Re: [homenet] Updates to Homenet Architecture Principles doc

[Alexandru Petrescu <[e-mail]>]

Le 14/06/2014 17:49, Juliusz Chroboczek a écrit :
>> So even though link-local multicast may be part of the IPv6 base spec,
>> it may be desirable to avoid use of multicast traffic where
>> possible. e.g. a routing protocol could perform initial neighbor
>> discovery using multicast, but then switch to unicast when maintaining
>> individual neighbor associations on the longer term, or for exchanging
>> information with specific neighbors.
>
> Ah, I see.  Yes, that makes sense.
>
>>> Then I think I don't understand what is meant by "multi-path support".  Is
>>> that merely the ability to switch to a better route if one becomes
>>> available?  Or is there something more to it?  Could you please clarify?
>
>> "The inclusion of physical layer characteristics including bandwidth,
>> loss, and latency in path computation should be considered for
>> optimising communication in the homenet."
>
>> I interpret the above text as requesting an ability to perform load
>> balancing over equal cost paths, potentially taking into account packet
>> loss and link quality when selecting which stream to send over which link.
>
> I don't.  I interpret that as meaning that the routing protocol should be
> able to pick a path using more refined criteria than just hop count.
> E.g. to prefer a 1Gb/s link to a 100Mb/s one, or to prefer two wired hops
> to a single wireless one.  Doing that is not too difficult, and yields
> dramatic performance improvements in some fairly simple, realistic
> topologies.

I agree.  We did that in a lab experiment with OSPF on 
Ethernet/Bluetooth/WiFi and by defining new metrics.

Alex


>
> Load sharing is a completely different headache.  Done carelessly, load
> sharing causes issues with increased latency and jitter, and causes
> intermittent connectivity problems that are very difficult to troubleshoot
> if one of the links is unreliable.  It also has ghastly performance if you
> balance across wireless links without taking radio interference into account.
>
> While it's certainly an area worth experimenting with, I'd be cautious
> about requiring load sharing in Homenet unless somebody knows how to do it
> right in the general unadministered case.
>
> -- Juliusz
>
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