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CRMA/Plus - Unallocated Slot Access With Reservation Look-Ahead and Buffer Insertion

IP.com Disclosure Number: IPCOM000122225D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 79K

Publishing Venue

IBM

Related People

Lemppenau, WW: AUTHOR [+2]

Abstract

A frame transmission via immediate access of unallocated slots in the CRMA (Cycle-Reservation Multiple-Access) MAC protocol [1,2] must be aborted upon arrival of a busy unallocated slot or a cycle comprising reserved slots. Frame abortions are avoidable by a look-ahead mechanism which guarantees that the frame length fits into the expected contiguous group of free unallocated slots and by a buffer insertion mechanism which resolves unexpected over- lapping unallocated-slot access activities of two or more independent nodes.

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CRMA/Plus - Unallocated Slot Access With Reservation Look-Ahead and
Buffer Insertion

      A frame transmission via immediate access of unallocated
slots in the CRMA (Cycle-Reservation Multiple-Access) MAC protocol
[1,2] must be aborted upon arrival of a busy unallocated slot or a
cycle comprising reserved slots. Frame abortions are avoidable by a
look-ahead mechanism which guarantees that the frame length fits into
the expected contiguous group of free unallocated slots and by a
buffer insertion mechanism which resolves unexpected over- lapping
unallocated-slot access activities of two or more independent nodes.

      We focus on the folded bus topology where slot reservations are
done via a reservation command (RES-command) on the same bus as data
transmissions (bus A); see Fig. 1.  Nodes receive data on the reverse
bus (bus B). Data and reservation operations in a dual bus system are
treated as two overlapped folded bus topologies. In CRMA, the headend
issues periodically RES-commands (cyclic numbered) collecting slot
reservations in their counterpart. Nodes add slot reservations for
only one frame transmission per command and remember the command
number.  Upon return, all reservations in a RES-command are either
completely accepted or rejected by the headend.  Each accepted
RES-command defines a numbered cycle of reserved slots issued by the
headend.  Since all reservations are made on bus A, the final
contents of the RES-commands can be monitored by any node when the
commands are relayed back to the headend on bus B.  Thus, every nod...