Transcript HELD

HELD
Location Acquisition Solution
James Winterbottom
Andrew Corporation Nov 2006
HELD Background
• Based on real-world requirements stemming from work
in NENA and other standards bodies.
• Provides an application layer location acquisition
protocol not restricted to SIP
• Respects requirements laid out in RFC-3693
• Demonstrated applicability to residential broadband
deployments
• Recognizes that location requires a solution that
operates above layer 3, can support SIP but is NOT SIP
specific.
• Defines a message exchange protocol for location
information. Different bindings can be used, HTTP is
described in the HELD draft.
– BEEP exists but not specific as an Internet draft at this time.
Basic HELD
• Very Simple!
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HTTP GET to a URL.
Server-side certificate
Determination based on source IP address.
Security provided through TLS and return routability
Location provided as a PIDF-LO
• LIS discovery through:
– Provisioning
– DHCP discovery (draft-winterbottom-geopriv-held-dhcp-discovery-00)
– DNS discovery through reverse DNS and U-NAPTR
(draft-thomson-geopriv-held-unaptr-00)
HELD Differentiators
• Supports requesting location in the form
required by an application.
• Supports a response time indicator,
CRITICAL in applications where more
than one determination technique is
available.
– Almost all mobile networks today offer more
than one location determination technique.
HELD Differentiators (cont)
• Supports Target identity extensions
(draft-winterbottom-geopriv-held-identity-extensions-00)
– necessary where target terminal correlators
change through a network (e.g. DSL).
• Supports Target to LIS location capability
exchanges (draft-thomson-geopriv-held-capabilities-00)
– Necessary to make best use of Target based
measurements.
Context and Reference Support
• HELD supports references by creating a
context on the LIS.
• When a context is created the Target
receives 1 or more URI types that can be
used to access the Target’s location.
– SIP or HTTP
• Context is controlled by Target, not kept
open for a pre-determined by the LIS.
HELD Identity Extensions Example
locationRequest(E)
IP->E -> D -> C -> B -> A -> Location
E
ISP
Gateway
LIS
RBP
Primary
LIS
IP + E
C+D
ALE
ALE
E
D
C
B
A
DSLAM
End-Point
Location
ISP
Network Access Server
(NAS)
Broadband Remote
Access Server
(BRAS)
HELD Device Capabilities
• Often a device can assist in determining or is
capable of providing its own location
– Timing and signal strength measurements
– Satellite pseudo-range measurements
– Autonimous location determination
• Where a LIS is deployed in a network it may be
useful to share determination capabilities
between the Target Device and the LIS.
– improvements in yield
– More precise location information
– Reduced time to obtain location
HELD Device Capabilities
• Two basic
mechanisms
– Device specifies
capabilities to LIS, LIS
responds with
supported capabilities
– LIS indicates to device
what capabilities it can
provide
Target
Device
LIS
createContext (Capabilities A, B ,C)
contextResponse (Capabilities A)
Target
Device
LIS
createContext ()
contextResponse (Capabilities A)
Device to LIS capabilities
Exchange
Serving
station
Station-1
Signal
Strength
Request Power
Measurements
S1=2, S2=3, S3=5, S4=1
Signal
Strength
Signal
Strength
Signal
Strength
Station-2
Station-3
Station-4
LIS
LIS to Device Capabilities
Exchange
Target Field of View
SV-5
SV-3
SV-9
SV-7
SV-1
SV-2
Access
Point
LIS knows Device
LIS knows Access point
LIS Calculates assistance data
Request GNSS Assistance
Look for SV-2, SV-3, SV-7, SV-9
AP-A
AP-B
LIS
HELD Implementations
Open Source Client
http://sourceforge.net/projects/held-location
Civic Address Display
Geodetic Location Display
Client Capabilities
• Supports all functions of HELD
specification
• Provides API to applications running on
the same PC. 1 Client for multiple
applications.
• LIS discovery through:
– DHCP
– DNS reverse lookups and SRV records
– Configuration
Open Source LIS
• Supports most of the HELD functionality.
– Initial implementation by second year engineering
student in 2.5 weeks.
– EASY TO IMPLEMENT!
• Latest version supports multiple Location
determination functions full, geodetic and civic
assertion, HELD identity extensions.
– To be posted sometime after the 17th of Nov.
• Basic provisioning interface provided
• Standalone/Proxy-LIS implementation in
OpenWRT Linksys wireless router available.
Open Source LIS Provisioning