An apparatus and method of using same for associating a tag with each
packet in an ATM switch to eliminate the need for an OVC table, thus
saving both egress processing time and memory resources. The tag includes
both a type of switching identifier and a per-logical-interface or
per-external-VC information field. A packet received by the egress packet
processing engine has associated with it (by the control plane) a frame
control word containing a new cell header (NCH) corresponding to the OVC
on which the packet was received from the fabric. This NCH contains the
tag used to expedite egress processing. In one embodiment of the present
invention, the tag value is provided in two fields, a tag type and a tag
parameter. The tag type represents a code for different data path
applications. The tag parameter takes on multiple values based on the tag
type. The present invention efficiently uses the OVC to NCH mapping to
map many OVCs to a small set of tags coded within the switch's NCH so
that, rather than having to do an extra look-up in the egress engine in a
large and non-scaleable OVC table, the egress engine has only to look in
a small, fully-scaleable tag table. In fact, in one embodiment, no egress
look-up is required at all.