Hi Chris,
OK, it makes sense. So the policy will be:
- the SOURCE_ROUTE TLV won’t have any value - Every TC message originated by the source-route supported routers will have a SOURCE_ROUTE TLV - The TC message not containing any neighbour address will have a longer validity time compared to OLSRv2 normal TC messages.
best
Jiazi
Additional comments >>> below. What I'm proposing (spelled out a bit more) is all win, and removes problems with the current design. I think this is a must do.-- Christopher DearloveSenior Principal EngineerBAE Systems Applied Intelligence Laboratories__________________________________________________________________________T: +44 3300 467500 | E: chris.dearlove@xxxxxxxxxxxxxxBAE Systems Applied Intelligence, Chelmsford Technology Park, Great Baddow, Chelmsford, Essex CM2 8HN.www.baesystems.com/aiBAE Systems Applied Intelligence LimitedRegistered in England & Wales No: 01337451Registered Office: Surrey Research Park, Guildford, Surrey, GU2 7YP-----Original Message-----From: Jiazi Yi [mailto:ietf@xxxxxxxxxxx] Sent: 09 May 2017 23:49To: Dearlove, Christopher (UK)Cc: ietf@xxxxxxxx; IETF-Announce; manet@xxxxxxxx; draft-ietf-manet-olsrv2-multipath@xxxxxxxx; manet-chairs@xxxxxxxxSubject: Re: [manet] Last Call: <draft-ietf-manet-olsrv2-multipath-12.txt> (Multi-path Extension for the Optimized Link State Routing Protocol version 2 (OLSRv2)) to Experimental RFC----------------------! WARNING ! ---------------------- This message originates from outside our organisation, either from an external partner or from the internet.Consider carefully whether you should click on any links, open any attachments or reply.Follow the 'Report Suspicious Emails' link on IT matters for instructions on reporting suspicious email messages.--------------------------------------------------------Hi Chris, Thanks a lot for the comments! Please check our reply inline: On 9 May 2017, at 12:13, Dearlove, Christopher (UK) <chris.dearlove@xxxxxxxxxxxxxx> wrote:
A few comments on this draft.
IPv6 specifies complete source routing. But this specification can only consider what happens within the MANET. So for a packet from somewhere in the MANET to somewhere well outside the MANET, the packet must be source routed to the gateway between MANET and rest of Internet, and not source routed after that. This I think should be explicitly mentioned. Whether that is considered compliant with IPv6 I leave to others.
Good point. We added some text at the end of section 8.4" Datagram Processing at the MP-OLSRv2 Originator"
7.1 SR_addr would better say "originator" address rather than
"network" address. (That makes it an address without a netmask, see
RFC 7181.)
fixed.
8.1 This is suggesting creating TC messages that have on neighbour addresses but have only a SOURCE_ROUTE TLV. This is not the design I would have suggested as consistent with how I would expect an extension to OLSRv2 to do things. We need to consider two kinds of routers: those sending TC messages anyway, those that (other than this extension) do not. In the former case you could just add the SOURCE_ROUTE TLV to those TC messages it sends. Then that information is maintained up to date. Routers that don't usually send TC messages could send TC messages with just that TLV. But then there's an issue over validity time. A parameter SR_HOLD_TIME_MULTIPLIER is introduced. There's no need for that - you can simply incorporate that into the validity time recorded in the message. That avoids a need to handle the two cases of routers differently. There is then an oddity that you get some routers sending TC messages with normal validity times and addresses, and some that can be sent less frequently with no addresses and longer validity times. But that's suspect - note that it's not done in OLSRv2 for attached networks (another reason to send TC messages although no neighbours need reporting). That's because longer intervals make reacting to new routers joining (and network reassembly after fragmentation) slow.
Rather a better design would simply be to add SOURCE_ROUTE TLV to normal TC messages. When sending TC messages for just that reason, that could be just the usual case, but you could allow as an option in this case to send less frequently with validity time increased accordingly. When not using that option, once a router needs to send a TC message, it could then decide to report neighbours, increasing the topology distributed and allowing more routes, this also being an option.
