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IEEE 802.15.4

IEEE 802.15.4 is a low-cost, low-data-rate wireless access technology for devices that are operated or work on batteries.

 IEEE 802.15. Protocol Stacks include:

• ZigBee: ZigBee is a Personal Area Network task group with a low rate task group 4. It is a technology of home networking. ZigBee is a technological standard created for controlling and sensing the network. As we know that ZigBee is the Personal Area network of task group 4 so it is based on IEEE 802.15.4 and is created by Zigbee Alliance. 
• 6LoWPAN: The 6LoWPAN system is used for a variety of applications including wireless sensor networks. This form of wireless sensor network sends data as packets and uses IPv6 – providing the basis for the name – IPv6 over Low power Wireless Personal Area Networks.
• ZigBee IP: Zigbee is a standards-based wireless technology that was developed for low-cost and low-power wireless machine-to-machine (M2M) and internet of things (IoT) networks.
• ISA100.11a: It is a mesh network that provides secure wireless communication to process control.
• Wireless HART: It is also a wireless sensor network technology, that makes use of time-synchronized and self-organizing architecture.
• Thread: Thread is an IPv6-based networking protocol for low-power Internet of Things devices in IEEE 802.15. 4-2006 wireless mesh network. Thread is independent.

Protocol architecture

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)

Physical Layer: 

This standard enables a wide range of PHY options in ISM bands, ranging from 2.4 GHz to sub-GHz frequencies. IEEE 802.15.4 enables data transmission speeds of 20 kilobits per second, 40 kilobits per second, 100 kilobits per second, and 250 kilobits per second. The fundamental structure assumes a 10-meter range and a data rate of 250 kilobits per second. To further reduce power usage, even lower data rates are possible. IEEE 802.15.4 regulates the RF transceiver and channel selection, and even some energy and signal management features, at the physical layer. Based on the frequency range and data performance needed, there are now six PHYs specified. Four of them employ frequency hopping techniques known as Direct Sequence Spread Spectrum (DSSS). Both PHY data service and management service share a single packet structure so that they can maintain a common simple interface with MAC.

 MAC layer:

 The MAC layer provides links to the PHY channel by determining that devices in the same region will share the assigned frequencies. The scheduling and routing of data packets are also managed at this layer.  The 802.15.4 MAC layer is responsible for a number of functions like:

• Beaconing for devices that operate as controllers in a network.
• used to associate and dissociate PANs with the help of devices.
• The safety of the device.
• Consistent communication between two MAC devices that are in a peer-to-peer relationship.

Several established frame types are used by the MAC layer to accomplish these functions. In 802.15.4, there are four different types of MAC frames:

• frame of data
• Frame for a beacon
• Frame of acknowledgement
• Frame for MAC commands

Topology: 

Networks based on IEEE 802.15.4 can be developed in a star, peer-to-peer, or mesh topology. Mesh networks connect a large number of nodes. This enables nodes that would otherwise be out of range to interact with each other to use intermediate nodes to relay data.

Security: 

For data security, the IEEE 802.15.4 standard employs the Advanced Encryption Standard (AES) with a 128-bit key length as the basic encryption technique. Activating such security measures for 802.15.4 significantly alters the frame format and uses a few of the payloads. The very first phase in activating AES encryption is to use the Security Enabled field in the Frame Control part of the 802.15.4 header. For safety, this field is a single bit which is assigned to 1. When this bit is set, by taking certain bytes from its Payload field, a field known as the Auxiliary Security Header is formed following the Source Address field.