Hi Robert:
Your +1 could be misinterpreted then... I think Carsten did. The flow label helps the router select the instance for a packet. It does not help a host that needs to select a router that serves that instance. A plain host (that does not support RPL) will need to find that in RAs. In a same fashion, it will need to place what it's looking for in RS (like we'll do in DIS). And the new ND registration will have to indicate into which instances the registration must be injected as a DAO. Do you agree so far? The DODAG ID is not the appropriate information for the host, unless it is concerned with DAG multihoming and such, which I would not expect. The router can and will switch DODAG within the instance and the host will not care, since its applications will be served either way. When the router leaves the instance entirely, then the node will care, and it needs to know. At worst, we can achieve that with a new unreachable code. Finally, a root might use the same DODAG ID in multiple instances. So the router could be confused if the host only indicated a DODAG ID... Still in agreement? On the side, we discussed for P2P about making local instances that actually depend on the DODAG ID so that the fully qualified instance ID would really be the tupple (DODAG ID, instanceID). That's still in limbo though I do think we need it. What's your take on this? Pascal From: Robert Cragie [mailto:[email protected]] Sent: Friday, May 07, 2010 1:41 PM To: Pascal Thubert (pthubert) Cc: Richard Kelsey; [email protected]; [email protected]; [email protected] Subject: Re: [Roll] [6lowpan] how does a node get an IP address Hi Pascal, I understand what you're saying and agree that in the case of multiple RPL instances, whereby each RPL instance is characterized by potentially different metrics (that's the point of them, right?), you would need some sort of qualification at the packet originator as to which RPL instance it ends up choosing for its route to its destination. This is done using the flow label. On the other hand, a DODAG is, as its name implies, a destination oriented DAG. Therefore the DODAG ID is the general discriminator within a RPL instance for which route a packet takes based on its destination. There is no need for any other additional information, surely? So that's what the +1 was for. The spec. seems a little confused on this anyway. In section 7.2 it says the RPLInstanceID field is an "8-bit field indicating the DODAG instance along which the packet is sent". But the DODAG instance is an instance within a RPL instance. Can you clarify this? In general, I find the instances confusing, as they are often considered as a tuple (RPLID, DODAGID, DODAGSeqNum). However, transitioning from (1,1,1) to (1,1,2) is not the same as transitioning from (1,1,1) to (1,2,1) and this is not clear in the specification. Robert Robert Cragie (Pacific Gas & Electric) Gridmerge Ltd. 89 Greenfield Crescent, Wakefield, WF4 4WA, UK +44 (0) 1924 910888 http://www.gridmerge.com <http://www.gridmerge.com/> On 07/05/2010 7:08 AM, Pascal Thubert (pthubert) wrote: Hi Robert and Richard: We designed instances to enable to support multiple sorts of traffic with different requirements. The instance is the network response to the application needs. The application resides in the host, even if routers sometimes play both roles. The application needs to signal the instance one way or another in its packets, and we use flow labels for that. So far so good. What's missing: The host also needs to join the RPL networks that support the instances that it needs. That must be signaled in the router to host interface. The host also needs to be advertised in the RPL networks that support the instances that it needs. That must be signaled in the host to router interface. >From there I think you've got the logic reverse: You're correct that ROLL supports a host with no RPL extension using instance 0 / flow label 0. But still the host to router interface needs to be augmented for an application residing on the host to benefit from ROLL instances. What I'm reading below is "a host MUST be a router in order to comply with the ROLL MUST of supporting multiple types of traffic". Well, -1. Pascal From: Robert Cragie [mailto:[email protected]] Sent: Thursday, May 06, 2010 7:48 PM To: Richard Kelsey Cc: Pascal Thubert (pthubert); [email protected]; [email protected]; [email protected] Subject: Re: [Roll] [6lowpan] how does a node get an IP address +1 Robert Cragie (Pacific Gas & Electric) Gridmerge Ltd. 89 Greenfield Crescent, Wakefield, WF4 4WA, UK +44 (0) 1924 910888 http://www.gridmerge.com <http://www.gridmerge.com/> On 06/05/2010 1:16 PM, Richard Kelsey wrote: Date: Thu, 6 May 2010 09:02:28 +0200 From: "Pascal Thubert (pthubert)" <[email protected]> <mailto:[email protected]> [Pascal] 6LoWPAN ND needs some addition to enable RPL aware hosts. In particular around instance IDs. Pascal, I disagree with "needs". The ability to select an instance ID for a particular message is an optional extra. RPL works fine without it. I am okay with limiting instance ID selection to routers. -Richard Kelsey _______________________________________________ Roll mailing list [email protected] https://www.ietf.org/mailman/listinfo/roll
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