Hi Jari, thanks for following up on this. If I understand correctly, the proposal is to develop recommendations for link layers to support inter-access handovers and flow mobility. I am not sure why link layer is the best way to handle this when we are in fact traversing disparate link layers. I would have thought extensions to Router Solicitations and Router Advertisements would be appropriate. Granted this is an extension to the host stack, but that should be made clear in an Applicability Statement. Anyway, this is missing an important piece: the LMA - MAG protocol interaction, assuming underlying support for what is necessary between MN and MAG. Without LMA - MAG protocol, we cannot do inter-tech handovers and flow mobility. We would need this regardless of how we solve the MN - MAG part.This should be included in the charter. Regards, -Rajeev ________________________________ From: netext-bounces at ietf.org on behalf of Jari Arkko Sent: Wed 10/21/2009 2:29 PM To: netext at ietf.org Subject: [netext] NETEXT2 BOF conclusion I have been trying to come up with a way forward on this, but its hard. To recap, there are a few different technical possibilities for multi-interface mobility: 1) Link layer hides interface variants behind one logical interface. For instance, an IP stack does not see the change from GSM to UMTS radio or 802.11b to 802.11g; its handled as a part of the link layer. Such link layer operations need to be supported both by the host and the network. This approach has the minimum impacts on IP stack, but requires specification of the link layer mechanisms across the used interfaces. 2) Different interfaces are handled via existing host-based mobility mechanisms (Mobile IPv6, MOBIKE, HIP, application layer). Within one interface the link layer handles mobility, possibly using Proxy MIP internally. Both the host and the network need to support the host-based mobility mechanism, but the link layer does not have to aware of the other interfaces in any way. 3) We extend Proxy MIP with capabilities to handle cross-interface handovers. This is similar to approach #1, but the signaling messages are at the IP layer. The benefit is that this could be used across different types of link layers even if they do not support handovers. The downside is that just as with approach #2, the IP stack has to be capable of these operations. The big argument we have been stuck with since San Francisco is between #2 and #3. One group believes that existing mechanisms are sufficient, and they are -- it is indeed possible to do this. Another group believes that they need a different solution based on Proxy MIP. Such a solution is also of course possible. But we've made very little headway in resolving the question on what should be done. In particular, we've not been able to describe very well why some technical reasons would dictate one or the other solution. I believe that is likely because they are really very similar solutions. At this point I do not believe we have consensus to go forward. We left the BOF with the idea that requirements work would solve this issue. If I'm right the solutions really are very similar, this work may not be able to resolve the conflict, and it would take a long time. I think it would actually serve as better if we were to decide now, as opposed to pretending that more details will make the decision easier. With this in mind, I have a proposal for a way forward. Given that I do not see consensus for approach #3, I do not think we can go ahead with that. I also personally believe that #2 and #3 are functionally similar enough that there's no requirement that forces us to pick #3. In addition, approach makes mobility end-to-end between the host and a network node; approach #3 ties the use of mobility to a particular link. If the router on that link does not support the mobility mechanism, mobility service is not possible. I think it would be architecturally better to separate access and mobility. However, I would like to move forward with a different work item. The IETF has never really explored approach #1, even if it is commonly used. Of course, the IETF's role is not to design these link layer mechanisms, but I believe it would be valuable for the IETF to publish an informational document on considerations for building such mechanisms. This document would talk about the requirements that the mechanisms must fulfill in order for IP to work correctly, when such mechanisms are recommended and when not, what their advantages and downsides are, what happens if MTUs or routers differ, and so on. At the same time this document would describe the "virtual link" model that some people have been using in the context of Proxy MIP. The idea is to add this work to the NETEXT WG charter. I realize this does not make everyone happy, but I'm not sure there is an outcome that does. What we lose by not doing solution 3 is a design that that simultaneously allows something to be done in a link-layer agnostic manner _and_ employs PMIP as a part of the solution. Thoughts? Jari _______________________________________________ netext mailing list netext at ietf.org https://www.ietf.org/mailman/listinfo/netext
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