  In this paper, we consider N information streams sharing a common service
facility. The streams are supposed to have different priorities based on their
sensitivity. A higher priority stream will always preempt the service of a
lower priority packet. By leveraging the notion of Stochastic Hybrid Systems
(SHS), we investigate the Age of Information (AoI) in the case where each
stream has its own waiting room; when preempted by a higher priority stream,
the packet is stored in the waiting room for future resume. Interestingly, it
will be shown that a "no waiting room" scenario, and consequently discarding
preempted packets, is better in terms of average AoI in some cases. The exact
cases where this happen are discussed and numerical results that corroborate
the theoretical findings and highlight this trade-off are provided.
