  We consider a multi-source status update system in which status updates are
transmitted as packets containing the measured value of the monitored process
and a time stamp representing the time when the sample was generated. The
packets of each source are generated according to the Poisson process and the
packets are served according to an exponentially distributed service time. We
assume that the received status update packets needs further processing before
being used (hence, computation-intensive). This is mathematically modeled by
introducing an additional server at the sink node. The sink server serves the
packets according to an exponentially distributed service time. We introduce
two packet management policies, namely, i) a preemptive policy and ii) a
blocking policy and derive the moment generating function (MGF) of the AoI of
each source under both policies. In the preemptive policy, a new arriving
packet preempts any possible packet that is currently under service regardless
of the packet's source index. In the blocking policy, when a server is busy at
the arrival instant of a packet the arriving packet is blocked and cleared. We
assume that the same preemptive/blocking policy is employed in both transmitter
and sink servers. Numerical results are provided to assess the results.
