Editing IEEE 802.15.4

{{Short description|IEEE standard for low-rate wireless personal area networks}}
{{broader|Personal area network}}
{{multiple issues|
{{primary sources|date=November 2018}}
{{more citations needed|date=February 2022}}
}}
'''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 [[physical layer]] and [[media access control]] for LR-WPANs, and is maintained by the [[IEEE 802.15]] working group, which defined the standard in 2003.<ref>IEEE 802.15 WPAN™ Task Group 4, http://www.ieee802.org/15/pub/TG4.html</ref>  It is the basis for the [[Zigbee]],<ref name="Zigbee">{{cite web |url=http://sensor-networks.org/index.php?page=0823123150 |title=Security in 802.15.4 and ZigBee networks |first=David |last=Gascón |date=February 5, 2009 |access-date=9 December 2010|archive-url=https://web.archive.org/web/20120319184855/http://sensor-networks.org/index.php?page=0823123150|archive-date=19 March 2012|url-status=dead}}</ref> [[ISA100.11a]],<ref name="ISA100">{{cite web | url = http://www.isa.org//MSTemplate.cfm?MicrositeID=1134&CommitteeID=6891 |title=ISA100 Committee Home Page | access-date=20 July 2011 }}</ref> [[WirelessHART]], [[MiWi]], [[6LoWPAN]], [[Thread (network protocol)|Thread]], [[Subnetwork Access Protocol|SNAP]], and [[Clear Connect Type X]]<ref>{{Cite web |date=January 2020 |title=Lutron Clear Connect RF Technology |url=https://assets.lutron.com/a/documents/clear_connect_technology_whitepaper.pdf |access-date=2025-03-18 |website=Lutron}}</ref> specifications, each of which further extends the standard by developing the upper [[protocol stack|layers]], which are not defined in IEEE 802.15.4.  In particular, [[6LoWPAN]] defines a binding for the [[IPv6]] version of the [[Internet Protocol]] (IP) over WPANs, and is itself used by upper layers such as [[Thread (network protocol)|Thread]].

== 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 [[Line-of-sight propagation|line of sight]] at a [[transfer rate]] of 250&nbsp;kbit/s. Bandwidth tradeoffs are possible to favor more radically [[Embedded system|embedded devices]] with even lower power requirements for increased battery operating time, through the definition of not one, but several physical layers. Lower transfer rates of 20 and 40&nbsp;kbit/s were initially defined, with the 100&nbsp;kbit/s rate being added in the current revision.

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 computing|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 and quality and energy detection.
# Support for time- and data-rate–sensitive applications through the ability to operate with either CSMA/CA or [[Time-division multiple access|TDMA]] access modes. The TDMA mode of operation is supported via the GTS feature of the standard.<ref>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/</ref>
# IEEE 802.15.4-conformant devices may use one of three possible [[Frequency allocation|frequency band]]s for operation (868/915/2450&nbsp;MHz).

== Protocol architecture ==
[[Image:IEEE 802.15.4 protocol stack.svg|thumb|upright=1.2 |IEEE 802.15.4 protocol stack]] 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 frequency|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&nbsp;MHz: Europe, allows one communication channel (2003, 2006, 2011<ref>[https://web.archive.org/web/20190208000626/https://standards.ieee.org/standard/802_15_4-2011.html IEEE Std 802.15.4-2011 8.1.2.2]</ref>) <!-- Note that the standard does specify three different PHYs for the only available channel in the 868 MHz band. There is still only one channel in the sense that the three PHYs will interfere with each other; channel hopping for example will be impossible.  -->
* 902–928&nbsp;MHz: North America, originally allowed up to ten channels (2003), but since has been extended to thirty (2006)
* 2400–2483.5&nbsp;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&nbsp;MHz bands with transfer rates of 20 and 40&nbsp;kbit/s, and one in the 2450&nbsp;MHz band with a rate of 250&nbsp;kbit/s.

'''The 2006 revision''' improves the maximum data rates of the 868/915&nbsp;MHz bands, bringing them up to support 100 and 250&nbsp;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&nbsp;MHz bands, using either binary or, optionally, offset [[phase-shift keying#Offset QPSK (OQPSK)|quadrature phase-shift keying]] (QPSK); in the 2450&nbsp;MHz band, using QPSK.

