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! – 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
RBPPrimary
LIS
DSLAM
ISPGateway
LIS
ISPNetwork Access Server
(NAS)
Broadband Remote Access Server
(BRAS)
End-Point Location
ABCE D
E
IP + E
IP->E -> D -> C -> B -> A -> Location
C + D
ALE ALE
locationRequest(E)
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
LIS
TargetDevice
createContext (Capabilities A, B ,C)
contextResponse (Capabilities A)
LIS
TargetDevice
createContext ()
contextResponse (Capabilities A)
Device to LIS capabilities Exchange
Serving station
LIS
Request Power Measurements
Station-1
Station-2
Station-3
Station-4
SignalStrength
SignalStrength
SignalStrength
SignalStrength
S1=2, S2=3, S3=5, S4=1
LIS to Device Capabilities Exchange
LIS
AccessPoint
AP-A
AP-B
Request GNSS Assistance
LIS knows DeviceLIS knows Access pointLIS Calculates assistance data
SV-1SV-2
SV-3SV-5
SV-7
SV-9
Look for SV-2, SV-3, SV-7, SV-9
Target Field of View
HELD ImplementationsOpen 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