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Global Fairness Algorithm for a Full-Duplex Slotted Ring

IP.com Disclosure Number: IPCOM000100761D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 90K

Publishing Venue

IBM

Related People

Cidon, I: AUTHOR [+2]

Abstract

This article describes a mechanism for ensuring fair access in a full- duplex slotted ring. The access on each direction of the ring is regulated by a control bit, SAT, which is part of the header of the slot in the opposite direction. As a result, the access is completely fair, while maintaining the potential spatial reuse in the full-duplex ring.

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

Global Fairness Algorithm for a Full-Duplex Slotted Ring

       This article describes a mechanism for ensuring fair
access in a full- duplex slotted ring.  The access on each direction
of the ring is regulated by a control bit, SAT, which is part of the
header of the slot in the opposite direction.  As a result, the
access is completely fair, while maintaining the potential spatial
reuse in the full-duplex ring.

      Slotted ring is a distributed technique for accessing a ring
network and is suitable for the transmission of a fixed-size packet.
For this scheme the following is assumed:
1.   The node can transmit a packet only if it receives an empty
slot.
2.   The slot size and the packet size are the same.
3.   The packet is removed by the destination node, and then the slot
becomes empty.
4.   Packets are transmitted via the shortest path in the full-duplex
ring.

      The primary deficiency of a slotted ring is that a node can be
come unable to transmit packets, for an unbounded time, i.e., a node
can be "starved."  For example, on a full-duplex ring node i is
starved when its right neighbor i+1 is transmitting continuously to
the left and its left neighbor i-1 is transmitting continuously to
the right.

      Slotted ring is an access technique to a unidirectional ring
network.  The transmission time over the ring is divided into time
slots of fixed duration, Ts .  The number of time slots which exists
on the ring at any given time is constant, say, k.  If the number of
nodes on the ring is n, the delay of traversing a node is Wnode and
the propagation delay around the ring is Wring,  then the following
relation should hold:

                            (Image Omitted)

kTs< nWnode + Wring

      The value of Wnode is determined by decoding and
synchronization requirements.  On the receiving side of each link
there is an elastic buffer (EB), which is used for synchronizing
nodes with slightly different transmissi...