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Distributed Marking of Reserved Slots in a Reservation Based MAC Protocol for Ring Topologies

IP.com Disclosure Number: IPCOM000110062D
Original Publication Date: 1992-Oct-01
Included in the Prior Art Database: 2005-Mar-25
Document File: 4 page(s) / 205K

Publishing Venue

IBM

Related People

Lemppenau, WW: AUTHOR [+2]

Abstract

Consider a ring network with a slotted transmission structure where slots are accessed through two distinct mechanisms: immediate access of so-called gratis slots and access of previously reserved slots. A gratis/reserved flag is used to distinguish between both slot states. In either case, the busy/free flag needs to be free for the slot to be accessible. Reservation is done by a Reserve/Confirm command exchange where cyclically transmission requests are collected, requests are processed by a scheduling node, and confirmations are returned to the requesting nodes. Marking slots as reserved is done by the scheduler whereby a reservation is for only one transmission access. When a slot is freed by the destination, subsequent access to that slot is made via gratis access until the next marking takes place.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 39% of the total text.

Distributed Marking of Reserved Slots in a Reservation Based MAC Protocol for Ring Topologies

       Consider a ring network with a slotted transmission
structure where slots are accessed through two distinct mechanisms:
immediate access of so-called gratis slots and access of previously
reserved slots.  A gratis/reserved flag is used to distinguish
between both slot states.  In either case, the busy/free flag needs
to be free for the slot to be accessible. Reservation is done by a
Reserve/Confirm command exchange where cyclically transmission
requests are collected, requests are processed by a scheduling node,
and confirmations are returned to the requesting nodes.  Marking
slots as reserved is done by the scheduler whereby a reservation is
for only one transmission access.  When a slot is freed by the
destination, subsequent access to that slot is made via gratis access
until the next marking takes place.  Owing to this, a slot may be
re-used several times during one network roundtrip so that a
throughput far beyond the medium bit rate is achieved when the
traffic is dominantly local.  References (1,2) describe such a
protocol and demonstrate its property of combining high aggregate
throughput with fairness and tightly bounded delays.

      Here, a method is described to improve throughput and delay
performance one step further by distributing the marking function
dynamically among the active nodes on the network.  Two approaches
are discussed.  In the first one, slots are marked (as originally) by
setting the reserved flag in passing gratis slots (busy or free).
All nodes holding confirmations for the current reservation cycle are
allowed to use them.  In the second approach, marking of a slot is
done node-specific by means of an address-label.  In this case only
busy gratis slots are marked.  It is referred to the two approaches
as anonymous and labelled marking.  Both approaches use a method to
broadcast additional information as an integral part of the
reservation mechanism (3).  In the anonymous approach, this
information is the number of slots received by each node to identify
where slots become free.  In the labelled marking approach, the
address-labels of all active nodes are broadcast.

      Anonymous distributed marking consists basically in exploiting
the additional information where free slots potentially become
available so that the transportation of free reserved slots from one
part of the network to another is reduced.  The reservation procedure
is illustrated in Fig. 1.  The scheduler issues the Reserve command
(for cycle i) to collect the transmit counts and reservation requests
of all nodes.  The transmit count is the cumulated number of the
node's transmissions in gratis and reserved slots.  Each node
memorizes both counts when it inserts them into the Reserve command
because they continue to increase during the reservation procedure.
Upon return, the scheduler starts reservation processi...