On the Multiple-Unicast Capacity of 3-Source, 3-Terminal Directed Acyclic Networks

  • Authors:
  • Shurui Huang;Aditya Ramamoorthy

  • Affiliations:
  • Dept. of Electrical & Computer Eng., Iowa State University, Ames, IA, USA;Dept. of Electrical & Computer Eng., Iowa State University, Ames, IA, USA

  • Venue:
  • IEEE/ACM Transactions on Networking (TON)
  • Year:
  • 2014

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Abstract

We consider the multiple-unicast problem with three source–terminal pairs over directed acyclic networks with unit-capacity edges. The three $s_i{\hbox{–}}t_i$ pairs wish to communicate at unit-rate via network coding. The connectivity between the $s_i{\hbox{–}}t_i$ pairs is quantified by means of a connectivity-level vector, $[k_1\ k_2\ k_3]$ such that there exist $k_i$ edge-disjoint paths between $s_i$ and $t_i$. In this paper, we attempt to classify networks based on the connectivity level. It can be observed that unit-rate transmission can be supported by routing if $k_i \geq 3$, for all $i = 1, \ldots, 3$. In this paper, we consider connectivity-level vectors such that $\min_{i = 1, \ldots, 3} k_i . We present either a constructive linear network coding scheme or an instance of a network that cannot support the desired unit-rate requirement, for all such connectivity-level vectors except the vector [1 2 4] (and its permutations). The benefits of our schemes extend to networks with higher and potentially different edge capacities. Specifically, our experimental results indicate that for networks where the different source–terminal paths have a significant overlap, our constructive unit-rate schemes can be packed along with routing to provide higher throughput as compared to a pure routing approach.