IIRC, we had a long discussion on this issue and produced the current text. The purpose is to identify the routers that don’t send TC messages but support source routing. To avoid unnecessary TC flooding, the interval is much longer than the normal TC interval. The normal TC messages (generated based on RFC7181) always have a SOURCE_ROUTE TLV. But if we use the same validity time for both RFC7181 normal TC processing and MP-OLSRv2 SR_ROUTE TLV processing, the valid time in the SR-OLSRv2 Router Set would be much shorter than expected. A possible case is that, the router stops sending normal TC messages, the corresponding entry in the SR-OLSRv2 Router set will soon expire. Therefore, I think it’s reasonable to make use of the SR_HOLD_TIME_MULTIPLIER to distinguish the valid time of normal TC message information and SR_ROUTE information. I don't agree, and I think what you are suggesting introduces a problem and unnecessary overhead.
The problem is that everywhere in OLSRv2 we are careful to ensure that parameters can be independently set, and that routers don't need to coordinate to interoperate. (They may do better if they do, but that's a refinement.) Here you are using an SR_HOLD_TIME_MULTIPLIER that the receiver has to know is what the sender intends. And it's unnecessary. If all that's in the TC message is the SOURCE_ROUTE TLV, you can just give that a longer validity time, because the only thing that validity time will impact on is the source routing status. If the router is also sending normal TC messages and you send separate SOURCE_ROUTE TLV TC messages then that would still be so. But that's inefficient, because if the router is already sending TC messages, why send separate ones with added overhead, when you can put the SOURCE_ROUTE TLV in the same TC message? That would then (without SR_HOLD_TIME_MULTIPLIER, but that's a good thing because SR_HOLD_TIME_MULTIPLIER is not good) give a shorter validity time to the SOURCE_ROUTE TLV, but that's fine, because that router will be sending more TC messages within that timescale anyway. Furthermore, this also allows the router that's sending TC messages more frequently to provide its information more responsively in the cases of nodes joining and networks reassembling.
That gives two behaviours: routers sending TC messages anyway, just add a SOURCE_ROUTE TLV, and routers not sending TC messages otherwise, just include a SOURCE_ROUTE TLV and set the validity time according to what schedule that router chooses to use - which can be at the same rate as the other routers, or at a slower route, or (a new capability you don't have) slowly, except if you learn of the existence of a new router in the network you can send one or more responsive SOURCE_ROUTE TLV only TLVs to enable that new router (or routers) to learn of the source routing quicker.
It's all win: combining messages, source set control, ability to do more clever things if you want to. (You could probably even still send separate TC messages with a SOURCE_ROUTE TLV when also sending normal TC messages if you really wanted to, as an option I can't see wanting to use - although it might introduce a minor problem that I haven't worked through the OLSRv2 specification to check, because it's unnecessary.)
The point is that what I suggest can gain everything you do, and allow more, plus not breaking expected OLSRv2 behaviour.
8.3 second bullet. You should here (and possibly elsewhere) exclude routers with routing willingness zero.
8.3 there seems to be an inconsistency. When operating proactively and no multiple routes, drop the packet, but reactively use standard routing. The latter seems more appropriate in the former case also.
9 CUTOFF_RATIO. Insists of strictly, but as defined earlier, may be >= 1`.
All fixed. Thanks again for the valuable comments!bestJiazi
--
Christopher Dearlove
Senior Principal Engineer
BAE Systems Applied Intelligence Laboratories
______________________________________________________________________
____
T: +44 3300 467500 | E: chris.dearlove@xxxxxxxxxxxxxx
BAE Systems Applied Intelligence, Chelmsford Technology Park, Great Baddow, Chelmsford, Essex CM2 8HN.
www.baesystems.com/ai
BAE Systems Applied Intelligence Limited Registered in England & Wales
No: 01337451 Registered Office: Surrey Research Park, Guildford,
Surrey, GU2 7YP
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Subject: [manet] Last Call: <draft-ietf-manet-olsrv2-multipath-12.txt>
(Multi-path Extension for the Optimized Link State Routing Protocol
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Abstract
This document specifies a multi-path extension for the Optimized Link
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