An evaluation of location-demographic replacement policies for zebroids

In an ad-hoc network of mobile devices, a device is termed a zebroid when it carries a data item residing on a server-device to a client-device referencing that item. The system employs a zebroid when its travel path intersects that of the server and the client and this information is known in advance. The motivation for use of a zebroid is to minimize the delay incurred by the client for the referenced data item, termed the availability latency. This paper considers the performance of alternative policies that manage the identity of data items assigned to a zebroid when its storage is exhausted. One novel policy is LoDeR that manages storage of zebroids based on the demographics of a geographical region where the zebroid rendezvous with the client. Experimental results demonstrate a host of tradeoffs between the different performance metrics such as the number of data items lost by a policy and the percentage of requests that reference these data items, availability latency, and number of replaced data items. The mobility model has a significant impact on these metrics for a given policy.