  For millimeter-wave (mm-wave) buffer-aided tandem networks consisting of
relay nodes and multiple channels per hop, we consider two traffic allocation
schemes, namely local allocation and global allocation, and investigate the
end-to-end latency of a file transfer. We formulate the problem for generic
multi-hop queuing systems and subsequently derive closed-form expressions of
the end-to-end latency. We quantify the advantages of the global allocation
scheme relative to its local allocation counterpart, and we conduct an
asymptotic analysis on the performance gain when the number of channels in each
hop increases to infinity. The traffic allocations and the analytical delay
performance are validated through simulations. Furthermore, taking a specific
two-hop mm-wave network as an example, we derive lower bounds on the average
end-to-end latency, where Nakagami-$m$ fading is considered. Numerical results
demonstrate that, compared to the local allocation scheme, the advantage of
global allocation grows as the number of relay nodes increases, at the expense
of higher complexity that linearly increases with the number of relay nodes. It
is also demonstrated that a proper deployment of relay nodes in a linear
mm-wave network plays an important role in reducing the average end-to-end
latency, and the average latency decays as the mm-wave channels become more
deterministic. These findings provide insights for designing multi-hop mm-wave
networks with low end-to-end latency.
