Subject: RE: [mobile-ip] How about modification of DHAAD reply message?

From: "Ed Remmell" <[email-masked]>
Date: Thu, 5 Dec 2002 08:21:46 -0700

Jari -

I had earlier missed your "P.S." reply to my comment "broken algorithm for
an embedded systems implementation", but I noticed it today in the online
issue notes.

Yes, I agree, that statement I made was an exageration. Sub-optimal would
have been a better description. Also, I agree that this is a comparitively
minor specification issue, and since you are working on IETF last call, you
need to focus on the real problems. And, yes, I was just venting my
frustration at having to implement it the way it is currently defined ;-)
sorry.

Elmic Systems is an embedded systems TCP/IP protocol stack vendor. When
customers compare our products against competitors' products, they always
want to know about ROM code size. Every little byte helps. We are talking
about customers who want to see a complete TCP/IP protocol stack fit in 60K
bytes of ROM, less even. On a 32-bit big endian CISC processor like the
Motorola 68000, extra code is not as big a concern. But, put that same code
on a RISC processor (i.e. Motorola PowerPC, MIPS), and it gets 50% bigger.
Put it on a 16-bit or 8-bit processor, and it gets even bigger still.

So, any way to avoid exception cases and extra complexity which results in
extra code is very much appreciated. For example, current MN return to home
functionality is going to result in significant extra code to properly
handle the exception case where the MN still has active home address
bindings with the HA (and is possibly not even aware of that fact), but I
don't see any easy way around it short of turning the MN into a 2nd class
citizen w/ regards to not actively defending its home addresses when it
operates on a foreign link (which, I agree, isn't a great solution).

Thanks.
- Ed Remmell
Elmic Systems, USA
http://www.elmic.com

> -----Original Message-----
> From: Jari Arkko [mailto:[email-masked]]
> Sent: Tuesday, November 26, 2002 10:59 PM
> To: Pyungsoo Kim
> Cc: [email-masked]; Ed Remmell
> Subject: Re: [mobile-ip] How about modification of DHAAD reply message?
>
>
> Pyungsoo Kim wrote:
> > In the processing of DHADD reply message,
> > if a mobile node knows the number of HA's addresses, it can
> select easily
> > the HA's address according to preference. (because HA's addresses are
> > listed according to preference).
>
> I don't think it is wise to add redundant fields to protocol messages.
> We already know the length of the IP packet, from which you can calculate
> the number of HA addresses. If we add another length field, there'll
> be plently of error cases you'll need to deal with. In effect, you'll
> have to take in account the IP packet length anyway and in addition
> worry about the other length field.
>
> In short, I'll propose to reject this modification.
>
> Jari
>
> P.S. Ed: Some people - like me - agree with you that the optimization
> of omitting the responding HA's address adds some processing for a very
> small benefit. However, "broken for embedded implementations" is an
> exaggeration. The issue was decided earlier - lets move on, life continues
> even with a few additional lines of code. Let's worry about real problems
> instead.
>
>