draft-ietf-geopriv-binary-lci-00.txt   draft-ietf-geopriv-binary-lci-01.txt 
GEOPRIV J. Schnizlein GEOPRIV J. Schnizlein
Internet-Draft M. Linsner Internet-Draft M. Linsner
Expires: July 1, 2007 Cisco Systems Intended status: Informational Cisco Systems
December 28, 2006 Expires: June 10, 2008 December 10, 2007
Binary to Decimal Conversion for Location Configuration Information Binary to Decimal Conversion for Location Configuration Information
draft-ietf-geopriv-binary-lci-00 draft-ietf-geopriv-binary-lci-01
Status of this Memo Status of this Memo
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This Internet-Draft will expire on July 1, 2007. This Internet-Draft will expire on June 10, 2008.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006) Copyright (C) The IETF Trust (2007)
Abstract Abstract
This document describes the nature of the data expressed in the geographic This document describes the nature of the data expressed in the
LCI defined in RFC 3825, and includes examples of conversion from its geographic LCI defined in RFC 3825, and includes examples of
binary format to decimal character strings. conversion from its binary format to decimal character strings.
Table of Contents Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Programming Hints . . . . . . . . . . . . . . . . . . . . . 3 5. Programming Hints . . . . . . . . . . . . . . . . . . . . . 4
6. Calculation of LCI values . . . . . . . . . . . . . . . . . 5 6. Calculation of LCI values . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . 6
8. Security . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. Security . . . . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1 Normative References . . . . . . . . . . . . . . . . . . 6 9.1 Normative References . . . . . . . . . . . . . . . . . . 7
9.2 Informative References . . . . . . . . . . . . . . . . . 6 9.2 Informative References . . . . . . . . . . . . . . . . . 7
10. Author's Address . . . . . . . . . . . . . . . . . . . . . . 7 10. Author's Address . . . . . . . . . . . . . . . . . . . . . . 7
A. Intellectual Property and Copyright Statements . . . . . . . 7
1. Terminology 1. Terminology
In this document, the key words "MUST", "MUSTNOT", "REQUIRED", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
"SHALL", "SHALLNOT", "SHOULD", "SHOULDNOT", "RECOMMENDED", "MAY", and NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
"OPTIONAL" are to be interpreted as described in RFC 2119 [1] and this document are to be interpreted as described in [0].
indicate requirement levels for compliant implementations.
2. Definitions 2. Definitions
This document uses the following terms to describe geo LCI binary to This document uses the following terms to describe geo LCI binary to
decimal conversion: decimal conversion:
Location Configuration Information: (LCI) An object that carries Location Configuration Information: (LCI) An object that carries
location information. LCI has no ability to express privacy rules as location information. LCI has no ability to express privacy rules as
outlined in [3] and [4], therefore is considered part of the 'sighting' outlined in [3] and [4], therefore is considered part of the 'sighting'
function. For purposes of this discussion, all references to LCI refer to function. For purposes of this discussion, all references to LCI refer
its use in [1]. to its use in [1].
GNU Compiler Collection: (GCC) The GNU Compiler Collection is a set of GNU Compiler Collection: (GCC) The GNU Compiler Collection is a set
programming language compilers produced by the GNU Project. of programming language compilers produced by the GNU Project.
3. Introduction 3. Introduction
The LCI encodes a point's latitude, longitude and altitude, along with the The LCI encodes a point's latitude, longitude and altitude, along with
resolution of that point. LCI does not encode boundaries of an arbitrary the resolution of that point. LCI does not encode boundaries of an
region. The resolution is nothing more than the representation of arbitrary region. The resolution is nothing more than the
significant digits for the fixed-length, binary values in the LCI. This representation of significant digits for the fixed-length, binary values
document corrects misinterpretations of the non-normative examples in [1]. in the LCI. This document corrects misinterpretations of the non-
normative examples in [1].
Format conversion is required between the binary LCI that a host can Format conversion is required between the binary LCI that a host can
receive through DHCP [1] or LLDP-MED [5] and the decimal representation receive through DHCP [1] or LLDP-MED [5] and the decimal representation
used by applications, e.g. PIDF-LO [2]. This conversion could be used by used by applications, e.g. PIDF-LO [2]. This conversion could be used
a host that provides its location to another party with the privacy rules by a host that provides its location to another party with the privacy
of the [2], including to a server authorized to redistribute the rules of the [2], including to a server authorized to redistribute the
information. It is unclear why anyone would need to convert from the information. It is unclear why anyone would need to convert from the
geographic-coordinate location format of [2] to the LCI. geographic-coordinate location format of [2] to the LCI.
