Zach, I'm wondering if the term 'non-reflexive' in RFC4861 should have been 'non-symmetric'. Mathematically, an equivalence relationship is defined as being reflexive, symmetric and transitive. Symmetric is the property which is untrue on a unidirectional link not reflexive. Apologies if this is nonsense, I'm new to this list. Thanks Peter
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Zach Shelby Sent: 2009 May 12 10:38 To: 6lowpan Subject: [6lowpan] Terminology Hi, I am working on an updated terminology set for the nd draft. The terminology is now split with 6LoWPAN general terminology now in its own section. I would like comments on this updated set (below) where I have tried to find a solution based on the constructive discussions we had on the list. After looking through all the background RFCs in detail, it actually turns out this is not as hard as we thought. RFC4861 actually does cover the wireless case as it defines assymetric properties of wireless links including non-transitivity (see Section 2.2). In fact RFC4861 actually mentions that the protocol (ND) will presumably be extended in the future to deal with links that are assymetric (non-reflexive, non-transitive). That is what we are doing with ND for 6LoWPAN! Therefore I have now defined link as being non-transitive and complex NBMA, which can be somewhat overcome using link-layer mesh techniques or by with IP routing. This greatly simplifies the definition of a subnet (whew!), as we keep the RFC4291 where subnet <= link. As we are performing IP routing to overcome the non-transitive nature, the subnet does exhibit one aspect of multi-link subnet mentioned in RFC4903. IP routing has been defined as Alex recommended as it has specific properties to 6LoWPAN. In the architecture section of nd-03 we will include LoWPAN IP routing examples including topology and what is in the table. General 6LoWPAN Terminology: This section defines additional general terms related to the 6LoWPAN architecture used in this specification: IP Routing The forwarding of datagrams at the IP layer between arbitrary source-destination pairs, during which the hop limit is decremented. In the LoWPAN context, IP routing is performed by LoWPAN Routers on a single interface within the same link to overcome the non-transient nature of the link. Exact match search is performed on the dst address of the IP packet to find the next- hop to the destination. Referred to as routing in this document. Link The link is a communication facility or medium over which nodes can communicate at the link-layer, i.e., the layer directly below IP ([RFC4861]). 6LoWPAN assumes the use of low-power and lossy wireless links such as IEEE 802.15.4, which is a special type of link as described in [RFC4861] exhibiting severe assymetric reachability with both non-reflexive and non-transitive qualities. Furthermore complex Non-broadcast Multi-Access (NBMA) behaviour is exhibited as these links do not support native multicast, and broadcast reaches only a subset of nodes on the link. The use of link-layer mesh technology (see Mesh Under) emulates transitivity across the link but still has problems with non-reflexitivity. Multicast on a link-layer mesh is usually implemented as a broadcast flood. Link-local Standard IPv6 link-local scope as defined in [RFC4291] and [RFC4861] is supported by the 6LoWPAN link and subnet model. Link-local scope is achieved by setting the hop limit to 1, using link-local prefix or link-local multicast scope. If a link is non-transient then link-local scope includes only a subset of nodes on the link (the set of nodes within assymetric radio range of a node). Nodes in the link-local scope of a node are its neighbors, and this link-local scope may be different for each node on a link. LoWPAN Host A node that only sources or sinks IPv6 datagrams. Referred to as a host in this document. LoWPAN Node A node that composes a LoWPAN and is used to refer to both hosts and routers. Referred to as a node in this document. LoWPAN Router A node that forwards datagrams between arbitrary source- destination pairs using a single 6LoWPAN interface performing IP routing on that interface. Mesh Under A term referring to a configuration where the link-local scope is defined by the boundaries of the LoWPAN and includes all the 6LoWPAN interfaces within it. Forwarding and multihop routing functions are achieved at the link layer. In this configuration the link may still exhibit assymetric behaviour. Route Over A term referring to a configuration where the link is non- transient and the link-local scope reaches only a subset of the LoWPAN nodes. IP routing is performed by LoWPAN Routers to overcome to the non-transient nature of the link. This configuration may consist of both routers nad hosts. Subnet A subnet is the collection of interfaces having the same IPv6 subnet prefix on a link, as defined in [RFC4291]. A LoWPAN is made up of the interfaces of LoWPAN Nodes and Edge Routers sharing the same subnet prefix. Due to the non-transient nature of 6LoWPAN links, IP routing may be used on the link to provide transitivity. This exhibits a multi-link subnet feature with regard to hop limit as defined in [RFC4903], and thus 6LoWPAN applications should make no assumptions about the hop limit as it may be decremented in a LoWPAN. -- http://www.sensinode.com http://zachshelby.org - My blog "On the Internet of Things" Mobile: +358 40 7796297 Zach Shelby Head of Research Sensinode Ltd. Kidekuja 2 88610 Vuokatti, FINLAND This e-mail and all attached material are confidential and may contain legally privileged information. 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