Multiple Access with Collision Avoidance for Wireless: Difference between revisions

Revision as of 03:37, 21 March 2007

Revision as of 18:54, 5 October 2007

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=== RRTS <ref name="MACAW"/>===

Node D is unaware of the ongoing data transfer between node A and node B. Note D has data to send to node C, which is in the transmission range of node AD. D initiates the process by sending an RTS frame to node C. Node C has already deferred its transmission until the completion of the current data transfer between node A and node B (to avoid [[co-channel interference]] at node B). Hence, even though it receives RTS from node D, it does not reply back with CTS. Node D assumes that its RTS was not successful because of collision and hence ''backoff'' (using an [[exponential backoff]] algorithm).

If A has multiple data fragments to send, the only instant when node D successfully can initiate a data transfer is during small gaps in between that node A has completed data transfer and completion of node B next CTS (for node A next data transfer request). However, due to the node D backoff time period the probability to capture the medium during this small time interval is not high. To increase the per-node fairness, MACAW introduces a new control message called "Request for Request to Send" (RRTS).