Re: [Autoconf] Autoconf addressing model

"Stan Ratliff (sratliff)" <sratliff@cisco.com> Wed, 04 March 2009 21:35 UTC

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Date: Wed, 4 Mar 2009 16:35:22 -0500
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From: "Stan Ratliff (sratliff)" <sratliff@cisco.com>
To: "Alexandru Petrescu" <alexandru.petrescu@gmail.com>
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Subject: Re: [Autoconf] Autoconf addressing model
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> -----Original Message-----
> From: Alexandru Petrescu [mailto:alexandru.petrescu@gmail.com] 
> Sent: Wednesday, March 04, 2009 12:29 PM
> To: Stan Ratliff (sratliff)
> Cc: Charles E. Perkins; autoconf@ietf.org
> Subject: Re: [Autoconf] Autoconf addressing model
> 
> Stan Ratliff (sratliff) a écrit :
> > First off, you *can't* arbitrarily limit subnets to 25m. 25m from 
> > what? The center?
> 
> Yes, an area of 25meters with a wifi access point in the center.

*By definition*, what you describe is not a MANET. As you state, that's just a WiFi access point. That's already solved -- 802.11 clients can roam from access point to access point. But again, this should not be an 802.11-centric discussion. 

> 
> > And, how do you designate the center? Do you constantly 
> re-calculate  
> > the center based on movement?
> 
> No, not constantly re-computed.  But have a fixed view at a 
> point in time.  Saying everything varies isn't helpful either.
> 

It may not be helpful, but it's reality. You can't rely on a fixed view of a dynamic network; again, by definition, there's movement in a MANET. Links come and go, and link quality varies from moment to moment.


> > Also, from a radio perspective, how do you tell how far 
> apart you are  
> > in the first place? Do you suppose that all radios have 
> GPS? That's a 
> > non-starter, because GPS signals aren't always available.
> 
> No I didn't suppose GPS is available on each device, it 
> wouldn't work well under foliage.  Just a rough evaluation of 
> a specific link-layer radio range, correspondign to widely 
> used networks.
> 
> > And what about the wired MANET case brought up by Christopher 
> > Dearlove? Should we limit the cable runs?
> 
> YEs, certainly.  All cabled link-layers have specific 
> limitations on their lengths: 2m USB, 50m Ethernet Category6 
> (IIRC) and so on.
> 
> > I could understand (but
> > wouldn't really like) the notion of limiting the discussion 
> to links 
> > that are transitive; but placing some arbitrary distance 
> limit that's 
> > based on 802.11 just doesn't cut it for me.
> 
> 802.11 is being used widely, no reason to ignore.

I'm not advocating we "ignore" 802.11, or any other L2 technology, for that matter. I'm advocating that we remain Layer 2 agnostic. As Teco mentioned in another email, there are people in this WG that don't deploy MANET networks based on 802.11, or 802.16, or 802.15.4.

> 
> I'd happily accept to add another specific limitation, from 
> the link-layer of your choice.  And be speecifically 
> addressing these two link layers.  And maybe three.  No more 
> than three.
> 
> I find addressing them all to be difficult for me.

I don't understand why the Layer 3 addressing scheme needs to be predicated on a specific Layer 2 technology, or set of technologies. The Layer 3 addressing scheme should be totally independent of Layer 2 -- isn't that what layering is all about?

> 
> (about single point of failure being destroyed by a falling tree:
>   problem could be addressed at its layer: don't move the 
> command center
>   under trees risking falling); or maybe have two command centers, but
>   specificllay two, not an arbitrary large unknown number.
> 

That essentially boils down to "if it hurts, don't do it", and it doesn't work for my customers. Their environments are dynamic, and they need the ability to respond to ever-changing realities on the ground. 

At this point, I feel that we're in a discussion that is becoming more and more circular, and therefore, dysfunctional. And that, IMO, has been the unfortunate reality of this WG since its inception. 

Regards,
Stan


> Alex
>