Paper 2: Todd D. Hodes and Randy H. Katz

Composable Ad-hoc Location-based Services for Heterogeneous Mobile Clients

Submitted for review, Wireless Networks Journal special issue, November 1997

This paper deals more with the network issues involved in environment-aware applications. An architecture is presented for automatic resource discovery and remote access.

Key components in the architecture

• Mobility: Seamless connectivity (based on mechanisms like Mobile-IP) is assumed while building the framework for location based services.
• Controllable objects: Objects like camera, printers etc should be accessible via a network (maybe through a computer) for building such a framework.
• Resource Discovery: A mobile user (i.e. the device held by the user), should be able to discover resources (like camera, printer etc) that are available nearby (i.e. in the current environment).
• Control mapping: It is reasonable to expect that the controls exported by the object does not match with the controls provided by an application running on the mobile device. Thus, a mechanism for mapping controls is required.

Mobility

Functionality of a mobile-IP like protocol for providing seamless connectivity is assumed.

Controllable Objects: Issues

• Aggregation: The granularity at which the objects can be controlled is an issue. For example, it may not be possible to export individual controls for every light in a building or even a room.
• Conflicts: How to handle conflicts if there are any. For example, one user may want a light to be dimmer than another user wants. Such conflicts have to be dealt using a policy mechanism or by just shielding the decision process from the user - like its done in elevators in a building (if one user wants to go up & another wants to go down, the elevator decides intelligently what it should do - it only takes input from the users as requests & does not treat them as commands).

Resource Discovery

• Three components: SIP (Service Interaction Proxy), SIC (Service Interaction Client) & Beaconing Daemons.
• SIC runs on client devices & provides the functionality for discovering services.
• SIP runs at domain specific granularities.
• Beaconing Daemons run at base-stations & advertise the availability of resources. The beacons may not carry the advertisements but may just have the address of a nearby SIP.
• In order that the objects cannot be controlled by malicious users from across the country, the beaconing daemons beacon a cookie (random number) along with the service advertisements. Thus only the clients having this cookie will be allowed access to the services. The problem of network security is hence reduced to that of physical security. (If a client can move into a building with a device turned on and hear the cookies, then he/she can have access to the resources).

Mapping Control

• The display may be device/client specific. Hence the interface provided should also be modifiable.
• An Interface Specification Language (ISL) is defined for specifying controls. The ISL combines the functionality of parameter passing conventions like CORBA IDL (Interface Definition Language) & the functionality of model-based user interface definitions.
• The ISL compiler (which compiles into a client specific UI) may be present in the mobile device or could be present in a proxy (maybe the SIP itself).