IEEE 802.15.4
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IEEE 802.15.4 is a technical standard that defines the operation of a low-rate wireless personal area network (LR-WPAN). It specifies the
Overview
IEEE standard 802.15.4 is intended to offer the fundamental lower network layers of a type of wireless personal area network (WPAN), which focuses on low-cost, low-speed ubiquitous communication between devices. It can be contrasted with other approaches, such as Wi-Fi, which offers more bandwidth and requires more power. The emphasis is on very low-cost communication of nearby devices with little to no underlying infrastructure, intending to exploit this to lower power consumption even more.
The basic framework conceives a 10-meter communications range with
Even lower rates can be used, which results in lower power consumption. As already mentioned, the main goal of IEEE 802.15.4 regarding WPANs is the emphasis on achieving low manufacturing and operating costs through the use of relatively simple transceivers, while enabling application flexibility and adaptability.
Key 802.15.4 features include:
- Suitability for real-time applications with reservation of Guaranteed Time Slots (GTS)
- Collision avoidance through CSMA/CA
- Integrated support for secure communications
- Power management functions to adjust compromises of link speed speed and quality and energy detection
- Support for time- and data-rate–sensitive applications through the ability to operate with either CSMA/CA or TDMA access modes. The TDMA mode of operation is supported via the GTS feature of the standard.[4]
- IEEE 802.15.4-conformant devices may use one of three possible frequency bands for operation (868/915/2450 MHz).
Protocol architecture
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b5/IEEE_802.15.4_protocol_stack.svg/260px-IEEE_802.15.4_protocol_stack.svg.png)
Devices are designed to interact with each other over a conceptually simple wireless network. The definition of the network layers is based on the OSI model; although only the lower layers are defined in the standard, interaction with upper layers is intended, possibly using an IEEE 802.2 logical link control sublayer accessing the MAC through a convergence sublayer. Implementations may rely on external devices or be purely embedded, self-functioning devices.
The physical layer
The physical layer is the bottom layer in the OSI reference model used worldwide, and protocols layers transmit packets using it
The physical layer (PHY) provides the data transmission service. It also, provides an interface to the physical layer management entity, which offers access to every physical layer management function and maintains a database of information on related personal area networks. Thus, the PHY manages the physical radio transceiver, performs channel selection along with energy and signal management functions. It operates on one of three possible unlicensed frequency bands:
- 868.0–868.6 MHz: Europe, allows one communication channel (2003, 2006, 2011[5])
- 902–928 MHz: North America, originally allowed up to ten channels (2003), but since has been extended to thirty (2006)
- 2400–2483.5 MHz: worldwide use, up to sixteen channels (2003, 2006)
The original 2003 version of the standard specifies two physical layers based on direct-sequence spread spectrum (DSSS) techniques: one working in the 868/915 MHz bands with transfer rates of 20 and 40 kbit/s, and one in the 2450 MHz band with a rate of 250 kbit/s.
The 2006 revision improves the maximum data rates of the 868/915 MHz bands, bringing them up to support 100 and 250 kbit/s as well. Moreover, it goes on to define four physical layers depending on the modulation method used. Three of them preserve the DSSS approach: in the 868/915 MHz bands, using either binary or offset quadrature phase-shift keying (QPSK; the second of which is optional); in the 2450 MHz band, using QPSK.
An optional alternative 868/915 MHz layer is defined using a combination of binary keying and amplitude-shift keying (thus based on parallel, not sequential, spread spectrum; PSSS). Dynamic switching between supported 868/915 MHz PHYs is possible.
Beyond these three bands, the IEEE 802.15.4c study group considered the newly opened 314–316 MHz, 430–434 MHz, and 779–787 MHz bands in China, while the IEEE 802.15 Task Group 4d defined an amendment to 802.15.4-2006 to support the new 950–956 MHz band in Japan. The first standard amendments by these groups were released in April 2009.
