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Embedded Check Generation for Label Swapping

IP.com Disclosure Number: IPCOM000107513D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 5 page(s) / 183K

Publishing Venue

IBM

Related People

Bond, AL: AUTHOR [+2]

Abstract

In a packet network utilizing transparent routing, the check field in the routing header must be recalculated after every hop or path juncture since the label field is replaced. The check field in the packet routing header is necessary to insure data integrity and avoid mis- routes due to communication line disturbances which may modify the address and control fields causing loss or other link congestion.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 43% of the total text.

Embedded Check Generation for Label Swapping

       In a packet network utilizing transparent routing, the
check field in the routing header must be recalculated after every
hop or path juncture since the label field is replaced.  The check
field in the packet routing header is necessary to insure data
integrity and avoid mis- routes due to communication line
disturbances which may modify the address and control fields causing
loss or other link congestion.

      This invention defines a method and logic structure for check
field creation in a label swapping (transparent mode) packet routing
system which eliminates the need for complex in-line high speed
logic.  The idea is to pre-calculate and store the delta check field
of the packet route header so that a single logical transformation
can be performed on the original (receiving) check field when the
address (label) is swapped.

      In label swap routing network, the label is replaced at every
link's receiver with a new label and transmitted to the next
receiver, the notion being, to use the received label as an address
or index into a table for retrieving the next label "address".  This
is typically accomplished by utilizing an array (memory device).

      The objective is to perform this quickly and simply so that the
throughput of the fast packet network is not reduced or constrained
by hardware or software actions.  To accomplish this, knowing that
the label is actually an index into a table "memory", the check
field, associated with the label, is calculated at the time of table
entry creation or connection establishment (defining the hop path
through the network).  That is, since the receive label (old label)
is known to be an address for a memory entry in memory, and the
transmit label (new label) is known based on the route being defined,
the memory address and entry can be combined (subtract and add) to
generate the delta for the packet header check field.  The check
field is a mathematical algorithm which would include all fields of
the transparent routing header.  The header is typically more than
just the label and check field, but will include such items as
control and type identifiers.

      In the most general case, a receive packet is checked and the
old label is extracted from the route header.  The old label is used
as an address to access the table for the new label including the
pre-calculated delta check field. The newly read label is placed back
into the packet, replacing the old label used for addressing.  Now,
the pre- calculated check field is combined with the receive header
check field to produce the new/correct check field for the transmit
header (see Fig. 1). The old label (address) in the receive route
header is shown as 2 bytes but could be many bytes or as little as
a few bits.  Similarly, the array table could contain an equal number
of bytes as the old label header or many more bytes.  These bytes
could be used for other...