'''Multiple Access with Collision Avoidance for Wireless''' ('''MACAW''')<ref name="MACAW">{{cite journal|author=Vaduvur Bharghavan et al. |title=MACAW: A Medium Access Protocol for Wireless LAN's|url=http://pdos.csail.mit.edu/decouto/papers/bharghavan94.pdf|version=In the Proc. ACM SIGCOMM Conference (SIGCOMM '94), August 1994, pages 212-225|date=1994-08-01|accessdate=2007-01-18}}</ref> is a slotted [[Medium Access Control]] (MAC) protocol widely used in [[Adad hoc network|ad hoc networks]]s.<ref name="SMAC_1">{{cite journal |author=Wei Ye et al. |title=An Energy-Efficient MAC Protocol for Wireless Sensor Networks |url=http://www.isi.edu/~weiye/pub/smac_infocom.pdf|version=INFOCOM 2002|date=2002-06-01|accessdate=2006-11-26 |archiveurl = http://web.archive.org/web/20061104045110/http://www.isi.edu/~weiye/pub/smac_infocom.pdf |archivedate = 2006-11-04}}</ref> Furthermore, it is foundation of many other [[Medium Access Control|MAC]] protocols used in [[Wireless Sensor Networks]] (WSN).<ref name="SMAC_1"/> The [[IEEE 802.11 RTS/CTS]] mechanism is adopted from this protocol.<ref name="SMAC_2">{{cite journal |author=Wei Ye et al. |title=Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks |url=http://www.isi.edu/~weiye/pub/smac_ton.pdf|version=IEEE/ACM Transactions on Networking, Vol. 12, No. 3, pp. 493-506, June 2004|date=2004-06-01|accessdate=2006-12-27 |archiveurl = http://web.archive.org/web/20061209195620/http://www.isi.edu/~weiye/pub/smac_ton.pdf |archivedate = 2006-12-09}}</ref><ref name=holger>{{cite book | last = Karl| first = Holger | authorlink = Holger Karl | year = 2005| title =Protocols and Architectures for Wireless Sensor Networks | publisher = Wiley | isbn = 0-470-09510-5 | page = 117}}</ref> It uses ''RTS-CTS-DS-DATA-ACK'' frame sequence for transferring data, sometimes preceded by an ''RTS-RRTS'' frame sequence, in view to provide solution to the [[hidden terminal problem]].<ref name="MACAW"/> Although protocols based on MACAW, such as [[S-MAC]], use [[carrier sense]] in addition to the RTS/CTS mechanism, MACAW does not make use of carrier sense.<ref name="MACAW"/>
== Principles of operation ==
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Assume that node A has data to transfer to node B.
Node A initiates the process by sending a ''Request to Send'' frame (RTS) to node B. The destination node (node B) replies with a ''Clear To Send'' frame (CTS). After receiving CTS, node A sends data. After successful reception, node B replies with an acknowledgement frame (ACK). If node A has to send more than one data fragment, it has to wait a random time after each successful data transfer and compete with adjacent nodes for the medium using the RTS/CTS mechanism.<ref name="MACAW"/>
Any node overhearing an RTS frame (for example node F or node E in the illustration) refrains from sending anything until a CTS is received, or after waiting a certain time. If the captured RTS is not followed by a CTS, the maximum waiting time is the RTS propagation time and the destination node turnaround time.<ref name="MACAW"/>
