IEEE 802.15.4 in the IOT Reference Architecture
1. IOT Reference Architecture structure
IOT Reference Architecture consists of the following blocks.
2. What is 802.15.4?
802.15.4 covers all the low power low data rate wireless communication standards in PHY/MAC Datalink layer in the ISO/OSI model.
3. What are the functionalities of Physical layer?
- Data encoding: Modifies the digital signal pattern to suit the characteristics of the physical medium along with bit and frame synchronization.
- Physical medium hardware requirements (such as if an external transceiver is required and how many pins the connector has and what each of them is used for)
- Transmission technique: If the encoded bits will be transmitted by digital or analog signaling.
- Physical medium transmission: Transmission voltage levels, optical or electrical transmission etc.
4. What are the functionalities of Data Link Layer?
- Link establishment and termination
- Sequential transmission of frames
- Frame acknowledgment
- Frame delimiting
- Frame error checking
- Media access management: Determines when the node can access the physical medium.
5. Main characteristics of 802.15.4
- Maximum data rate is 250 Kbps
- Maximum output power is 1mW
- 802.15.4 devices have range in the order of a few tens of meters.
- Used for low power, low data rate applications.
- Prescribed frequency bands — 915 MHz and 2.4 GHz.
6. Popular 802.15.4 implementations
- Zigbee
- WirelessHART
- ANSI/ISA100.11a
- 6LoWPAN
7. Packet Size and Structure
As shown in Fig 2, the maximum packet size in 802.15.4 is 127 bytes. But the available data for upper layer protocol is between 81 and 122 bytes since the MAC layer adds a header to each packet. Hence upper layer protocols usually fragment larger data portions to multiple 802.15.4 frames.
Citations
[1] Mohanty, Sanatan. (2010). Energy Efficient Routing Algorithms for Wireless Sensor Networks and Performance Evaluation of Quality of Service for IEEE 802.15.4 Networks.
