The MAC layer The medium access control MAC enables the transmission of MAC

The mac layer the medium access control mac enables

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external interference and persistent multi-path fading. The MAC layer The medium access control (MAC) enables the transmission of MAC frames through the use of the physical channel. Besides the data service, it offers a management interface and itself manages access to the physical channel and network beaconing. It also controls frame validation, guarantees time slots and handles node associations. Finally, it offers hook points for secure services. Note that the IEEE 802.15 standard does NOT use 802.1D or 802.1Q, i.e., it does not exchange standard Ethernet frames. The physical frame-format is specified in IEEE802.15.4-2011 in section 5.2. Higher layers Other higher-level layers and interoperability sublayers are not defined in the standard. There exist specifications, such as 6LoWPAN and ZigBee, which build on this standard to propose integral solutions. TinyOS, Unison RTOS, DSPnano RTOS and Contiki stacks also use a few items of IEEE 802.15.4 hardware. Network model Node types The standard defines two types of network node. The first one is the full-function device (FFD). It can serve as the coordinator of a personal area network just as it may function as a common node. It implements a general model of communication which allows it to talk to any other device: it may also relay messages, in which case it is dubbed a coordinator (PAN coordinator when it is in charge of the whole network). On the other hand there are reduced-function devices (RFD). These are meant to be extremely simple devices with very modest resource and communication requirements; due to this, they can only communicate with FFDs and can never act as coordinators. Topologies IEEE 802.15.4 star and peer-to-peer Networks can be built as either peer-to-peer or star networks. However, every network needs at least one FFD to work as the coordinator of the network. Networks are thus formed by groups of devices separated by suitable distances. Each device has a unique 64-bit identifier, and if some conditions are met short 16-bit identifiers can be used within a restricted environment. Namely, within each PAN domain, communications will probably use short identifiers. Peer-to-peer (or point-to-point) networks can form arbitrary patterns of connections, and their extension is only limited by the distance between each pair of nodes. They are meant to serve as the basis for ad hoc networks capable of performing self-management and organization. Since the standard does not define a network layer,
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IEEE 802.15.4 25 IEEE 802.15.4 cluster tree routing is not directly supported, but such an additional layer can add support for multihop communications. Further topological restrictions may be added; the standard mentions the cluster tree as a structure which exploits the fact that an RFD may only be associated with one FFD at a time to form a network where RFDs are exclusively leaves of a tree, and most of the nodes are FFDs. The structure can be extended as a generic mesh network whose nodes are cluster tree networks with a local coordinator for each cluster, in addition to the global coordinator.
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  • Fall '18
  • Mr. Bhullar
  • Test, Wireless sensor network, TinyOS, zigbee

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