Re: [Ospf-wireless-design] Design Team slides for IETF 63

Phil,

>Specifically, I don't see a clear winner on how to do backup/pushback
>relaying.  The ORs design requires an ack to be received by each
>adjacent neighbor for the flooded LSA while the MDRs design requires an
>ack or hearing a flood of the LSA to all covered neighbors.  The result
>is that ORs have more backup floods while MDRs have more retransmissions
>due to the loss of the first flooded LSA.  If the design team would like
>to compare these mechanism, I don't see any reason why the pushback
>mechanism is precluded from the MDR approach or the backup mechanism is
>precluded from the OR approach.
>
Actually, there is a simple modification of the MDR BackupWait mechanism
that requires all adjacent neighbors to ACK before a (Backup) MDR
suppresses flooding the LSA. (But non-adjacent neighbors only need to
be covered.) This results in more Backup MDR floods,
as you might expect, and fewer unicast retransmissions.
The overall effect is that overhead is increased, but delivery ratio
may also be improved in some scenarios.

Keep in mind that we need to compare the performance when partial
adjacencies are used.  Just because both approaches have similar
performance with full adjacencies does not mean they will have
similar performance with partial adjacencies.

I think the important thing is that any such borrowing of techniques
from the other draft should be justified in terms of improved
performance, and fortunately the GTNetS simulations make this possible.

The same goes if we want to merge mechanisms for differential Hellos
or learning 2-hop neighbor information.  But the MDR approach requires
learning 2-hop neighbor information from Hellos, and the differential
Hello protocol in the draft seems ideal for achieving this.

Richard

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