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Asynchronous Priority Scheme for Full-duplex Ring With Fairness

IP.com Disclosure Number: IPCOM000100757D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 6 page(s) / 172K

Publishing Venue

IBM

Related People

Cidon, I: AUTHOR [+2]

Abstract

This article describes an asynchronous priority scheme for the full- duplex buffer insertion ring, which uses the global fairness mechanism. The solution preserves the fairness among users which operates under the same priority level while restricting the access of lower priority traffic to the network when congestion of higher priority traffic occurs.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 34% of the total text.

Asynchronous Priority Scheme for Full-duplex Ring With Fairness

       This article describes an asynchronous priority scheme
for the full- duplex buffer insertion ring, which uses the global
fairness mechanism. The solution preserves the fairness among users
which operates under the same priority level while restricting the
access of lower priority traffic to the network when congestion of
higher priority traffic occurs.

      The hardware control messages are used for exchange of state
information between neighboring nodes. These messages can be used for
source fairness, back pressure and overflow prevention, and have the
following characteristics:
      Very short - few characters (possibly one).
      Preemptive priority - can be sent in the middle of a
      data packet.
      Non-distructive - does not damage the data packets
      which they preempt.
      Delay - virtually only the link propagation delay (no
      queueing delay).
      Independent hardware - used for the ring control
      mechanism.

      The access on each direction of the ring is regulated by a
control message, SAT, which circulates in the opposite direction to
the data traffic it is regulating.  The access is completely fair
(all nodes have equal opportunity), while maintaining most of the
potential spatial reuse in the full-duplex buffer insertion ring.

      The figure describes the basic SAT mechanism for one direction
of the ring.  In this case the data is transferred down-stream, and
the SAT message is transferred up-stream.

      In principle, the node will forward the SAT message up-stream
with no delay, unless it is "starved."  By "starved," we mean that
the node could not send the permitted number of messages since the
last time it has forwarded the SAT message.

      Priority Schemes for the Asynchronous Traffic The basic
fairness protocol allows the regulation and prevents starvation for
the nodal asynchronous traffic. However, the basic scheme treats all
traffic at the same priority level.  The implementation of priority
levels among various types of asynchronous traffic is the issue of
this section.  The solution preserves the fairness among users which
operates under the same priority level while restricting the access
of lower priority traffic to the network when congestion of higher
priority traffic occurs.

      Informal Description The basic idea is to assign a priority
level to the SAT message such that only packets with priority equal
or higher than this level are allowed to be transmitted.  Every node
can increase the priority level of the SAT if it has packets of
higher priority than the current priority level of the SAT.  The
basic problems that are to be solved are how and when to decrease the
value of the SAT message to some lower priority level and to what
level.

      The algorithm is designed such that the node that last
increased the priority...