4. Overview 4. Overview
This section provides an overview of the programming hints in the next This section provides an overview of the programming hints in the next
section for the translation from the efficient binary representation of section for the translation from the efficient binary representation of
the LCI [1][5] to the decimal string representation of geographic location the LCI [1][5] to the decimal string representation of geographic
used in PIDF-LO [2], for example. GCC syntax is used because it is well location used in PIDF-LO [2], for example. GCC syntax is used because
known. The binary values are converted to decimal, with the invalid bits it is well known. The binary values are converted to decimal, with the
removed and with the number of significant digits determined by the invalid bits removed and with the number of significant digits
resolution of the binary values. determined by the resolution of the binary values.
After unpacking the network-order bytes of the LCI into C variables After unpacking the network-order bytes of the LCI into C variables
sufficiently large to accommodate the fields, the sign bit of the two’s- sufficiently large to accommodate the fields, the sign bit of the two’s-
complement integers are extended to the size of the variable. The sign complement integers are extended to the size of the variable. The sign
bit at 34 bits to the left is tested with an octal constant containing 33 bit at 34 bits to the left is tested with an octal constant containing
bits in 11 octal-digits of zero. If negative, the sign is extended: the 33 bits in 11 octal-digits of zero. If negative, the sign is extended:
upper bits are set to ‘1’ by ORing the value with a value of minus-one the upper bits are set to ‘1’ by ORing the value with a value of
with the lower 34 bits inverted to zero with XOR. This operation is safe minus-one with the lower 34 bits inverted to zero with XOR. This
to perform more than once. operation is safe to perform more than once.
Because [1] says "Contents beyond the claimed resolution MAY be randomized Because [1] says "Contents beyond the claimed resolution MAY be
...", these contents are erased, i.e. set to zero. The number of bits to randomized ...", these contents are erased, i.e. set to zero. The
erase is the field length minus the resolution of the value in that field. number of bits to erase is the field length minus the resolution of the
A mask is constructed by left-shifting a one into the right of the mask value in that field. A mask is constructed by left-shifting a one into
for as many bits as to be erased. ANDing the inverse of the mask with the the right of the mask for as many bits as to be erased. ANDing the
value erases the invalid bits. inverse of the mask with the value erases the invalid bits.
The fixed-point fraction values are scaled into a floating-point (double The fixed-point fraction values are scaled into a floating-point
for enough precision) by dividing by the constant reflecting the number of (double for enough precision) by dividing by the constant reflecting the
fractional bits. Note that latitude and longitude have 25 bits of number of fractional bits. Note that latitude and longitude have 25
fraction, while altitude has only 22 bits. The number of significant bits of fraction, while altitude has only 22 bits. The number of
digits to the right of the decimal point is the resolution minus its significant digits to the right of the decimal point is the resolution
integer portion, scaled by 3 decimal digits for 10 binary digits because minus its integer portion, scaled by 3 decimal digits for 10 binary
10 to the 3rd = 1000 approximates 2 to the 10th = 1024. digits because 10 to the 3rd = 1000 approximates 2 to the 10th = 1024.
5. Programming hints 5. Programming hints
The LCI format is as follows: The LCI format is as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code 123 | 16 | LaRes | Latitude + | Code 123 | 16 | LaRes | Latitude +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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int64_t Latitude; /* Latitude 34 bits, 25 fractional */ int64_t Latitude; /* Latitude 34 bits, 25 fractional */
int8_t LoRes; /* Longitude Resolution 6 bits */ int8_t LoRes; /* Longitude Resolution 6 bits */
int64_t Longitude; /* Latitude 34 bits, 25 fractional */ int64_t Longitude; /* Latitude 34 bits, 25 fractional */
int8_t AltType; /* Altitude Type 4 bits */ int8_t AltType; /* Altitude Type 4 bits */
int8_t AltRes; /* Altitude Resolution 6 bits */ int8_t AltRes; /* Altitude Resolution 6 bits */
int64_t Altitude; /* Altitude 30 bits 22 bits Fraction */ int64_t Altitude; /* Altitude 30 bits 22 bits Fraction */
int8_t Datum; /* Datum code 8 bits */ int8_t Datum; /* Datum code 8 bits */
}; };
Because the latitude, longitude, and altitude values are twos complement Because the latitude, longitude, and altitude values are twos complement
of non-standard length, they require sign-extension that is not built into of non-standard length, they require sign-extension that is not built
typical variable types. For the Latitude into typical variable types. For the Latitude example:
example:
struct LCIoption OptIn; struct LCIoption OptIn;
/* if negative 34-bit field, set all one-bits above the 34-bit field */ /* if negative 34-bit field, set all one-bits above the 34-bit field */
if (OptIn.Latitude & 0100000000000LL) if (OptIn.Latitude & 0100000000000LL)
