Bootstrapping and Mesh topologies
Applications of 6LoWPAN most often involve completely autonomous devices and networks, which must autoconfigure themselves without human intervention. Bootstrapping first needs to be performed by the link layer, in order to enable basic communication between nodes within radio range. Basic link layer configuration usually involves the channel setting, default security key and address settings. Once the link layer is functioning and single-hop communications between devices is possible, 6LoWPAN Neighbor Discovery [ID-6lowpan-nd] is used to bootstrap the whole LoWPAN.
Neighbor Discovery is a key feature of IPv6, which handles most basic bootstrapping and maintenance issues between nodes on IPv6 links. Basic IPv6 Neighbor Discovery is specified in [RFC4861], but is not suitable for use with 6LoWPAN. The 6LoWPAN working group has defined 6LoWPAN Neighbor Discovery (6LoWPAN-ND) optimized for low-power wireless networks and 6LoWPAN in particular [ID-6lowpan-nd].
The 6LoWPAN-ND specification describes network autoconfiguration and the operation of hosts, routers and edge routers in LoWPANs. A registry of the nodes in each LoWPAN is kept in the corresponding edge router, which simplifies IPv6 operation across the network and reduces the amount of multicast flooding. Additionally 6LoWPAN-ND enables LoWPANs covering many edge routers connected by a common backbone link (e.g. Ethernet), and the unique generation of short link-layer addresses. Chapter 3 looks at bootstrapping issues and Neighbor Discovery in detail. See Appendix A for a reference on basic Neighbor Discovery.
1.3.6 Mesh topologies
Mesh topologies are common in applications of 6LoWPAN such as automatic meter reading and environmental monitoring. A mesh topology extends the coverage of the network, and reduces the cost of needed infrastructure. In order to achieve a mesh topology, multihop forwarding is required from one node to another. In 6LoWPAN this can be done in three different ways: link-layer mesh, LoWPAN mesh or IP routing. Link-layer mesh and LoWPAN mesh are referred to as Mesh-Under as the mesh forwarding is transparent to the Internet Protocol. IP routing is referred to as Route-Over.
Link-layer mesh is possible with some wireless technologies that include multihop forwarding features such as the recently completed IEEE 802.15.5 standard [IEEE802.15.5]. The original 6LoWPAN specification [RFC4944] includes an option for carrying mesh source and destination addresses, which can be used by a forwarding algorithm. No standard algorithms for use with this mesh header have been defined, and therefore the realization of LoWPAN mesh has been implementation specific. Currently, the most common technique instead employs IP routing.
Routing with 6LoWPAN works just as with standard IP stacks, an algorithm updates a routing table which IP uses to make next-hop decisions. The Internet protocol is agnostic to the routing algorithm, and simply forwards packets. IP routing algorithms for mesh networking are developed in the IETF MANET working group [MANET] for generic ad hoc networks, and in the IETF ROLL working group [ROLL] specific to wireless embedded applications such as industrial and building automation. IP routing issues and algorithms are discussed in detail in Section 4.2 including information on ROLL.