An optional alternative 868/915&nbsp;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&nbsp;MHz PHYs is possible.

Beyond these three bands, the IEEE 802.15.4c study group considered the newly opened 314–316&nbsp;MHz, 430–434&nbsp;MHz, and 779–787&nbsp;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&nbsp;MHz band in Japan. The first standard amendments by these groups were released in April 2009.

'''In August 2007''', [[IEEE 802.15.4a]] was released expanding the four PHYs available in the earlier 2006 version to six, including one PHY using direct sequence [[ultra-wideband]] (UWB) and another using [[Chirp Spread Spectrum|chirp spread spectrum]] (CSS). The UWB PHY is allocated frequencies in three ranges: below 1&nbsp;GHz, between 3 and 5&nbsp;GHz, and between 6 and 10&nbsp;GHz. The CSS PHY is allocated spectrum in the 2450&nbsp;MHz ISM band.<ref>IEEE Computer Society, (August 31, 2007). IEEE Standard 802.15.4a-2007</ref>

'''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&nbsp;MHz band using [[phase-shift keying#Offset QPSK (OQPSK)|O-QPSK]] or MPSK,<ref>IEEE Computer Society, (April 17, 2009). IEEE Standard 802.15.4c-2009</ref> another for 950&nbsp;MHz using [[Gaussian frequency-shift keying|GFSK]] or [[phase-shift keying#Binary phase-shift keying (BPSK)|BPSK]].<ref>IEEE Computer Society, (April 17, 2009). IEEE Standard 802.15.4d-2009</ref>

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 [[Beacon frame|beaconing]]. It also controls frame validation, guarantees [[Time-division multiplexing|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 frame]]s.  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 (network protocol)|Thread]], build on this standard. [[RIOT (operating system)|RIOT]], [[OpenWSN]], [[TinyOS]], Unison RTOS, DSPnano RTOS, nanoQplus, [[Contiki]] and [[Zephyr (operating system)|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 ===

[[Image:IEEE 802.15.4 Star P2P en.svg|thumb|IEEE 802.15.4 star and peer-to-peer]]
[[Image:IEEE 802.15.4 cluster tree.png|thumb|upright=1.3 |IEEE 802.15.4 cluster tree]]

Networks can be built as either [[peer-to-peer]] or [[Star network|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 network]]s capable of performing self-management and organization. Since the standard does not define a network layer, [[routing]] is not directly supported, but such an additional layer can add support for [[Multi-hop routing|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.

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 ==
[[Data frame|Frames]] are the basic unit of data transport, of which there are four fundamental types (data, acknowledgment, beacon and MAC command frames), which provide a reasonable tradeoff between simplicity and robustness. Additionally, a superframe structure, defined by the coordinator, may be used, in which case two beacons act as its limits and provide synchronization to other devices as well as configuration information. A superframe consists of sixteen equal-length slots, which can be further divided into an active part and an inactive part, during which the coordinator may enter power saving mode, not needing to control its network.

Within superframes [[Contention (telecommunications)|contention]] occurs between their limits, and is resolved by [[CSMA/CA]]. Every transmission must end before the arrival of the second beacon. As mentioned before, applications with well-defined bandwidth needs can use up to seven domains of one or more [[contention (telecommunications)|contention]]less guaranteed time slots, trailing at the end of the superframe. The first part of the superframe must be sufficient to give service to the network structure and its devices. Superframes are typically utilized within the context of low-latency devices, whose associations must be kept even if inactive for long periods of time.

Data transfers to the coordinator require a beacon synchronization phase, if applicable, followed by [[CSMA/CA]] transmission (by means of slots if superframes are in use); [[Acknowledgement (data networks)|acknowledgment]] is optional. Data transfers from the coordinator usually follow device requests: if beacons are in use, these are used to signal requests; the coordinator acknowledges the request and then sends the data in packets which are acknowledged by the device. The same is done when superframes are not in use, only in this case there are no beacons to keep track of pending messages.

Point-to-point networks may either use unslotted [[CSMA/CA]] or synchronization mechanisms; in this case, communication between any two devices is possible, whereas in "structured" modes one of the devices must be the network coordinator.

