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Understanding 6LoWPAN: The wireless embedded Internet (Part 3)

Posted: 26 Sep 2011     Print Version  Bookmark and Share

Keywords:Wireless Embedded Internet  stub network  IPv6 

The Wireless Embedded Internet is built by connecting islands of wireless embedded devices, each island being a stub network on the Internet. A stub network is a network which IP packets are sent from or destined to, but which doesn't act as a transit to other networks.

The 6LoWPAN architecture is made up of low-power wireless area networks (LoWPANs), which are IPv6 stub networks. The overall 6LoWPAN architecture is presented in the. Three different kinds of LoWPANs have been defined: Simple LoWPANs, Extended LoWPANs, and Ad hoc LoWPANs.

A LoWPAN is the collection of 6LoWPAN Nodes which share a common IPv6 address prefix (the first 64 bits of an IPv6 address), meaning that regardless of where a node is in a LoWPAN its IPv6 address remains the same. An Ad hoc LoWPAN is not connected to the Internet, but instead operates without an infrastructure. A Simple LoWPAN is connected through one LoWPAN Edge Router to another IP network. A backhaul link (point-to-point, e.g. GPRS) is shown in the figure, but this could also be a backbone link (shared). An Extended LoWPAN encompasses the LoWPANs of multiple edge routers along with a backbone link (e.g. Ethernet) interconnecting them.

6LoWPAN architecture

Figure: An illustration of the 6LoWPAN architecture.

LoWPANs are connected to other IP networks through edge routers, as seen in the figure. The edge router plays an important role as it routes traffic in and out of the LoWPAN, while handling 6LoWPAN compression and NeighbourDiscovery for the LoWPAN. If the LoWPAN is to be connected to an IPv4 network, the edge router will also handle IPv4 interconnectivity (discussed further in Section 4.3). Edge routers typically have management features tied into overall IT management solutions. Multiple edge routers can be supported in the same LoWPAN if they share a common backbone link.

A LoWPAN consists of nodes, which may play the role of host or router, along with one or more edge routers. The network interfaces of the nodes in a LoWPAN share the same IPv6 prefix which is distributed by the edge router and routers throughout the LoWPAN. In order to facilitate efficient network operation, nodes register with an edge router. These operations are part of Neighbour Discovery (ND), which is an important basic mechanism of IPv6.

Neighbour Discovery defines how hosts and routers interact with each other on the same link. LoWPAN Nodes may participate in more than one LoWPAN at the same time (called multi-homing), and fault tolerance can be achieved between edge routers. LoWPAN Nodes are free to move throughout the LoWPAN, between edge routers, and even between LoWPANs. Topology change may also be caused by wireless channel conditions, without physical movement. A multi-hop mesh topology within the LoWPAN is achieved either through link-layer forwarding (called Mesh-Under) or using IP routing (called Route-Over). Both techniques are supported by 6LoWPAN.

Communication between LoWPAN Nodes and IP nodes in other networks happens in an end-to-end manner, just as between any normal IP nodes. Each LoWPAN Node is identified by a unique IPv6 address, and is capable of sending and receiving IPv6 packets. Typically LoWPAN Nodes support ICMPv6 traffic such as "ping", and use the user datagram protocol (UDP) as a transport. In the figure, the Simple LoWPAN and Extended LoWPAN Nodes can communicate with either of the servers through their edge router. As the payload and processing capabilities of LoWPAN Nodes are extremely limited, application protocols are usually designed using a simple binary format in a UDP payload. Application protocols suitable for 6LoWPAN are discussed in the succeeding part of this series.

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