Confirmation messages may be optional under certain circumstances in which case

Confirmation messages may be optional under certain

This preview shows page 28 - 30 out of 39 pages.

Confirmation messages may be optional under certain circumstances, in which case a success assumption is made. Whatever the case, if a device is unable to process a frame at a given time, it simply does not confirm its reception: timeout-based retransmission can be performed a number of times, following after that a decision of whether to abort or keep trying. Because the predicted environment of these devices demands maximization of battery life, the protocols tend to favor the methods which lead to it, implementing periodic checks for pending messages, the frequency of which depends on application needs. Regarding secure communications, the MAC sublayer offers facilities which can be harnessed by upper layers to achieve the desired level of security. Higher-layer processes may specify keys to perform symmetric cryptography to protect the payload and restrict it to a group of devices or just a point-to-point link; these groups of devices can be specified in access control lists. Furthermore, MAC computes freshness checks between successive receptions to ensure that presumably old frames, or data which is no longer considered valid, does not transcend to higher layers. In addition to this secure mode, there is another, insecure MAC mode, which allows access control lists [1] merely as a means to decide on the acceptance of frames according to their (presumed) source. References [2] IEEE Computer Society, (August 31, 2007). IEEE Standard 802.15.4a-2007 [3] http:/ / en. wikipedia. org/ wiki/ Phase-shift_keying#Offset_QPSK_. 28OQPSK. 29 [4] IEEE Computer Society, (April 17, 2009). IEEE Standard 802.15.4c-2009 [5] http:/ / en. wikipedia. org/ wiki/ Gaussian_frequency-shift_keying [6] http:/ / en. wikipedia. org/ wiki/ Phase-shift_keying#Binary_phase-shift_keying_. 28BPSK. 29 [7] IEEE Computer Society, (April 17, 2009). IEEE Standard 802.15.4d-2009 External links 802.15.4 Task Group (http:/ / www. ieee802. org/ 15/ pub/ TG4. html) Get IEEE 802.15 (http:/ / standards. ieee. org/ getieee802/ 802. 15. html) IEEE standard 802.15.4d-2009 (http:/ / standards. ieee. org/ getieee802/ download/ 802. 15. 4d-2009. pdf) IEEE standard 802.15.4c-2009 (http:/ / standards. ieee. org/ getieee802/ download/ 802. 15. 4c-2009. pdf) IEEE standard 802.15.4a-2007 (http:/ / standards. ieee. org/ getieee802/ download/ 802. 15. 4a-2007. pdf) IEEE standard 802.15.4-2011 (http:/ / standards. ieee. org/ getieee802/ download/ 802. 15. 4-2011. pdf) IEEE standard 802.15.4-2006 (http:/ / standards. ieee. org/ getieee802/ download/ 802. 15. 4-2006. pdf) IEEE standard 802.15.4-2003 (http:/ / standards. ieee. org/ getieee802/ download/ 802. 15. 4-2003. pdf) 802.15.4 Resources (http:/ / www. daintree. net/ resources/ index. php) including whitepapers and glossary] 802.15.4 vs ZigBee (http:/ / sensor-networks. org/ index. php?page=0823123150) Security in 802.15.4 and ZigBee networks (http:/ / sensor-networks. org/ index. php?page=0903503549)
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Wireless ad hoc network 27 Wireless ad hoc network A wireless ad hoc network is a decentralized type of wireless network. [1] The network is ad hoc because it does not rely on a pre existing infrastructure, such as routers in wired networks or access points in managed (infrastructure) wireless networks. Instead, each node participates in routing by forwarding data for other nodes, so the determination of which nodes forward data is made dynamically on the basis of network connectivity. In addition to the classic
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  • Fall '18
  • Mr. Bhullar
  • Test, Wireless sensor network, TinyOS, zigbee

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