OptIn.Latitude = OptIn.Latitude | (-1 ^ 0177777777777LL) OptIn.Latitude = OptIn.Latitude | (-1 ^ 0177777777777LL)
/* XOR '^' to flip one bits to zero before ORing in the field */ /* XOR '^' to flip one bits to zero before ORing in the field */
Translation from the binary resolution of the LCI to the correct number of Translation from the binary resolution of the LCI to the correct number
significant decimal digits in the character string representation used for of significant decimal digits in the character string representation
numbers in PIDF-LO is as in the following example for used for numbers in PIDF-LO is as in the following example for Latitude:
Latitude:
int8_t eraseBits = 34 - OptIn.LaRes; int8_t eraseBits = 34 - OptIn.LaRes;
int64_t mask = 0LL; int64_t mask = 0LL;
if (eraseBits > 0) while (eraseBits--) mask = (mask << 1) | 1; if (eraseBits > 0) while (eraseBits--) mask = (mask << 1) | 1;
/* invert mask and AND to zero invalid bits */ /* invert mask and AND to zero invalid bits */
OptIn.Latitude &= ~mask; OptIn.Latitude &= ~mask;
double latitude = OptIn.Latitude / exp2 (25); double latitude = OptIn.Latitude / exp2 (25);
/* scale integer for 25 bits of fraction */ /* scale integer for 25 bits of fraction */
int8_t LatFractDigits = (OptIn.LaRes - 9) * 3 / 10; int8_t LatFractDigits = (OptIn.LaRes - 9) * 3 / 10;
/* deduct integer part, 2 to 10 ~= 10 to 3 */ /* deduct integer part, 2 to 10 ~= 10 to 3 */
if (LatFractDigits < 0) LatFractDigits = 0; if (LatFractDigits < 0) LatFractDigits = 0;
/* report integer part if resolution is lower */ /* report integer part if resolution is lower */
printf ("%11.*F\n", LatFractDigits, latitude); printf ("%11.*F\n", LatFractDigits, latitude);
6. Calculation of LCI values 6. Calculation of LCI values
Since the Global Positioning System (GPS) or survey methods do not provide Since the Global Positioning System (GPS) or survey methods do not
location in the LCI format, this section illustrates how a network provide location in the LCI format, this section illustrates how a
administrator might calculate the values in preparation for delivering network administrator might calculate the values in preparation for
them to hosts connected to her network. delivering them to hosts connected to her network.
Where geographic location is expressed with the correct number of Where geographic location is expressed with the correct number of
significant digits, it is easy to compute resolution because 3 decimal significant digits, it is easy to compute resolution because 3 decimal
digits approximate 10 bits. The number of digits to the right of the digits approximate 10 bits. The number of digits to the right of the
decimal point, times 10, divided by 3 is the number of fractional bits. decimal point, times 10, divided by 3 is the number of fractional bits.
Adding 9 for the integer part yields the resolution. Adding 9 for the integer part yields the resolution.
Where a geographic location comes with an explicit error specification, Where a geographic location comes with an explicit error specification,
this error can be translated into the resolution of the LCI. If the error this error can be translated into the resolution of the LCI. If the
measure is in distance (e.g. meters) rather than degrees, the conversion error measure is in distance (e.g. meters) rather than degrees, the
of longitude to degrees depends on the distance from the equator. conversion of longitude to degrees depends on the distance from the
Dividing the error distance by the distance for one degree (computed with equator. Dividing the error distance by the distance for one degree
the method described at [6]) yields the error in (presumably fractional) (computed with the method described at [6]) yields the error in
degrees. (presumably fractional) degrees.
double DegreeError; double DegreeError;
int64_t FixedPntErrDeg = degreeError * exp2 (25); int64_t FixedPntErrDeg = degreeError * exp2 (25);
/* convert error to fixed point 25-bit */ /* convert error to fixed point 25-bit */
int64_t TopBit = 0100000000000LL; int64_t TopBit = 0100000000000LL;
if (FixedPntErrDeg & TopBit) FixedPntErrDeg = - FixedPntErrDeg; if (FixedPntErrDeg & TopBit) FixedPntErrDeg = - FixedPntErrDeg;
/* if negative make positive */ /* if negative make positive */
/* shift test bit to find first non-zero error */ /* shift test bit to find first non-zero error */
int8_t resolution = 1; int8_t resolution = 1;
while ((FixedPntErrDeg & (TopBit >>= 1)) == 0LL) { while ((FixedPntErrDeg & (TopBit >>= 1)) == 0LL) {
if (TopBit == 0LL) break; if (TopBit == 0LL) break;
resolution++; resolution++;
} }
/* the shift count is the number of valid bits */ /* the shift count is the number of valid bits */
If all that is available is the bounding points of a region, the If all that is available is the bounding points of a region, the
difference between the extremes and the center in both latitude and difference between the extremes and the center in both latitude and
longitude estimates the error in degrees, which can be converted to longitude estimates the error in degrees, which can be converted to
resolution as above. Find the maximum and minimum of both, calculate the resolution as above. Find the maximum and minimum of both, calculate
value of the latitude/longitude as the average, and half the difference as the value of the latitude/longitude as the average, and half the
the error. difference as the error.
