Subject: [Ospf-manet] Re: Ospf-manet Digest, Vol 11, Issue 1

From: Aniket Desai <[email-masked]>
Date: Sun, 01 Oct 2006 16:40:23 -0400

At 02:22 PM 10/1/2006, [email-masked] wrote:
>Even if we go to experimental, it seems that only OR and OSPF-MPR would
>a priori fit. The MDR proposal would need to be very deeply reworked.
>Now it looks more like a patchwork of optional recipes, some of them
>unecessarily complex, none based on matured background or diversified
>experimentation. The draft as it is, seems to contain one hundred
>protocols and  the inflation will lilely continue as far as I understand.
>
>OR and OSPF-MPR show at least a unity and present clear solutions which
>can be exploited, and are based on elements that have already received
>considerable attention in the past.
>
>BTW if you fix the objective to synchronize all links, the MDR concept
>will loose any benefit.
>
>Best regards,
>Philippe

I am sorry, but having implemented OSPF-MDR in less than 3 months, I 
know this is simply not true. I agree that OSPF-MPRs are less complex 
than the MDRs on paper, but I am not really sure if that paper 
complexity can translate into actual algorithms. For example, the 
flooding algorithm is still O (n) and each hello reception results in 
the same amount of processing that would happen in OSPF-MDR (actually 
I have reason to believe that MPRs do more processing, as we did a 
quantify analysis on similar OSPF and OLSR networks). The only 
difference is that MPR selection algorithm have less overhead than 
distributed CDS of OSPF-MDR (NOT less complexity though, which is 
still O (n^2)). OPNET; for example; implements these algorithms using 
arrays, which is significantly cheaper than using DFS trees (as is 
done in Ogier draft). The point is that distributed CDS algorithms 
are not that heavy.

If we really compare both MDR and MPR approaches based upon their 
modules, I do not see much computational complexity differences. Can 
someone show otherwise?

I agree that if the objective was to fix all neighbors to be 
synchronized, then one can definitely use MPRs. It should be easily 
possible for us to do this in simulations and see what throughout we 
can get. I had simulated a 50 node *point to point* network with an 
average of 30 neighbors (dense connectivity), with minimal mobility. 
The throughput was 0. Using OSPF MDRs, nearly 90% throguhput was 
obtained. I would be happy to share these OPNET models. The only 
thing in the above experiment was that each node was doing the 
flooding, which can be corrected by plugging the MPR selection 
algorithm. In fact, I will do this by next weekend and post the 
results of my experiment here.

Sincerely,

Aniket 

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From: Aniket Desai <[email-masked]>
Date: Sun, 01 Oct 2006 17:07:57 -0400

At 02:22 PM 10/1/2006, you wrote:
>Being a sponge and absorbing other ideas until this last minute 
>makes the proposal
>look immature and not ready for standardization other than experimental
>and that was my point.

Forgive me for speaking on Dr. Ogier's behalf. It was simply said in 
response to the original post that multicasting retransmitted LSAs is 
not a *flaw* or a *patchwork* or *sponge absorbing other ideas* or 
<fill in the blanks>. This could have easily been added in draft 1 or 
in the final draft. I don't think it changes anything. 
Retransmissions are separate from core flooding, and any OSPF 
implementation, regardless of what it uses, can easily optimize 
existing retransmission mechanism. If someone else came out with that 
idea first, then he/she must be congratulated with great 
appreciation, but that is not a basis to say that MDR draft is 
immature. I have read MDR draft since its early versions (since the 
time when many distributed CDS algorithm families were explored), and 
I find it one of the most systematically written, well thought out 
and elegantly evolving draft.

In fact I found it rather nice that there was some exchange of ideas 
on WG and with a collective process, a better design emerged. This is 
what I really had in mind when I joined WG, and I won't hide the fact 
that I have learned a great deal simply by following the exchange on 
WG (however those days are long gone). What I find unfortunate is 
that the very ability of the MDR draft and its author to accept this 
process is being shown as a draft weakness. I thought it was a great 
thing that everyone was contributing their ideas to the MDR 
draft...but now is it really expected that MDR draft must be tip and 
top by so and so date and no more changes must be done to it henceforth???

Sincerely,

Aniket