In August 2007,
In April, 2009 IEEE 802.15.4c and IEEE 802.15.4d were released expanding the available PHYs with several additional PHYs: one for 780 MHz band using
IEEE 802.15.4e was chartered to define a MAC amendment to the existing standard 802.15.4-2006 which adopts a channel hopping strategy to improve support for the industrial market. Channel hopping increases robustness against external interference and persistent multi-path fading. On February 6, 2012, the IEEE Standards Association Board approved IEEE 802.15.4e which concluded all Task Group 4e efforts.
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. It is tailored to the fact that most IEEE 802.15.4 PHYs only support frames of up to 127 bytes (adaptation layer protocols such as the IETF's 6LoWPAN provide fragmentation schemes to support larger network layer packets).
Higher layers
No higher-level layers or interoperability sublayers are defined in the standard. Other specifications, such as Zigbee, SNAP, and 6LoWPAN/Thread, build on this standard. RIOT, OpenWSN, TinyOS, Unison RTOS, DSPnano RTOS, nanoQplus, Contiki and Zephyr operating systems also use some components of IEEE 802.15.4 hardware and software.
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
![](http://upload.wikimedia.org/wikipedia/en/thumb/6/66/IEEE_802.15.4_Star_P2P_en.svg/220px-IEEE_802.15.4_Star_P2P_en.svg.png)
![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/39/IEEE_802.15.4_cluster_tree.png/290px-IEEE_802.15.4_cluster_tree.png)
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
A more structured star pattern is also supported, where the coordinator of the network will necessarily be the central node. Such a network can originate when an FFD decides to create its own PAN and declare itself its coordinator, after choosing a unique PAN identifier. After that, other devices can join the network, which is fully independent from all other star networks.
Data transport architecture
Within superframes
Data transfers to the coordinator require a beacon synchronization phase, if applicable, followed by
Point-to-point networks may either use unslotted
In general, all implemented procedures follow a typical request-confirm/indication-response classification.
Reliability and security
The physical medium is accessed through a
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:
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
In addition to this secure mode, there is another, insecure MAC mode, which allows access control lists[2] merely as a means to decide on the acceptance of frames according to their (presumed) source.
See also
References
- ^ IEEE 802.15 WPAN™ Task Group 4, http://www.ieee802.org/15/pub/TG4.html
- ^ a b Gascón, David (February 5, 2009). "Security in 802.15.4 and ZigBee networks". Archived from the original on 19 March 2012. Retrieved 9 December 2010.
- ^ "ISA100 Committee Home Page". Retrieved 20 July 2011.
- ^ A. Mishra, C. Na and D. Rosenburgh, "On Scheduling Guaranteed Time Slots for Time Sensitive Transactions in IEEE 802.15.4 Networks," MILCOM 2007 - IEEE Military Communications Conference, Orlando, FL, USA, 2007, pp. 1-7. https://ieeexplore.ieee.org/abstract/document/4455149/
- ^ IEEE Std 802.15.4-2011 8.1.2.2
- ^ IEEE Computer Society, (August 31, 2007). IEEE Standard 802.15.4a-2007
- ^ IEEE Computer Society, (April 17, 2009). IEEE Standard 802.15.4c-2009
- ^ IEEE Computer Society, (April 17, 2009). IEEE Standard 802.15.4d-2009
External links
- 802.15.4 Task Group
- Get IEEE 802.15
- IEEE standard 802.15.4z
- IEEE standard 802.15.4v-2017
- IEEE standard 802.15.4u-2016
- IEEE standard 802.15.4t-2017
- IEEE standard 802.15.4q-2016
- IEEE standard 802.15.4p-2014
- IEEE standard 802.15.4n-2016
- IEEE standard 802.15.4m-2014
- IEEE standard 802.15.4k-2013
- IEEE standard 802.15.4j-2013
- IEEE standard 802.15.4g-2012
- IEEE standard 802.15.4f-2012
- IEEE standard 802.15.4e-2012
- IEEE standard 802.15.4d-2009
- IEEE standard 802.15.4c-2009
- IEEE standard 802.15.4a-2007
- IEEE standard 802.15.4-2020
- IEEE standard 802.15.4-2015
- IEEE standard 802.15.4-2011
- IEEE standard 802.15.4-2006
- IEEE standard 802.15.4-2003