  We consider a source that collects a multiplicity of streams of updates and
sends them through a network to a monitor. However, only a single update can be
in the system at a time. Therefore, the transmitter always preempts the packet
being served when a new update is generated. We consider Poisson arrivals for
each stream and a common general service time, and refer to this system as the
multi-stream M/G/1/1 queue with preemption. Using the detour flow graph method,
we compute a closed form expression for the average age and the average peak
age of each stream. Moreover, we deduce that although all streams are treated
equally from a transmission point of view (they all preempt each other), one
can still prioritize a stream from an age point of view by simply increasing
its generation rate. However, this will increase the sum of the ages which is
minimized when all streams have the same update rate.
