Browse Prior Art Database

Relative Rate Marking Method for Asynchronous Transfer Mode Available Bit Rate Switches

IP.com Disclosure Number: IPCOM000117653D
Original Publication Date: 1996-Apr-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 88K

Publishing Venue

IBM

Related People

Kunzinger, CA: AUTHOR

Abstract

Disclosed is a feedback generation method for use in Asynchronous Transfer Mode (ATM) Available Bit Rate (ABR) switches that support Relative Rate (RR) marking but do not support Explicit Rate (ER) marking. The method mitigates several known problem areas in management and allocation of available bandwidth to ABR end systems, such as ACR retention, ACR promotion, and ACR reclamation. It also provides timely and fair allocation of the available transmission capacity across a set of ABR connections with minimal computational burden for relative rate marking switch.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Relative Rate Marking Method for Asynchronous Transfer Mode Available
Bit Rate Switches

      Disclosed is a feedback generation method for use in
Asynchronous Transfer Mode (ATM) Available Bit Rate (ABR) switches
that support Relative Rate (RR) marking but do not support Explicit
Rate (ER) marking.  The method mitigates several known problem areas
in management and allocation of available bandwidth to ABR end
systems, such as ACR retention, ACR promotion, and ACR reclamation.
It also provides timely and fair allocation of the available
transmission capacity across a set of ABR connections with minimal
computational burden for relative rate marking switch.

      An ABR relative rate switch uses the target occupancy of the
ABR buffer, "r", the actual occupancy of the ABR buffer, &rho., and
the number of forward RM-cells received in an observation interval to
generate feedback to active ABR sources by means of the <CI, NI> bits
of an RM-cell.  Only one instance of rate-increasing feedback is
allowed for a given ABR connection within an interval T(comp).

      The RR-switch also maintains a second timer of longer duration,
T(reclm), that will be used to trigger a "bandwidth reclamation"
phase, wherein the switch will spontaneously generate backward
RM-cells to be sent to those sources who have not transmitted at
least one forward RM-cell during the interval, instructing inactive
and lazy sources to reduce their accumulated ACR value.

      Time interval T(comp) will be much smaller than interval
T(reclm): typically, T(comp) will be on the order of the nominal
roundtrip delay of the ABR control loop (e.g., tens to hundreds of
microseconds), while T(reclm) will be on the order of hundreds of
milliseconds.

The switch maintains a table with the following information for each
ABR connection:
  o  A connection identifier
  o  RM(comp): A one bit flag to indicate if a forward RM-cell has
      been received by the switch witihin the current T(comp)
interval
  o  RM(reclm): A one bit flag to indicate if a forward RM-cell has
      been received by the switch within the current T(reclm)
interval.

      The switch will allow all active ABR sources to increase their
ACR values whenever the local buffer occupancy, &rho., is less than
the target occupancy, r.

The following switch behavior encompasses both rate-increase and
rate-decrease feedback to actively transmitting ABR sources:
  1.  At the start o...