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