Method and apparatus for hardware forwarding of LAN frames over ATM networks

Abstract

A multiported LAN switch comprised of legacy local area network ports and ATM ports. Each ATM port comprising a hardware forwarding engine for bridging LAN frames from the LAN ports to the ATM port. The hardware forwarding engine converts layer 2 protocols between the dissimilar ports expediently, without requiring intervention by a microprocessor. A substantial performance gain is attained compared to microprocessor controlled format converters. Both LAN emulation and virtual LANs are supported.

What is claimed is:  
     
         1 . A local area network (LAN) switching apparatus for interconnecting a LAN segment to an Asynchronous Transfer Mode (ATM) network, comprising: 
 a plurality of LAN ports, wherein each LAN port connects one unique LAN segment to a LAN switch;    at least one ATM port, wherein each ATM port of the LAN switch interfaces to the ATM network;    a connection means for establishing a plurality of connection paths simultaneously, wherein each said connection path establishes a connection through the switching apparatus between any two or more of the plurality of LAN ports and ATM ports, said connection path for transmitting data comprising LAN frames;    a data transmission means for formatting data for transmission over said LAN into standard LAN frames in compliance with the international standard of Open Systems Interconnection (OSI), wherein said standard provides a universally applicable layered architecture containing seven layers, numbered from 1 to 7, with each layer having a set of defined functions and providing a set of services to and from the adjacent two layers; and    a LAN to ATM format conversion means for changing the format of data as it traverses the LAN switch from LAN port to switch to ATM port, wherein LAN frames are converted to switch frames for transfer through the switching apparatus and switch frames are converted to ATM frames in preparation for transfer to the ATM network;    an ATM adapting apparatus for converting ATM frames to ATM network format and ATM network format to ATM frames, wherein ATM network format comprises segmenting said ATM frame into sequential ATM cells comprising 5 bytes of header and 48 bytes of data; and    a first multiprotocol processing means, wherein said LAN switch converts either layer 2 or layer 3 of the OSI standard from LAN frames to switch frames to ATM frames, wherein LAN frames are compatible with LAN protocol and ATM frames are compatible with the first ATM adapting apparatus protocol.    
     
     
         2 . The LAN switching apparatus of  claim 1  further comprising: 
 an ATM to LAN format conversion means for changing the format of data as it traverses the LAN switch from ATM port to switch to LAN port, wherein ATM frames are converted to switch frames for transfer through the switching apparatus and switch frames are converted to LAN frames for transfer to the LAN port; and  
 a second multiprotocol processing means, wherein the LAN switch converts either the layer 2 or layer 3 of the OSI standard from ATM frames to switch frames to LAN frames.  
 
     
     
         3 . The LAN switching apparatus of  claim 2 , further comprising a sorting means for the ATM port, wherein the ATM port sorts LAN frames arriving from said switch connection path and ATM frames arriving from the ATM network into three categories, comprising: 
 a first category of frames for routing, wherein layer 3 of the OSI standard is converted from LAN frames to ATM frames, or layer 3 of the OSI standard is converted from ATM frame format to LAN frame format;    a second category of frames for bridging, wherein layer 2 of the OSI standard is converted from LAN frame format to ATM frame format or layer 2 of the OSI standard is converted from ATM frame format to LAN frame format; and    a third category of frames for aborting, wherein LAN frames or ATM frames are erroneous and cannot be routed or bridged.    
     
     
         4 . The LAN switching apparatus of  claim 3  wherein the ATM port further comprises a hardware forwarding means for bridging frames from switch frame format to ATM frame format, or from ATM frame format to switch frame format, said bridging without requiring processor intervention.  
     
     
         5 . The LAN switching apparatus of  claim 4  wherein the ATM port further comprises a routing processor means for routing switch frames and routing ATM frames under software control.  
     
     
         6 . The LAN switching apparatus of  claim 5  wherein the sorting means further comprises a single ported frame memory comprising: 
 a hardware transmit queue for temporarily storing switch frames in transit between the switch and the ATM adapting apparatus for subsequent accessing by the hardware forwarding means for bridging switch frames to ATM frames;  
 a software transmit queue for temporarily storing switch frames in transit between the switch and the ATM adapting apparatus for subsequent accessing by the routing processor means for routing under software control switch frames to ATM frames;  
 a hardware receive queue for temporarily storing ATM frames in transit between the ATM adapting apparatus and the switch for subsequent accessing by the hardware forwarding means for bridging ATM frames to switch frames;  
 a software receive queue for temporarily storing ATM frames in transit between the ATM adapting apparatus and the switch for subsequent accessing by the routing processor means for routing under software control ATM frames to switch frames; and  
 a set of conversion tables for assisting the hardware forwarding means for converting switch frames to ATM frames and ATM frames to switch frames.  
 
     
     
         7 . The LAN switching apparatus of  claim 6  wherein the sorting means operates such that frames of the first category are stored to the software transmit queue, frames of the second category are stored to the hardware transmit queue, and frames of the third category are discarded.  
     
     
         8 . The LAN switching apparatus of  claim 7  wherein the hardware forwarding means further comprises an ATM formatting means for generating an ATM frame format, comprising the LAN frame prefixed with an ATM control header, the ATM control header comprising: 
 a virtual channel connection field for defining the connection route through the ATM network; and  
 a LAN emulation header for identify unique LAN frames for carrying control information.  
 
     
     
         9 . The LAN hardware switching apparatus of  claim 8  wherein the hardware forwarding means further comprises a LAN formatting means for generating a switch frame format, comprising the LAN frame prefixed with a switch header, the switch header comprising: 
 a tag field for specifying the address of the conversion table entry for access by the hardware forwarding means from the frame memory to obtain the conversion parameters to ATM frame format, comprising the virtual channel connection field and the LAN emulation header;  
 a frame type field for characteristics of the switch frame, and an exit port definition field for defining to the connection means which switch port is the destination of the switch frame.  
 
