  In this paper, we study an age of information minimization problem in
continuous-time and discrete-time status updating systems that involve multiple
packet flows, multiple servers, and transmission errors. Four scheduling
policies are proposed. We develop a unifying sample-path approach and use it to
show that, when the packet generation and arrival times are synchronized across
the flows, the proposed policies are (near) optimal for minimizing any
time-dependent, symmetric, and non-decreasing penalty function of the ages of
the flows over time in a stochastic ordering sense.
