6LoWPAN basics tutorial
- tutorial and essential information about the 6LoWPAN IP low power wireless PAN system aimed at wireless sensor networks and built upon IEEE 802.15.4 technology.
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 using IPv6 - providing the basis for the name - IPv6 over Low power Wireless Personal Area Networks.
6LoWPAN provides a means of carrying packet data in the form of IPv6 over IEEE 802.15.4 networks. Using the fact that IPv4 addresses are running short, and with the possible explosion of devices with allocated IP addresses, 6LoWPAN starts by using IPv6 as the basic IP format.
In this way, 6LoWPAN adopts a different approach to the other low power wireless sensor network solutions.
6LoWPAN and IETF
With the IETF, Internet Engineering Task Force, an organisation that defines and promotes standards used on the Internet. Accordingly using IP, or Internet Protocol, IP over wireless sensor networks falls into their area of influence.
The 6LoWPAN group within the IETF uses the IEEE 802.15.4 standard to provide the lower layer elements of this wireless network wireless sensor network. The 6LoWPAN group have then defined the encapsulation and compression mechanisms that enable the IPv6 data to be carried of the wireless network.
The development of the 6LoWPAN system was not as easy as might be thought as the basic natures of the two systems are very different. However it was believed that using packet data over a low power wireless sensor network would offer significant advantages in terms of data handling and management.
The specification number for 6LoWPAN is RFC 4944 with the problem statement document being referred to as RFC 4919.
6LoWPAN application areas
With many low power wireless sensor networks and other forms of ad hoc wireless networks, it is necessary that any new wireless system or technology has a defined area which it addresses. While there are many forms of wireless networks including wireless sensor networks, 6LoWPAN addresses an area that is currently not addressed by any other system, i.e. that of using IP, and in particular IPv6 to carry the data.
The overall system is aimed at providing wireless internet connectivity at low data rates and with a low duty cycle. Typical applications might include: general automation, entertainment applications in home, control and sensor networks for manufacturing applications or general site monitoring for industrial or other locations. Another application that may gain significant ground is for smart metering.
The 6LoWPAN technology utilises IEEE 802.15.4 to provide the lower layers for this low power wireless network system. While this seems a straightforward approach to the development of an packet data wireless network or wireless sensor network, there are incompatibilities between IPv6 format and the formats allowed by IEEE 802.15.4. This differences are overcome within 6LoWPAN and this allows the system to be used as a layer over the basic 802.15.4.
In order to send packet data, IPv6 over 6LowPAN, it is necessary to have a method of converting the packet data into a format that can be handled by the IEEE 802.15.4 lower layer system.
IPv6 requires the maximum transmission unit (MTU) to be at least 1280 bytes in length. This is considerably longer than the IEEE802.15.4's standard packet size of 127 octets which was set to keep transmissions short and thereby reduce power consumption.
To overcome the address resolution issue, IPv6 nodes are given 128 bit addresses in a hierarchical manner. The IEEE 802.15.4 devices may use either of IEEE 64 bit extended addresses or 16 bit addresses that are unique within a PAN after devices have associated. There is also a PAN-ID for a group of physically co-located IEEE802.15.4 devices.
Although 6LoWPAN is not as widely known as some other standards such as Zigbee, 6LoWPAN uses IPv6 and this alone has to set it aside from the others with a distinct advantage. With the world migrating towards packet data, a system such 6LoWPAN offers many advantages for low power wireless sensor networks and other forms of low power wireless networks.
By Ian Poole
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