     
     
         10 . The LAN switching apparatus of  claim 9  wherein the hardware forwarding means further comprises a hardware format converter for converting switch frames to ATM frames by replacing the switch header with the ATM control header.  
     
     
         11 . The LAN switching apparatus of  claim 10  wherein the hardware forwarding means addresses the conversion tables in frame memory using the tag field of the switch header to access the ATM control header, whereupon the switch header is destroyed and the ATM control header is accessed from the conversion tables and prefixed to the LAN frame.  
     
     
         12 . The LAN switching apparatus of  claim 11 , further comprising an ATM memory queuing means, wherein ATM frames are temporarily stored before being segmented and transmitted to the ATM network or after being received and reassembled from the ATM network.  
     
     
         13 . The LAN switching apparatus of  claim 9  wherein the hardware forwarding means further comprises ATM enqueuing means, wherein the ATM enqueuing means requests a queue from ATM memory queuing means, when the request is granted, sends the ATM frame to ATM memory queuing means from the hardware transmit queue in frame memory, erases the ATM frame from hardware transmit queue, and signals ATM adapting apparatus to segment and transmit the ATM frame.  
     
     
         14 . The LAN switching apparatus of  claim 13  wherein the sorting means further comprises an exit port destination field of the switch header including a first binary bit value for defining frames to be routed and a second binary bit value for defining frames to be bridged.  
     
     
         15 . The LAN switching apparatus of  claim 14  wherein the sorting means sorts frames such that frames of the first category are stored to the software receive queue, frames of the second category are stored to the hardware receive queue, and frames of the third category are discarded.  
     
     
         16 . The LAN switching apparatus of  claim 15  wherein the hardware forwarding means further comprises a virtual LAN number for identifying the ATM frame, wherein the virtual channel connection field of the ATM control header is used to address the conversion tables and access a virtual LAN number.  
     
     
         17 . The LAN switching apparatus of  claim 16  wherein the hardware forwarding means further comprises a virtual LAN filtering means for determining whether the ATM frame arriving from the ATM network is to be bridged to the LAN or discarded.  
     
     
         18 . The LAN switching apparatus of  claim 17  wherein the virtual LAN number and Destination MAC Address of the ATM frame is used to address the conversion tables and access a valid or invalid destination switch header, wherein frames having a valid destination switch header are bridged and frames not having a valid destination switch header are discarded.  
     
     
         19 . The LAN switching apparatus of  claim 18  wherein the hardware forwarding means further comprises an ATM to switch conversion means for converting ATM frames to switch frames by replacing the ATM control header with the switch header.  
     
     
         20 . The LAN switching apparatus of  claim 19  wherein the said ATM control header is destroyed and the switch header is generated from the valid switch destination address and frame type field accessed from conversion tables and the switch header is prefixed to the LAN frame.  
     
     
         21 . The LAN switching apparatus of  claim 20  wherein the virtual channel connection field of the ATM control header includes a first binary value for defining frames to be routed and a second binary value for defining frames to be bridged.  
     
     
         22 . A format converter comprised only of hardware for bridging frames from a first frame format to a second frame format, said bridging without requiring processor intervention.  
     
     
         23 . A message frame sorter for sorting first type and second type frames based on destination address to a first queue and a second queue, wherein first types frames are stored in said first queue and second type frames are stored in said second queue.  
     
     
         24 . A bridging apparatus comprised only of hardware for converting and forwarding frames having a first frame format to frames having a second frame format, said conversion without requiring processor intervention.  
     
     
         25 . The bridging apparatus of  claim 24 , further comprised of conversion tables for assisting in said converting and forwarding of frames.  
     
     
         26 . A protocol adaption apparatus comprised only of hardware for converting and forwarding frames having a first protocol to frames having a second protocol, said conversion without requiring processor intervention.  
     
     
         27 . A LAN emulation system comprising: 
 a plurality a local area networks (LANs);    an ATM network;    a plurality of LAN switches for interconnecting LANs and ATM networks;    a controlling processor; and    a LAN emulation means, wherein communications in the form of frames are transmitted from a first LAN to the LAN switch to the ATM network to the LAN switch to a second LAN.    
     
     
         28 . The LAN emulation system of  claim 27  wherein the LAN emulation means further comprises LAN emulation control hardware for presetting LAN switch controls in advance of the frame transmission for controlling the ATM network to function like a LAN when transporting frames from LANs to ATM or ATM to LANs.  
     
     
         29 . The LAN emulation system of  claim 28  wherein the LAN emulation means further comprises a LAN emulation header means for identifying frames having information for presetting the LAN emulation control hardware.  
     
     
         30 . The LAN emulation system of  claim 29  wherein the LAN emulation control hardware further comprises a plurality of registers for storing LAN emulation headers, wherein each register contains a unique LAN emulation header data pattern.  
     
     
         31 . The LAN emulation system of  claim 30  wherein the plurality of registers specify the set of LAN emulation headers that contain information for presetting the LAN emulation control hardware.  
     
     
         32 . The LAN emulation system of  claim 30  wherein the LAN emulation means further comprises a LAN emulation control sorting means for checking each LAN emulation header arriving from the ATM network to determine if the LAN emulation header matches any of the prestored plurality of LAN emulation headers in the registers and contains information for presetting the LAN emulation control hardware.  
     
     
         33 . The LAN emulation system of  claim 32  wherein the LAN emulation means further comprises a forwarding means, wherein frames arriving from the ATM network containing information for presetting the LAN emulation control hardware are sent to the controlling processor to be processed.