Pushing dependent data in clients-providers-servers systems

In a satellite and wireless networks and in advanced traffic information systems in which the up-link bandwidth is very limited, a server broadcasts data files in a round-robin manner. The data files are provided by different providers and are accessed by many clients. The providers are independent and therefore files may share information. The clients who access these files may have different patterns of access. Some clients may wish to access more than one file at a time in any order, some clients may access one file out of of several files, and some clients may wish to access a second file only after accessing another file. The goal of the server is to order the files in a way that minimizes the access time of the clients given some a-priori knowledge of their access patterns. This paper introduces a clients-providers-servers model that represents certain environments better than the traditional clients-servers model. Then, we show that a random order of the data files performs well independent of the specific access pattern. Our main technical contribution is showing how to de-randomize the randomized algorithm that is based on selecting a random order. The resulting algorithm is a polynomial time deterministic algorithm that finds an order that achieves the bounds of the random order.