ORBIT: Location-based services

Henning Schulzrinne

Columbia University

Location-based services Finding services based on location

physical services (stores, restaurants, ATMs, …) electronic services (media I/O, printer, display, …) not covered here

Using location to improve (network) services communication

incoming communications changes based on where I am configuration

devices in room adapt to their current users awareness

others are (selectively) made aware of my location security

proximity grants temporary access Privacy rules for access to context data

Location-based services & SIP We’re using SIP (and SIMPLE) as generic protocols

for effecting change (“actuators”)

send MESSAGE to devices distributing event information (“sensors”)

Advantages: people and rooms identified by URIs

sip:hgs@cs.columbia.edu sip:cepsr815@cs.columbia.edu

cross-domain, with extensive security mechanisms domains don’t need to trust each other

scalable to global system many other systems are mostly local

Location-based services Presence-based approach:

UA publishes location to presence agent (PA) becomes part of general user context other users (human and machines) subscribe to context

call handling and direction location-based anycast (“anybody in the room”) location-based service directory

Languages for location-based services building on experience with our XML-based service

creation languages CPL for user-location services LESS for end system services

Location information

geospatial longitude, latitude, altitude

civil time zone, country, city, street, room, …

categorical type of location properties of location

privacy (“no audio privacy”) suitability for different communication media

Determining location

GPS may not be practical (cost, power, topology)

Add location beacons extrapolate based on distance moved

odometer, pedometer, time-since-sighting idea: meet other mobile location beacons

estimate location based on third-party information

PA

devicecontroller

SUBSCRIBEto each room

SUBSCRIBE to configurationfor users currently in rooms

1. discover room URI2. REGISTER as contact for room URI

tftp

HTTP

Example: user-adaptive device configuration

SLP

“all devices that are in the building”RFC 3082?

802.11 signal strength

location

REGISTERTo: 815cepsrContact: alice@cs

SIP

room 815

Architectures for (geo) information access Claim: all using protocols fall into one of these categories Presence or event notification

“circuit-switched” model subscription: binary decision

Messaging email, SMS basically, event notification without (explicit) subscription but often out-of-band subscription (mailing list)

Request-response RPC, HTTP; also DNS, LDAP typically, already has session-level access control (if any at all)

Presence is superset of other two

Presence/Event notification Three places for policy enforcement

subscription binary only policy, no geo information subscriber may provide filter could reject based on filter

(“sorry, you only get county-level information”) greatly improves scaling since no event-level checks needed

notification content filtering, suppression only policy, no geo information

third-party notification e.g., event aggregator can convert models: gateway subscribes to event source,

distributes by email both policy and geo data

Presence model

subscriptionpolicy

event generatorpolicy

subscriberfilter

rate limiter

change to previousnotification?

for eachwatcher

subscriber (watcher)

SUBSCRIBE

NOTIFY

Policy rules

There is no sharp geospatial boundary Presence contains other sensitive data

(activity, icons, …) and others may be added Example: future extensions to personal

medical data “only my cardiologist may see heart rate, but

notify everybody in building if heart rate = 0” Thus, generic policies are necessary

Processing models

Sequential model: for each subscriber, apply rules to new data doesn’t scale well to large groups

Relational database model: re-use indexing and other query optimizations well-defined query and matching semantics e.g., mySQL and PostGres have geo extensions At time of subscription:

SELECT address FROM policies WHERE person=$subscriber (AND now() between(starttime,endtime) OR starttime is null) AND (a3=$a3 or a3 is null) …