Hi, Would 'non-reflexive' (better called 'irreflexive') reachability mean that a node can not reach itself? If so... I think the term still makes sense, because 6LoWPAN nodes usually cannot send and receive at the same time (except if they had two physical radio interfaces).
By the way, typo: assymetric -> asymmetric. Greetings, Dominik On Tue, May 12, 2009 at 11:53 AM, Burnett, Peter <[email protected]> wrote: > 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. If you are not the intended recipient, > please contact the sender and delete the e-mail from your system without > producing, distributing or retaining copies thereof. > _______________________________________________ > 6lowpan mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/6lowpan > > The information contained in this message may be confidential and legally > protected under applicable law. The message is intended solely for the > addressee(s). If you are not the intended recipient, you are hereby notified > that any use, forwarding, dissemination, or reproduction of this message is > strictly prohibited and may be unlawful. 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