Re: [Geopriv] Web-based DHCP location encoder

From: Richard Barnes ^lt;>
Date: Wed Apr 15 2009 - 11:42:50 EDT

Count me in with the folks who think there needs to be some sort of
indicator as to which interpretation is being communicated. Attaching
two different semantics to the exactly the same set of bits is the
definition of non-interoperability.

Looking at the 3825 format, it seems that the "datum" field is the only
one where there's any chance of accommodating this indicator. Defining
a single new datum is one way of doing it. Another way might be to
split the field half: A 4-bit datum field (do we need more than 31
data?) and 4 bits of flags (one for this, and three for later use).

+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
| Datum | ---> | Flags | Datum |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+

If you add the caveat that all flags being zero indicates the use of the
3825 encoding, this remains bitwise backward-compatible with 3825 (since
a 3825 server will set all flags to zero).


Thomson, Martin wrote:
> You'll note that the page clearly shows the two interpretations of RFC 3825. If you zoom to show the area described by the option and toggle the 3825bis checkbox, you'll see how these differ. In particular, note the difference when the point is near the edge of the box drawn using the (not bis) 3825 interpretation.
> Richard: The encodings are the same, only the interpretation differs.
> s/Alternate encoding/Alternative interpretation/
>> -----Original Message-----
>> From: [] On
>> Behalf Of Richard Barnes
>> Sent: Wednesday, 15 April 2009 8:58 AM
>> To: 'GEOPRIV'
>> Subject: [Geopriv] Web-based DHCP location encoder
>> Hey all,
>> FYI: The daunting thing about the DHCP location options (for me at
>> least) has always been figuring out how to encode and decode them, so
>> with some help from the loc-imp list, I've written a web-based encoder
>> for the DHCP location options (RFC 3825 and 4776):
>> <>
>> (Actually, the decoding logic is there too, in the Javascript objects,
>> but there's no GUI for it now.)
>> Hopefully, this can be at least a basic tool to ease people into
>> deploying this stuff. Please forward to anyone who might find this
>> useful.
>> Cheers,
>> --Richard
>> _______________________________________________
>> Geopriv mailing list
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Received on Wed, 15 Apr 2009 11:42:50 -0400

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