each frame including a destination address portion, the system comprising a first local area network interconnected with a network set, said set comprising at least one local area network, and all of the networks of said set being networks other than said first network, bridge means associated with said first local area network for interconnecting the first local area network with each local area network of said set and transmitting message frames, originating in said first local area network, from said first local area network to one or more of the local area networks of said set, said bridge means comprising:
- memory means storing data indicating whether each address in a set of addresses corresponds to a device active on a local area network of said network set;
- means responsive to the destination address portions of message frames originating in said first local area network for addressing said memory means;
- and
- means responsive to the addressed data in said memory means for preventing each frame originating in said first local area network from being transmitted to any of the networks of said network set when the destination address of said frame does not correspond to a device active on a network of said network set.
For use in a data communications network, a bridging device for interconnecting a first local area network with one or more other local networks through an interconnecting link comprising:
- memory means establishing a global address table containing memory cells, each cell having a unique address, each cell address representing at least one device address, and each cell having a first possible state representing that the device addresses to which it corresponds have not been sensed outside said first local area network and a second possible state representing that the device addresses to which it corresponds have been sensed outside said first local network, means for generating a representation of the destination address of each message frame transmitted in said first local area network, means for receiving said representation and using said representation to address the global address table, and means responsive to the state of each addressed memory cell in the global address table to prevent transmission of the frame through said interconnecting link if the addressed memory cell is in the first possible state.
For use in a data communications network, a bridging device for interconnecting a first local area network with one or more other local networks through an interconnecting link comprising:
- processing means for receiving and analyzing address portions of message frames transmitted by devices on said first local area network and for passing selected packets to the interconnecting link;
- memory means establishing a global address table containing memory cells, each cell having a unique address, each cell address representing at least one device address in accordance with a predetermined formula, and each cell having a first possible state representing that the device addresses to which it corresponds have not been sensed outside said first local area network and a second possible state representing that the device addresses to which it corresponds have been sensed outside said first local network, means for generating a representation of the destination address of each message frame transmitted in said first local area network using the same formula, means for receiving said representation and using said representation to address the global address table, and means responsive to the state of each addressed memory cell in the global address table to permit analysis of address information in said message frame by the processing means if the addressed memory cell is in said second possible state, and to prevent analysis of address information in said message frame by the processing means if the addressed memory cell is in the first possible state.
A method of selectively transmitting message frames from devices on a first local area network to devices on one or more other local area networks interconnected with said first network through a bridge, comprising the steps of:
- determining, by filtering means in said bridge, whether destination address portions of frames generated in said first network do not correspond to addresses of devices on said other networks;
- and
- discarding, in said bridge, frames the destination address portions of which have no corresponding device addresses on said other networks.
Dependencies are inferred from the claim text.