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Wi-SUN Protocol Stack | Wi-SUN RF driver, PHY, MAC layer

This page describes Wi-SUN protocol stack layers. It explains functions of protocol layers of Wi-SUN stack viz. RF driver,PHY layer and MAC layer.

What is Wi-SUN ?

Wi-SUN is the short form of Wireless Smart Ubiquitous Network Field Area Network. Wi-SUN is a mesh topology based networking protocol unlike star based WiFi or LTE. Wi-SUN FAN (Field Area Network) supports greater number of end nodes to cover greater distances unlike Zigbee and Thread technologies.

Wi-SUN alliance is a consortium of global corporations or organizations from United States, Canada, Australia, China, Europe, Japan, Brazil, Korea, India etc. Members can be promoter, Contributor, observer or adopter of Wi-SUN technology. There are about 240 members across 40 countries. These world leaders manage Wi-SUN certification, interoperability and standardization process of Wi-SUN compliant devices.

The Wi-SUN supports various applications such as smart utility, smart city, Smart home, M2M and IoT (Internet of Things) markets across the world. The key use cases of Wi-SUN FAN are AMI metering, EV charging, Smart transport, SCADA, parking, distributed generation, environmental sensors, traffic management, smart lighting, direct load control and so on.

Wi-SUN uses <1GHz and 2.4 GHz frequency bands for its operation. Based on modulation techniques, it supports different symbol rates viz. 50, 100, 150, 200 and 300 Ksymbols/sec. It supports longer range which is about 4 Km point to point with 1W output from non-directional antenna. It offers very low latency of about 0.02 seconds.

Wi-SUN Protocol Stack

Wi-SUN Protocol Stack
Figure-1 : Wi-SUN Protocol Stack

The figure depicts Wi-SUN protocol stack layers. Physical layer specifications of Wi-SUN are defined in IEEE 802.15.4g and MAC layer specifications are defined in IEEE 802.15.4e standard. Wi-SUN FAN 1.0 devices are line powered and use FSK modulations where as FAN 1.1 devices are battery powered and use OFDM modulations. Let us understand functions of each of the protocol layers of Wi-SUN technology.

RF Layer : RF layer modulates physical layer data over RF carrier for transmission. It does the reverse during reception. It uses appropriate radio frequency for transmission and reception as per country wise Wi-SUN allocations. Wi-SUN uses 470-510MHz, 779-787MHz and 920.5-924.5MHz in China, 863-870MHz and 870-876MHz in Europe, or 920-928MHz in USA, Canada and Japan, 2.45 GHz worldwide.

PHY Layer : Physical layer provide services to MAC layer above and provide input to RF driver at the bottom. It modulates MAC layer information using FSK or OFDM modulation as per FAN profile. PHY layer supports different data rates. The PHY layer specifications are defined in IEEE 802.15.4g (i.e. IEEE 802.15.4-2015). Wi-SUN FSK supports multiple data rates up to 300 kbps. Robust error correction is supported in Wi-SUN FSK version. OFDM PHY offers higher spectrum efficiency. Wi-SUN OFDM supports data rates up to 2.4 Mbps.

Data Link Layer or MAC layer: The MAC layer is defined in IEEE 802.15.4e and IE extensions. It performs various functions such as frequency hopping, discovery/join, protocol dispatch (IEEE 802.15.9), Several frame exchange patterns etc. Wi-SUN FAN defines 7 frame formats for different services. It also defines its own IEs (Information Elements) to support certain operations. There are two types of IEs viz. Wi-SUN header IEs and Wi-SUN payload IEs. The MAC frames are advertisement frame, advertisement Solicit frame, configuration frame, Configuration Solicit frame, Acknowledgment frame, application Data frame from upper layer and EAPOL (Extensible Authentication Protocol over LAN) frame.

Network Layer : 6LoWPAN adaptation and header compression, DHCPv6 for IP address management, Routing using RPL, ICMPv6 and unicast/multicast forwarding.

Transport Layer : UDP protocol is used at this layer. TCP is optional protocol for implementation.

Application Layer : The different protocols are used as per application requirements such as MQTT, CoAP, HTTP, SCADA, DLMS and so on.

Security Layer : Wi-SUN supports 802.1X/EAP-TLS/PKI Authentication, 802.11i Key management, optional ETSI-TS-102-887-2 Node 2 Node Key management.

Wi-SUN Protocol Stack

➨Refer Wi-SUN technology >> which describes Wi-SUN FAN architecture and its elements viz. routers (i.e. nodes), border routers, WAN (Wide Area Network), NOC (Network Operation Center). It covers benefits or advantages of Wi-SUN technology.

References:
• Wi-SUN FAN Overview from tools.ietf.org
• wi-sun.org



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