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Considering middle-term predictions of the need for commercial 10-Tb/s optical interfaces working in 1-P b/s optical transport systems by 2024 and recalling the introduction of the optical bypass when entering the wavelength-abundant era in the early 2000s, we re-evaluate the values of hierarchical optical network architecture in light of the forthcoming massive spatial division multiplexing (SDM) era. We introduce a spatial channel (SCh) network (SCN) architecture, where the SDM layer is explicitly defined as a new networking layer that supports the new multiplexing technology of SDM. In an SCN, optical channels (OChs) accommodated in an express SCh bypass the overlying wavelength cross-connects (WXCs) using spatial cross-connects (SXCs) on the route. As one challenge that SCNs will present, we point out that an excessively large SXC insertion loss reduces the optical reach for spectrally groomed …