For the example bounds ranging about 0.5 meters in distances across about For the example bounds ranging about 0.5 meters in distances across
32 degrees, the binary and decimal values are as follows: about 32 degrees, the binary and decimal values are as follows:
binary decimal binary decimal
000011111.1111111111111111111001110 31.99999850 000011111.1111111111111111111001110 31.99999850
000100000.0000000000000000001011100 32.00000274 000100000.0000000000000000001011100 32.00000274
001000000.0000000000000000000101010 64.00000124 sum 001000000.0000000000000000000101010 64.00000124 sum
000100000.0000000000000000000010101 32.00000062 average 000100000.0000000000000000000010101 32.00000062 average
000000000.0000000000000000010001110 00.00000423 difference 000000000.0000000000000000010001110 00.00000423 difference
With 26 bits above the difference, which is twice the error, this example With 26 bits above the difference, which is twice the error, this
yields 27 bits of resolution (remembering to add 9 bits for left of the example yields 27 bits of resolution (remembering to add 9 bits for left
binary point). of the binary point).
7. IANA Considerations 7. IANA Considerations
No IANA Considerations No IANA Considerations
8. Security 8. Security
This document discusses binary to decimal conversion within an end host, This document discusses binary to decimal conversion within an end host,
which raises no particular security considerations. which raises no particular security considerations.
9. References 9. References
9.1 Normative References 9.1 Normative References
[1] RFC 3825 Dynamic Host Configuration Protocol Option for Coordinate- [0] RFC 2119 Key words for use in RFCs to Indicate Requirement Levels,
based Location Configuration Information. J. Polk, J. Schnizlein, M. S. Bradner. March 1997.
Linsner. July 2004.
[1] RFC 3825 Dynamic Host Configuration Protocol Option for
Coordinate-based Location Configuration Information. J. Polk, J.
Schnizlein, M. Linsner. July 2004.
[2] RFC 4119 A Presence-based GEOPRIV Location Object Format. J. [2] RFC 4119 A Presence-based GEOPRIV Location Object Format. J.
Peterson. December 2005. Peterson. December 2005.
[3] RFC 3693 Geopriv Requirements. J. Cuellar, J. Morris, D. Mulligan, [3] RFC 3693 Geopriv Requirements. J. Cuellar, J. Morris, D. Mulligan,
J. Peterson, J. Polk. February, 2004. J. Peterson, J. Polk. February, 2004.
[4] RFC 3694 Threat Analysis of the Geopriv Protocol. M. Danley, D. [4] RFC 3694 Threat Analysis of the Geopriv Protocol. M. Danley, D.
Mulligan, J. Morris, J. Peterson. February 2004 Mulligan, J. Morris, J. Peterson. February 2004
9.2 Informative References 9.2 Informative References
[5] TIA-1057 (LLDP-MED) The Telecommunications Industry Association [5] TIA-1057 (LLDP-MED) The Telecommunications Industry Association
(TIA) standard, "Telecommunications -- IP Telephony Infrastructure -- (TIA) standard, "Telecommunications - IP Telephony Infrastructure -
Link Layer Discovery Protocol (LLDP) for Media Endpoint Devices. Link Layer Discovery Protocol (LLDP) for Media Endpoint Devices.
[6] "Problem 2A.: Calculate path length along a meridian given [6] "Problem 2A.: Calculate path length along a meridian given
http://www.codeguru.com/Cpp/Cpp/algorithms/general/article.php/c5 http://www.codeguru.com/Cpp/Cpp/algorithms/general/article.php/c5
115 115
10. Author's Address 10. Author's Address
John Schnizlein John Schnizlein
Cisco Systems, Inc. Cisco Systems, Inc.
skipping to change at page 7, line 20 skipping to change at page 8, line 5
Email: john.schnizlein@cisco.com Email: john.schnizlein@cisco.com
Marc Linsner Marc Linsner
Cisco Systems, Inc. Cisco Systems, Inc.
Marco Island, Florida, USA Marco Island, Florida, USA
Email: marc.linsner@cisco.com Email: marc.linsner@cisco.com
Comments are solicited and should be addressed to the working group's Comments are solicited and should be addressed to the working group's
mailing list at geopriv@ietf.org and/or the authors. mailing list at geopriv@ietf.org and/or the authors.
Appendix A. Full Copyright Statement
Intellectual Property Statement Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at page 7, line 46 skipping to change at page 8, line 45
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment Acknowledgment
Funding for the RFC Editor function is currently provided by the Funding for the RFC Editor function is provided by the IETF
Internet Society. Administrative Support Activity (IASA).
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