Browse Prior Art Database

Local Area Network Switch Frame Lookup Technique for Increased Speed and Flexibility

IP.com Disclosure Number: IPCOM000115937D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 78K

Publishing Venue

IBM

Related People

Allemang, MD: AUTHOR [+6]

Abstract

Disclosed is an incoming frame lookup method that can be used in Local Area Network (LAN) switches and workgroup concentrators. This scheme allows a rapid, flexible Source Address (SA) lookup for detection of station changes and maintenance of port configuration data. Future network enhancements such as Virtual LANS (VLANs) and roving stations are supported by the disclosed method.

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This is the abbreviated version, containing approximately 52% of the total text.

Local Area Network Switch Frame Lookup Technique for Increased Speed
and Flexibility

      Disclosed is an incoming frame lookup method that can be used
in Local Area Network (LAN) switches and workgroup concentrators.
This scheme allows a rapid, flexible Source Address (SA) lookup for
detection of station changes and maintenance of port configuration
data.  Future network enhancements such as Virtual LANS (VLANs) and
roving stations are supported by the disclosed method.

      The solution described is typically applied in a LAN switch
design similar to the one shown in Fig. 1.  Note that the incoming
frame lookup logic is capable of processing more than a single
downstream port.  It is also significant that the frame lookup logic
is contained entirely within a generic frame processor chip.  This
eliminates the need for an expensive and relatively slow external
lookup memory or CAM module.

      Each downstream port is configured with certain characteristics
that effect how the switch reacts to an incoming frame during lookup.
This is combined with a fast, compact compare scheme that can be
implemented in a single chip for cost savings.  In some cases, frame
processing is performed immediately in the lookup logic, while in
others the data is tagged with appropriate information and sent to
the switch fabric for processing.

The defined port information allows the following cases to be
handled:
  1.  Always forward the frame, even if the SA is unexpected (for
       shared ports),
  2.  If an expected SA then forward, otherwise notify the
       microprocessor to l earn the new SA (...