In general, all implemented procedures follow a typical request-confirm/indication-response classification.

== Reliability and security ==
The physical medium is accessed through a [[CSMA/CA]] access method. Networks which are not using beaconing mechanisms utilize an unslotted variation which is based on the listening of the medium, leveraged by a [[Exponential backoff|random exponential backoff]] algorithm; acknowledgments do not adhere to this discipline. Common data transmission utilizes unallocated slots when beaconing is in use; again, confirmations do not follow the same process.

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 (telecommunication)|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 key|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 list]]s. 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<ref name="Zigbee" /> merely as a means to decide on the acceptance of frames according to their (presumed) source.

== See also ==
* [[Bluetooth]]
* [[DASH7]]
* [[EnOcean]]
* [[INSTEON]]
* [[LoRa | LoRaWAN]]
* [[LPWAN]]
* [[NeuRFon]]
* [[Sigfox]]
* [[UWB ranging]]

==References==
{{Reflist|30em}}

==External links==
* [http://www.ieee802.org/15/pub/TG4.html 802.15.4 Task Group]
* [https://web.archive.org/web/20021222195607/http://standards.ieee.org/getieee802/802.15.html Get IEEE 802.15]
* [https://web.archive.org/web/20220216073909/https://standards.ieee.org/ieee/802.15.4z/10230/ IEEE standard 802.15.4z]
* [https://web.archive.org/web/20170618223341/http://standards.ieee.org/findstds/standard/802.15.4v-2017.html IEEE standard 802.15.4v-2017]
* [https://web.archive.org/web/20171109080916/https://standards.ieee.org/findstds/standard/802.15.4u-2016.html IEEE standard 802.15.4u-2016]
* [https://web.archive.org/web/20170929183340/https://standards.ieee.org/findstds/standard/802.15.4t-2017.html IEEE standard 802.15.4t-2017]
* [https://web.archive.org/web/20200316075520/https://standards.ieee.org/standard/802_15_4q-2016.html IEEE standard 802.15.4q-2016]
* [https://web.archive.org/web/20200307130248/https://standards.ieee.org/standard/802_15_4p-2014.html IEEE standard 802.15.4p-2014]
* [https://web.archive.org/web/20200311045712/https://standards.ieee.org/standard/802_15_4n-2016.html IEEE standard 802.15.4n-2016]
* [https://standards.ieee.org/ieee/802.15.4m/5327/ IEEE standard 802.15.4m-2014]
* [https://standards.ieee.org/ieee/802.15.4k/5019/ IEEE standard 802.15.4k-2013]
* [https://standards.ieee.org/ieee/802.15.4j/5018/ IEEE standard 802.15.4j-2013]
* [https://standards.ieee.org/ieee/802.15.4g/5053/ IEEE standard 802.15.4g-2012]
* [https://standards.ieee.org/ieee/802.15.4f/5052/ IEEE standard 802.15.4f-2012]
* [https://standards.ieee.org/ieee/802.15.4e/5051/ IEEE standard 802.15.4e-2012]
* [https://standards.ieee.org/ieee/802.15.4d/4151/ IEEE standard 802.15.4d-2009]
* [https://standards.ieee.org/ieee/802.15.4c/4239/ IEEE standard 802.15.4c-2009]
* [https://standards.ieee.org/ieee/802.15.4a/3571/ IEEE standard 802.15.4a-2007]
* [https://standards.ieee.org/ieee/802.15.4/7029/ IEEE standard 802.15.4-2020]
* [https://standards.ieee.org/ieee/802.15.4-2015_Cor_1/7059/ IEEE standard 802.15.4-2015]
* [https://standards.ieee.org/ieee/802.15.4/5050/ IEEE standard 802.15.4-2011]
* [https://web.archive.org/web/20200801200327/https://standards.ieee.org/content/ieee-standards/en/standard/802_15_4-2006.html IEEE standard 802.15.4-2006]
* [https://web.archive.org/web/20190123010831/https://standards.ieee.org/content/ieee-standards/en/standard/802_15_4-2003.html IEEE standard 802.15.4-2003]

{{IEEE standards}}
{{Authority control}}

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[[Category:IEEE 802]]
[[Category:Wireless networking standards]]