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Three-Dimensional Integration of Network-on-Chip
the number of TSVs is large, which may cause floorplanning problems. To
reduce the number of interlayer vias, usage of a combination of 2D and
3D mesh-based network routers was proposed by Pavlidis and Friedman
(2009). Depending on the position of vertical interconnection links, a number of mesh-based heterogeneous 3D NoC structures were developed. The
performance, area requirement, and energy consumption of these heterogeneous networks were evaluated and compared with those of the fully
connected 3D mesh-based NoC.
Most of the research works in 3D NoC are based on mesh topology. There
are very few works reported on tree topologies. In any tree-based network,
the length of the interconnection link increases toward the root of the tree,
whereas the mesh structure has a uniform wire length. In a torus network,
the length of the end-around connection increases with increasing network
size. Therefore, torus and tree-based topologies may not be a good choice
for NoC designers while attempting large number of cores in a 2D IC. In 3D
IC implementation, due to the shorter TSVs, the intrinsic problem of having long interconnection wires in tree-based topologies gets significantly
resolved. Matsutani et al. (2008) instantiated a number of existing tree-based
topologies in 3D platform and showed the benefit of energy reduction
over their 2D implementation. Similar to Matsutani et al. (2008), instead
of proposing any new 3D tree-based topology, Feero and Pande (2009)
also instantiated the already existing butterfly fat tree (BFT) and the fat
tree structures in 3D platform to show the energy reduction over their
2D implementations. However, mesh-of-tree (MoT) topology in 3D context is not included in any of the existing studies. This chapter proposes
an extension of MoT topology for the 3D environment and carries out
performance and cost benefits of the proposed 3D structure over its 2D
counterpart. Detailed performance evaluation, energy consumption, and
area estimation have been carried out for the proposed structure and
compared with BFT and two variants of mesh networks for equal number
of cores in 3D NoC context. The salient contributions of this chapter are
as follows:
1. A new 3D MoT topology has been proposed. Expressions for the
number of directed edges and the average distance in an M × N × Z
MoT have been formulated.
2. Performance and cost of proposed MoT-based 3D NoC have been
evaluated under self-similar traffic. The results have been compared
with BFT and two variants of mesh networks, having the same number of cores, in 3D NoC context. Simulation results show MoT’s applicability as communication infrastructure design of 3D NoC.
3. Performance and cost benefits of all 3D NoC structures have been
shown over their 2D counterparts.