Characteristics of Mobile Environments

Some of the characteristics of computing in the mobile environment include

·   High communication latency

·   Intermittent wireless connectivity

·   Limited battery life

·   Changing client location.

·         Latency is caused by the processes unique to the wireless medium, such as coding data for wireless transfer, and tracking and filtering wireless signals at the receiver.

·         Battery life is directly related to battery size, and indirectly related to the mobile device’s capabilities.

·         Intermittent connectivity (Types)

                                i.      Intentional

             Intentional disconnections occur by user intent, e.g., during the takeoff of an airplane, or when the mobile device is powered down.

                              ii.      Unintentional.

Unintentional disconnections happen in areas wireless signals cannot reach, e.g., elevator shafts or subway tunnels.

·         To compensate for high latencies and unreliable connectivity, clients cache replicas of important, frequently accessed data, and work offline, if necessary.

·         Besides increasing data availability and response time, caching can also reduce client power consumption by eliminating the need to make energy-consuming wireless data transmissions for each data access.

·         On the other hand, the server may not be able to reach a client. A client may be unreachable because it is dozing—in an energy-conserving state in which many subsystems are shut down—or because it is out of range of a base station.

·         In either case, neither client nor server can reach the other, and modifications must be made to the architecture in order to compensate for this case.

·         Proxies for unreachable components are added to the architecture. For a client (and symmetrically for a server), the proxy can cache updates intended for the server. When a connection becomes available, the proxy automatically forwards these cached updates to their ultimate destination.

·         Mobile computing poses challenges for servers as well as clients. The latency involved in wireless communication makes scalability a problem. Because latency due to wireless communications increases the time to service each client request, the server can handle fewer clients. One way servers relieve this problem is by broadcasting data whenever possible.