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Integrated Binary/Explicit Rate Marking Method for Asynchronous Transfer Mode Available Bit Rate Switches

IP.com Disclosure Number: IPCOM000117572D
Original Publication Date: 1996-Apr-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 102K

Publishing Venue

IBM

Related People

Kunzinger, CA: AUTHOR

Abstract

The Asynchronous Transfer Mode (ATM) Forum's Traffic Management specification of Available Bit Rate (ABR) service requires a switch to support at least one of three feedback methods. Simultaneous support of multiple methods is permitted, but is neither defined nor constrained by the service specifications. Disclosed is an ABR feedback generation method for use in ABR switches that will incorporate Relative Rate (RR) marking and Explicit Rate (ER) marking in an integrated fashion. Integrated feedback methods allows an ABR switch to mitigate several known problem areas in management and allocation of available bandwidth to ABR end systems: namely, ACR retention, ACR promotion, and ACR reclamation.

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Integrated Binary/Explicit Rate Marking Method for Asynchronous Transfer
Mode Available Bit Rate Switches

      The Asynchronous Transfer Mode (ATM) Forum's Traffic Management
specification of Available Bit Rate (ABR) service requires a switch
to support at least one of three feedback methods.  Simultaneous
support of multiple methods is permitted, but is neither defined nor
constrained by the service specifications.  Disclosed is an ABR
feedback generation method for use in ABR switches that will
incorporate Relative Rate (RR) marking and Explicit Rate (ER) marking
in an integrated fashion.  Integrated feedback methods allows an ABR
switch to mitigate several known problem areas in management and
allocation of available bandwidth to ABR end systems:  namely, ACR
retention, ACR promotion, and ACR reclamation.  The method provides
timely and fair allocation of the available transmission capacity
across a set of ABR connections while minimizing the associated
computational burden and providing improved bandwidth utilization in
comparison to use of only a single marking method within a switch.

      The integrated feedback method uses either RR-marking or
ER-marking, based on a target occupancy for the ABR buffer, "r", and
its actual occupancy of the ABR buffer, &rho.:
  1.  When the ABR buffer occupancy is low (&rho.<r), the switch will
       provide: hp1.selective explicit rate feedback via the ER field
       to allow increases in ACR.  This will allow the actively
       transmitting sources to undertake reasonably aggressive
additive
       rate increases.
  2.  When the ABR buffer occupancy is high (&rho.>=r), the switch
will
    provide global relative rate feedback using the <CI, NI> bits,
    instructing sources to reduce their Allowed Cell Rate (ACR)
    values.

      The ABR switch uses current information from an active
connection's forward RM-cells ("upstream" ER value, current CCR
value, current "NI" bit, and current "CI" bit) as input to the
switch's Explicit Rate algorithm.  The switch also maintains state
information for each ABR connection that it serves, namely:
  o  the connection ID,
  o  the last Explicit Rate advertised to the source by this switch,
  o  a flag to indicate if a forward RM-cell has been received from
      the source since the last fedback RM-cell, either forward or
      backward, was transmitted by the switch,
  o  the most recent CCR value received from the source in a forward
      RM-cell

      The switch recomputes new values for a switch's Explicit Rate
on a periodic basis--That is, the computation of ER is driven by a
locally maintained timer, T(comp), rather than by receipt of forward
RM-cells from the source.  New "ER" values will only be recomputed
for active sources: namely, those from which the switch has received
at least one forward RM-cell within a previous T(comp) time
interval.  Hence, the "ER" value...