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Browse Prior Art Database

In-Order Frame Delivery in a Connectionless Switching Fabric

IP.com Disclosure Number: IPCOM000112195D
Original Publication Date: 1994-Apr-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 4 page(s) / 187K

Publishing Venue

IBM

Related People

Georgiou, CJ: AUTHOR [+3]

Abstract

Connectionless switch fabrics, such as that for the ANSI Fibre Channel Standard, do not guarantee in-order frame delivery. In a high-bandwidth environment, reordering frames which were misordered by the fabric degrades performance at the receiving unit. Disclosed is a method of creating, maintaining, and removing implicit virtual circuits which enables related frames to be sent through the fabric in the order transmitted.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 29% of the total text.

In-Order Frame Delivery in a Connectionless Switching Fabric

      Connectionless switch fabrics, such as that for the ANSI Fibre
Channel Standard, do not guarantee in-order frame delivery.  In a
high-bandwidth environment, reordering frames which were misordered
by the fabric degrades performance at the receiving unit.  Disclosed
is a method of creating, maintaining, and removing implicit virtual
circuits which enables related frames to be sent through the fabric
in the order transmitted.

      The invention pertains to a system consisting of a set of nodes
which communicate by means of a fabric of multiple interconnected
switches.  The invention is applicable to an architecture in which
the transmitted data are organized as groups of logically related
frames which we call sequences.  An example of such an architecture
is the proposed ANSI Fibre Channel Standard (FCS).  In particular,
the invention is applicable to the connectionless operating modes of
such an architecture.

      Since the virtual circuit is implicit, it requires no action on
the part of the communicating nodes to create it.  It thus eliminates
the overhead of the extra communication normally required to request
the fabric to create a virtual circuit.  It does not require the
communicating units to remember a virtual circuit identifier in
addition to their addresses.  The invention is particularly suited to
a network of switches in which each switch controls its own routing
without communicating with other switches, since the invention
requires no global information or inter-switch communication to
create, maintain, and remove virtual circuits.

      A temporary virtual circuit is created, if a suitable one does
not already exist, when a node starts sending a sequence and is
removed at the end of the sequence or at the end of a series of
sequences to the same destination which are either multiplexed or
separated by short idle periods.  A "continue-sequence"  field in the
frame header indicates whether or not the sender will be sending
another related sequence in a short time.  The information for
identifying and managing the virtual circuits is maintained
separately by each switch port for sequences which it is receiving
from the directly attached node or switch.

      A virtual circuit can be identified by the source and
destination node addresses (S_ID and D_ID) in the frames, as is known
in the art.  The reason for needing both the S_ID and D_ID is that in
the interior of the fabric, traffic for multiple node pairs might
take the same link but should still be on separate virtual circuits
to ensure maximum use of all available links through the fabric.
However, this does mean that matching a received frame to its virtual
circuit involves looking up a 6-byte circuit ID (assuming that S_ID
and D_ID are each 3 bytes) in order to find the correct outgoing
port.  In this invention, it is not necessary for the switch to
include the D_ID in t...