Minimum cost mirror sites using network coding: Replication vs. coding at the source nodes

TL;DR

This paper investigates the optimal placement of mirror sites using network coding versus replication in content distribution networks, formulating cost-minimization problems and providing bounds and algorithms for source content placement.

Contribution

It introduces a cost-based optimization framework for network coding and replication in mirror sites, deriving bounds and algorithms for source content placement.

Findings

No loss in considering subset sources with two nodes.

Derived tight upper bounds on cost gaps for three nodes.

Presented algorithms for source content determination.

Abstract

Content distribution over networks is often achieved by using mirror sites that hold copies of files or portions thereof to avoid congestion and delay issues arising from excessive demands to a single location. Accordingly, there are distributed storage solutions that divide the file into pieces and place copies of the pieces (replication) or coded versions of the pieces (coding) at multiple source nodes. We consider a network which uses network coding for multicasting the file. There is a set of source nodes that contains either subsets or coded versions of the pieces of the file. The cost of a given storage solution is defined as the sum of the storage cost and the cost of the flows required to support the multicast. Our interest is in finding the storage capacities and flows at minimum combined cost. We formulate the corresponding optimization problems by using the theory of information measures. In particular, we show that when there are two source nodes, there is no loss in considering subset sources. For three source nodes, we derive a tight upper bound on the cost gap between the coded and uncoded cases. We also present algorithms for determining the content of the source nodes.