6LoWPAN

from Wikipedia, the free encyclopedia

6LoWPAN is an acronym for " IPv6 over Low power Wireless Personal Area Network " ( English : IPv6 for WPAN with low energy consumption). 6LoWPAN is a communication protocol for radio data transmission and an IETF working group that is responsible for this standard.

The standard also includes header compression methods that make it more efficient to transmit IPv6 packets over IEEE 802.15.4 -based networks. The Internet protocol is the basis for the network structures of the Internet and for local networks. 6LoWPAN aims to be able to integrate wireless PANs into existing networks with the least possible effort.

The basic specification of the protocol, which was developed by the 6LoWPAN working group of the IETF, is recorded in RFC 4944 . Some problems of the 6LoWPAN are listed in RFC 4919 . Since the header compression from the original draft (HC1) only leads to good results in a few cases, a new method was introduced in RFC 6282 (IPHC) and the old one should no longer be used.

6LoWPAN adaptation layer

6LoWPAN stack in the OSI model

The main component of the 6LoWPAN protocol is the 6LoWPAN adaptation layer , which works on the switching level of the OSI model and takes on tasks such as header compression , packet fragmentation and defragmentation as well as routing in mesh networks.

Header compression

25 of the 127 bytes of the Maximum Transmission Unit (MTU) are used for the MAC layer. An optional additional layer that occupies a further 21 bytes for AES- CCM-128 encryption means that only 81 bytes remain for the layers above. The IPv6 header requires 40 bytes, the UDP header another 8 bytes, which means that only 33 bytes are available for user data. By compressing the IPv6 and UDP headers of 6LoWPAN, these two headers can ideally be compressed down to 7 bytes.

The compression of the addresses takes advantage of the fact that an address in IPv6 ideally consists of a 64-bit prefix for the subnet and a 64-bit suffix identical to the MAC address. If a packet is only transported over one hop, the suffix of the destination address is identical to the destination MAC address and the suffix of the sender address is identical to the MAC address of the sender and can therefore be omitted. If link-local addresses are used, the prefix can even be omitted. There is also the option of compressing addresses using contexts. However, the standard does not yet provide any information on how these contexts are exchanged.

Further compression options for the header are the flow label and the traffic class , which are often left at 0.

Packet fragmentation and defragmentation

IPv6 requires an MTU of at least 1280 bytes. However, IEEE 802.15.4 only provides a packet size of 127 bytes. The 6LoWPAN adaptation layer enables transparent fragmentation of the IP packets, so that a larger MTU is virtually available to them.

There are different approaches for dealing with fragmented packets when forwarding. The standard describes that a packet is completely received and reassembled on each node before it is forwarded to the next node. A faster approach, which also saves memory on the sensor nodes, is to forward the fragments directly. Since the IP header is already in the first fragment, all the information is already available to make a routing decision.

Routing

Mesh with internet connection (6LoWPAN gateway)

When routing in dynamic meshed networks (meshes) with moving network nodes, special problems arise:

  • Mobility of the knots
  • Accessibility of the individual nodes via IPv6 or IPv4
  • potentially large number of nodes
  • Node fluctuation (newly integrated nodes, loss of nodes, orphaned nodes)

Traditional routing protocols such as RIP , OSPF , IGRP or EIGRP are therefore only suitable to a limited extent for dynamic meshed networks.

Special routing protocols based on two basic approaches are being developed for dynamic meshes:

Mesh routing ( mesh-under ) and IP routing ( route-over )

Which routing is used ( mesh-under or route-over ) depends, among other things, on the requirements for which the mesh is designed; both variants have advantages and disadvantages.

One of the most popular algorithms for routing in meshed networks is the distance vector algorithm .

Mesh routing

In 6LoWPAN, with mesh routing, a mesh header is placed in front of the fragmentation and compression headers, which contains the start and destination ID of the nodes and the number of other jumps. This form of routing is called mesh-under .

With mesh-under, the start and destination ID of the nodes is not an IP address but, for example, the MAC address of the individual nodes. Information (MAC address) from the data link layer and thus the area of ​​network technology ( IEEE 802.15.4 ) is used to identify the nodes during routing .

Many of the mesh-under protocols in IEEE 802.15.4 use variants of the distance vector algorithm . In 6LoWPAN, a simplified form of the AODV protocol ( RFC 3561 ) is used in the 6LoWPAN Ad hoc Routing Protocol (LOAD) .

Further 6LoWPAN-specific mesh routing protocols are DYMO (Dynamic MANET On Demand) and HiLow (hierarchical routing protocol for 6LoWPAN).

IP routing

Routing based on IP ( Network Layer ) is called route-over (IP) . RPL is a 6LoWPAN-specific route-over protocol.

Hardware developments

One focus of the development of transceiver chips for IEEE 802.15.4 is currently (05/2014) determining the distance between two transceiver units by measuring the signal propagation time ( RF ranging ). As things stand, measurements with accuracies in the centimeter to millimeter range are possible.

This development is very likely to have an impact on future routing protocols.

A chip with this function is, for example, the AT86RF233 from Atmel, but research in this area is being promoted by all manufacturers.

Implementations

In the area of ​​open source:

  • 6LoWPAN implementation in Linux
  • 6LoWPAN implementation in Contiki
  • BLIP: 6LoWPAN implementation in TinyOS
  • 6LoWPAN implementation in RIOT

As proprietary implementations :

  • NanoStack and NanoRouter from Sensinode

See also

  • RPL - routing protocol designed for 6LoWPAN.

Web links

Individual evidence

  1. ↑ In 6LoWPAN: The Wireless Embedded Internet (Wiley, 2009), Shelby and Bormann redefine the 6LoWPAN acronym as "IPv6 over lowpower wireless area networks," arguing that "Personal" is no longer relevant to the technology.
  2. ↑ Ludovici, A .; Calveras, A .; Casademont, J. Forwarding Techniques for IP Fragmented Packets in a Real 6LoWPAN Network. Sensors 2011, 11, 992-1008. http://www.mdpi.com/1424-8220/11/1/992
  3. ↑ Andreas Weigel, Martin Ringwelski, Volker Turau and Andreas Timm-Giel. Route-Over Forwarding Techniques in a 6LoWPAN. In Proceedings of the 5th International Conference on Mobile Networks and Management (monami'13), September 2013. Cork, Ireland. http://link.springer.com/chapter/10.1007%2F978-3-319-04277-0_10
  4. ↑ a b Route-over vs mesh-under routing in 6LoWPAN
  5. ↑ [1] - RF ranging for location awareness
  6. ↑ a b [2] Distance measurement via RF
  7. ↑ [3] AT86RF233
  8. ↑ 6lowpan - Linux kernel
  9. ^ Contiki OS
  10. ↑ http://www.ece.iisc.ernet.in/6panview/wp-content/uploads/2010/11/website_techdocs/blip_implementation.pdf Genealogie Dead Link | url = http: //www.ece.iisc.ernet .in / 6panview / wp-content / uploads / 2010/11 / website_techdocs / blip_implementation.pdf | date = 2018-08 | archivebot = 2018-08-21 11:57:01 InternetArchiveBot}} (link not available)
  11. ^ RIOT-OS
  12. ↑ Sensinode's 6LoWPAN implementations ( Memento from August 13, 2014 in the Internet Archive )