SUPL was developed by the Open Mobile Alliance1 (OMA),
a mobile communications industry forum that was created to bring open
standards, platform independence, and global interoperability to the LBS
market. More than 360 companies are represented in OMA, including MNOs and
NEVs, wireless vendors, mobile device manufacturers, content and service
providers, and other suppliers. SUPL standards acknowledge Assisted GPS (AGPS)
as the most accurate location technology available today. SUPL architecture is
composed of two basic elements: a SUPL Enabled Terminal (SET) and a SUPL Location
Platform (SLP). The SET is a mobile device, such as a phone or PDA, which has
been configured to support SUPL transactions. The SLP is a server or network
equipment stack that handles tasks associated with user authentication,
location requests, location-based application downloads, charging, and roaming.
The core strength
of SUPL is the utilization, wherever possible, of existing protocols, IP
connections, and data-bearing channels. SUPL standards are complementary to and
compatible with C-Plane standards. SUPL supports C-Plane protocols developed
for the exchange of location data between a mobile device and a wireless
network, including RRLP3 and TIA-80144. SUPL also supports MLP (Mobile Location
Protocol) and ULP (UserPlane Location Protocol). MLP is used in the exchange of
LBS data between elements such as an SLP and a GMLC, or between two SLPs; ULP
is used in the exchange of LBS data between an SLP and an SET.
Implementation: SUPL vs.
C-Plane
Two functional entities must
be added to the C-Plane network in order to support location services: a
Serving Mobile Location Center (SMLC), which controls the coordination and
scheduling of the resources required to locate the mobile device; and a Gateway
Mobile Location Center (GMLC), which controls the delivery of position data,
user authorization, charging, and more. Although simple enough in concept, the
actual integration of SMLCs and GMLCs into the Control Plane requires
multi-vendor, multi-platform upgrades, as well as modifications to the
interfaces between the various network elements. As with any complex endeavor,
the larger the scope of the program and the more parties that are involved, the
greater the number of points at which failures can occur. LBS through SUPL is
much less cumbersome. The SLP takes on most of the tasks that would normally be
assigned to the SMLC and GMLC, drastically reducing interaction with Control
Plane elements. SUPL supports the same protocols for location data that were
developed for the C-Plane, which means little or no modification of C-Plane
interfaces is required.
AGPS for Location-Based
Services
The“A” in AGPS is the
assistance data provided to mobile AGPS devices through a wireless network.
With this data, mobile devices equipped with AGPS can compute positions more
quickly and in much more difficult environments. Traditional GPS receivers work
best in open areas that offer an unobstructed line of sight to the GPS
satellites orbiting overhead. In places where GPS signals are weak, obstructed,
or scattered, as is the case inside an office building or in an urban canyon,
traditional GPS receivers compute positions intermittently at best and
frequently cannot compute positions at all.
Call Flows
In the network-initiated and SET-initiated call flows detailed below, the
GMLC does nothing more than provide the initial position for the position
calculation sequence that is conducted between the SLP and the SET. The SLP and
the SET communicate through ULP, a binary protocol that supports eight basic
messages. These messages are used to initiate a SUPL session, exchange
positioning and authentication data, and end a SUPL session. Communication
between the SLP, the Client application, and the GMLC is done through MLP. Only
two MLP message types, SLIR (Standard Location Immediate Request) and SLIA
(Standard Location Immediate Answer), are used in either transaction sequence.
This is important because although MLP is very complex, utilization of MLP in
SUPL architecture is not.
Network
initiated request
Step 1. The Client application
queries for the location of the targeted SET by sending an SLIR message
(Standard Location Immediate Request) to the SLP. The message contains an ID
for the targeted SET, positioning preferences, routing information, and a
transaction code. The SLP authenticates the request and then determines whether
the transaction will be based on AGPS or another positioning resource.
Step 2. The SLP sends a SUPL INIT message to the targeted SET through SMS or WAP push. The message contains an access code, an address for the SLP, parameters for the positioning method that will be used, and a unique, SLP-generated Session ID.
Step 6. The GMLC authenticates the request, then queries its Cell ID
database to find the latitude and longitude of the Cell ID referenced in the
SLIR message. The latitude and longitude of the Cell ID will serve as the
initial position for the position calculation.
SET
initiated request
Step 1. The SET connects to an IP network through GPRS, EDGE, or other
means.
Step 6. The SLP sends a SUPL RESPONSE message to the SET, which identifies
the positioning method that will be used, and contains a unique Session ID that
is a combination of the Session ID generated by the SET and a Session ID
generated by the SLP. This compound Session ID will be used in all of the
remaining messages exchanged between the SET and the SLP. The SUPL RESPONSE
message may also contain an address for the SLP and authentication data if the
transaction requires authorization.
GLOSSARY
SET
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SUPL Enabled Terminal. A device that can communicate with a SUPL network.
Communication with the SUPL network is handled
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LBS
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Location-Based Services. An extension of LCS that includes a wide variety
of real-time services and takes advantage of burgeoning wideband wireless
communication services.
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LCS
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Location Services. A generic term for services and related applications
that are based on the geographic location of a mobile device, and are
channeled primarily through wireless communication networks.
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LSP
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Location Services Provider. A mobile network operator or SUPL provider
that manages location services for LBS subscribers.
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SLP
|
SUPL Location
Platform at the center of Figure 3 is responsible for all aspects of SUPL
communication between the SET and the rest of the SUPL-enabled network. The
SLP also provides all AGPS data services from the embedded AGPS Server
engine, including providing assistance data and performing position
computations.
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MLP
|
MLP is used in the exchange
of LBS data between elements such as an SLP and a GMLC, or between two SLPs.
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ULP
|
ULP is used in the exchange
of LBS data between an SLP and an SET.
|
SMLC
|
Serving Mobile Location Center (SMLC), which controls the coordination
and scheduling of the resources required to locate the mobile device
|
GMLC
|
Gateway Mobile Location Center (GMLC), which controls the delivery of
position data, user authorization, charging, and more.
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