Subject: RE: [SeaMoby] Topic #3: Cache contamination

From: [email-masked]
Date: Fri, 14 Mar 2003 13:03:17 -0500

Jim,
> Govind,
> 
> I'm not convinced Dycard would do any better.
[Govind] 
 The discussion in this thread had nothing to do with dycard.
It was discussing the cache management 
scheme you had proposed w.r.t to its applicability as a cache management
 scheme for the DT draft. I was merely pointing out that it has significant problems when
used in conjunction with the DT draft as it is now.

> 
> As the number of malicious MNs increases, the number of PNE 
> messages will
> increase. Thus, the load on the routers increases in any 
> event.

[Govind] I think you should read some of the old threads, where I have
pointed out how this can be handled. In short, we restrict entries per MN,
identified by its identity. Second, if an MN sends more than one RI message
it is clearly malicious and not the case with a MN sending more than one
APids as I have pointed out in my example in a previous email.  Note, 
I am not saying that you don't have to handle case of cache contamination
in dycard, I am just saying it can be handled differently and even the scheme 
that you proposed may work better with dycard than with the DT scheme, but
I haven't analysed it yet. The simple logic in dycard, using my previous example,
 is that if you have 10 colluding 
malicious MNs you would be able to create at max [10* (limit on entries per MN)] in the cache by
sending RIs. 
In our simulations, if you have a large number of MNs (which is there anyways) in the
system, limiting to just one entry per MN is quite good. 
The MNs would have to be able to show that they handed over from non-CARs.
This is quite difficult to achieve rather than how you populate caches in the
DT scheme, IMO. I think we are going in circles, as this was pointed out previously too. If  you read
the draft carefully and you don't think this has been explained well then we are willing to
address that and make it clearer.

 If there are
> several millions of malicious MNs bombarding the router with 
> RM messages, the
> backhaul will fill with PNE messages as far as I can tell. 

[Govind] RM messages don't launch PNEs. 

I 
> assume Dycard is
> using a cache for confirmed APs also, so that no PNE message 
> would be sent if
> the RM resulted in a hit with a known, good GAAP. Or am I 
> misunderstanding how
> Dycard works?

[Govind] I think you have a misunderstanding on how dycard works.
 PNE messages are sent
based on new AR reports in RI messages, provided the limit is not reached for the
reporting MN. PNEs have nothing to do with APs.

> 
> You mentioned previously you had done a simulation on this. 
> Could you or another
> of the Dyhard Dycard Team provide some information about what 
> the numbers look
> like, or a URL to a published paper?

[Govind]  A paper is under review. I don't think I can make a decision on my own to put it on
a webpage. 

-Govind.
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---

From: "James Kempf" <[email-masked]>
Date: Fri, 14 Mar 2003 11:10:49 -0800

Govind,

Metacomment: I am trying to understand Dycard, as, I presume, are others in the
WG. If you and the rest of your team want it or features of it to be included in
the protocol (which is why, I presume, you are arguing so strongly against the
DT draft) then you need to help us understand it. It is not helpful or
constructive to criticize someone else's work without providing a alternative.
From my reading of the Dycard draft, there may be some useful features in it, we
need to have the working group understand those.

Now, on to specific comments.

> [Govind] I think you should read some of the old threads, where I have

I did. Like I said yesterday, it was like a rugby match. Not very enlightening.
:-)

> address that and make it clearer.

So why can't the server scheme limit the number of entries per MN? Limiting the
number of entries per MN has nothing to do with the back end, where the router
finds out what is an authorized GAAP, which is where Dycard and the server
scheme differ as I understand it. It has to do with the front end, where the
router decides what to do with an incoming message.

> [Govind] RM messages don't launch PNEs.

I see from the draft that it is the RI message that launches PNE, my bad. Now,
please tell me why an MN can't bombard the router with RI messages? The router
can rate limit, as you mention above but, in your comments on the Issues, you
said that you didn't think rate limiting was an issue, so...? Is rate limiting
important or isn't it? I'm confused.

> reporting MN. PNEs have nothing to do with APs.

OK. What happens when the limit is reached? Wouldn't a cache (regardless of the
timeout policy) be necessary regardless?

> [Govind]  A paper is under review. I don't think I can make a decision on my
own to put it on

Fine. Please post a URL when the review is complete, so the WG can have a look.

            jak

---

From: "James Kempf" <[email-masked]>
Date: Fri, 14 Mar 2003 11:10:49 -0800

Govind,

            jak