Re: Adding GPS location to IPv6 header

[William Herrin <bill () herrin us>]

On Mon, Nov 26, 2012 at 10:20 AM, Eugen Leitl <eugen () leitl org> wrote:
> On Mon, Nov 26, 2012 at 12:56:52PM -0200, Carlos M. Martinez wrote:
> > Just for redundancy's sake: No, L3 is **not** the place for this kind of
> > information. L3 is supposed to be simple, easy to implement, fast to
>
> I agree. You need to put it into L2, and the core usage would
> be for wireless meshes. Consider cases like Serval or cjdns,
> which run on Android headsets and equivalent embeddeds.
> Technically you wouldn't need GPS everywhere if you could
> do ~m scale time domain reflectometry in free space.
> It is possible to build a local contiguous map via
> mutual time of flight triangulation (actually, just visibility
> gives you a very good hint).

Actually, I think you just articulated the first use for Ammar's idea
that's not either wrong, absurd on its face or obviously better
handled at a different location within the protocol stack.

Suppose you have a large single-owner mesh network, such as a folks
walking around with cell phones. If you want them to have a stable
layer 3 address (and you do) then you're handling what amounts to /128
routes for tens of millions of devices. If you can guarantee that any
packet *to* that address also contains a rough geographic location
then you can discard any routes internally once they're more than a
short geographic distance from the origin and route on the geography
until you're close enough to find a specific /128 route. Tens of
millions of routes is no problem if no single router needs to know
more than a few thousand of them.

By putting geographic location at layer 3, you're also handling it end
to end which means you don't need a stateful border device to track
the current location of all of those /128 routes. The device itself
doesn't need to add location if it doesn't have the data; it's good
enough for the receiving tower to attach a rough location.

There are some assumptions in this model which are problematic. Key ones are:

1. Only valid as an interior gateway protocol (IGP). Geographic
routing has been proven false for an EGP because it induces traffic to
cross links for which neither source nor destination has permitted
access.

2. Requires the application at the landed end to copy the IP option
information into the outbound packets as well. This behavior is not
presently guaranteed.

3. Assumes that the device will originate communication, receiving
only replies from the landed end, or will use some intermediary to
communicate current geographic information if inbound origination is
required.


At any rate, I think that discussion of adding a geographic option
header to IPv6 should be tied up in the discussion of a routing
protocol which critically depends on its presence and can't reasonably
be built another way. Otherwise when a needful use case finally comes
along, you'll discover that the option's rules of operation don't
adequately enable it.

Regards,
Bill Herrin



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William D. Herrin ................ herrin () dirtside com  bill () herrin us
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