A file storage scheme is proposed for networks containing heterogeneous clients. In the scheme, the performance measured by file-retrieval delays degrades gracefully under increasingly serious faulty circumstances. The scheme combines coding with storage for better performance. The problem is NP-hard for general networks; and this paper focuses on tree networks with asymmetric edges between adjacent nodes. A polynomial-time memory-allocation algorithm is presented, which determines how much data to store on each node, with the objective of minimizing the total amount of data stored in the network. Then a polynomial-time data-interleaving algorithm is used to determine which data to store on each node for satisfying the quality-of-service requirements in the scheme. By combining the memory-allocation algorithm with the data-interleaving algorithm, an optimal solution to realize the file storage scheme in tree networks is established.

Abstract — Interleaving codewords is an important method not only for combatting burst-errors, but also for distributed data retrieval. This paper introduces the concept of Multi-Cluster Interleaving (MCI), a generalization of traditional interleaving problems. MCI problems for paths and cycles are studied. The following problem is solved: how to interleave integers on a path or cycle such that any m (m ≥ 2) non-overlapping clusters of order 2 in the path or cycle have at least 3 distinct integers. We then present a scheme using a ‘hierarchical-chain structure’ to solve the following more general problem for paths: how to interleave integers on a path such that any m (m ≥ 2) nonoverlapping clusters of order L (L ≥ 2) in the path have at least L + 1 distinct integers. It is shown that the scheme solves the second interleaving problem for paths that are asymptotically as long as the longest path on which an MCI exists, and clearly, for shorter paths as well.