Apparatus for and method of flow switching in a data communications network

A method of switching data utilizing tags for use in a network device, said method comprising the steps of:

• providing a first cache for storing previously received flows and tags corresponding thereto;
• identifying flows on an input port of said network device by comparing the flow corresponding to a received frame with the flows of a limited number of recently received flumes received by said input port;
• searching for a matching flow in a said first cache and reading the tag corresponding thereto in the event of a cache hit, and randomly assigning a tag from a pool of unused tags and storing said tag and corresponding flow in said first cache in the event of a cache miss;
• in the event unused tags are available, selecting a tag for reuse and setting a new-tag-bit in the received frame only for the first fame of said flow:
• appending said tag to said received frame;
• providing a second cache for storing forwarding decisions and corresponding tags;
• for each new flow received, calculating a forwarding decision for the flow, and storing the results of said forwarding decision and the tag associated therewith in said second cache;
• for frames of a flow other than the first, retrieving a forwarding decision from said second cache based on the tag appended to said received frame;
• and
• forwarding the data frame to the appropriate output port in accordance with the forwarding decision corresponding thereto.

A tag switching apparatus for use in a network device, comprising:

• an I/O processor comprising a plurality of input ports, each input port comprising:
• a first cache for storing tags and flows associated therewith;
• a tag processor adapted to:
• determine a current flow from a header portion of a received frame and compare said current flow with recently received flows stored in said tag assignment cache;
• if a match is found, reading a tag from said tag assignment cache corresponding to said current flow;
• if a match is not found randomly choosing a tag from a pool of unused taps and associating it with said current flow and storing said current flow and said tag in said tag assignment cache;
• in the event no unused tags are available, selecting a tag for reuse and setting a new-tag-bit in the received frame only for the first frame of said current flow;
• appending said tag to the received frame;
• a controller comprising:
• a second cache for storing forwarding decisions and corresponding tags;
• a forwarding decision associated with a tag upon a miss in;
• a header processor adapted to:
• for each new flow received, calculate a forwarding decision for the flow associated with a tag and store the results of said forwarding decision and the tag associated therewith in said send cache, said header processor adapted;
• and
• for frames of a flow other than the first, retrieve a forwarding decision from said second cache based on the tag appended to said received frame.