Connectivity and Synchronization Requirements
Connectivity between client and navigation service provider has three dimensions:
- Availability. Availability measures how much of the time a connection is actually available. Availability can be quantified by the average, minimum, and maximum wait times between the initiation of a connection by an application and the minimum, average, and maximum time before unexpected loss of connection. High availability implies low wait time and long connection time.
- Bandwidth. Bandwidth is the net bit rate of useful messages between client and server during a connection. Mobile devices operating over wireless connections may be forced to operate with effective bandwidths under 9.6 KBps!
- Latency. Latency measures the delay between a client request and a server response. Latency may involve more than simple network characteristics if the server s time to serve the request is significant. Latency is an issue especially in synchronous, stateless operations where client, server, and the mobile user s motion through the real world must be in harmony for an application to be useful and safe.
In comparison with other networks, mobile delivery has poor availability, low bandwidth, and unpredictable latency. Since many applications require better performance, these characteristics should improve over time. If we look at today s situation however, the uncertainties of availability and latency encourage a strategy of caching and synchronization. The main driving factor in determining how extensively they must be pursued is the timing requirements of the application itself. Pedestrian navigation support or panic button services cannot benefit much from caching. In-car navigation systems on the other hand cannot function without autonomous real-time capabilities, based on cached local information and periodic updates.