  Suitable composable data center networks (DCNs) are essential to support the
disaggregation of compute components in highly efficient next generation data
centers (DCs). However, designing such composable DCNs can be challenging. A
composable DCN that adopts a full mesh backplane between disaggregated compute
components within a rack and employs dedicated interfaces on each
point-to-point link is wasteful and expensive. In this paper, we propose and
describe two (i.e., electrical, and electrical-optical) variants of a network
for composable DC (NetCoD). NetCoD adopts a targeted design to reduce the
number of transceivers required when a mesh physical backplane is deployed
between disaggregated compute components in the same rack. The targeted design
leverages optical communication techniques and components to achieve this with
minimal or no network performance degradation. We formulate a MILP model to
evaluate the performance of both variants of NetCoD in rack-scale composable
DCs that implement different forms of disaggregation. The electrical-optical
variant of NetCoD achieves similar performance as a reference network while
utilizing fewer transceivers per compute node. The targeted adoption of optical
technologies by both variants of NetCoD achieves greater (4 - 5 times greater)
utilization of available network throughput than the reference network which
implements a generic design. Under the various forms of disaggregation
considered, both variant of NetCoD achieve near-optimal compute energy
efficiency in the composable DC while satisfying both compute and network
constraints. This is because marginal concession of optimal compute energy
efficiency is often required to achieve overall optimal energy efficiency in
composable DCs.
