  This paper is motivated by emerging edge computing applications in which
generated data are pre-processed at the source and then transmitted to an edge
server. In such a scenario, there is typically a tradeoff between the amount of
pre-processing and the amount of data to be transmitted. We model such a system
by considering two non-preemptive queues in tandem whose service times are
independent over time but the transmission service time is dependent on the
computation service time in mean value. The first queue is in M/GI/1/1 form
with a single server, memoryless exponential arrivals, general independent
service and no extra buffer to save incoming status update packets. The second
queue is in GI/M/1/2* form with a single server receiving packets from the
first queue, memoryless service and a single data buffer to save incoming
packets. Additionally, mean service times of the first and second queues are
dependent through a deterministic monotonic function. We perform stationary
distribution analysis in this system and obtain closed form expressions for
average age of information (AoI) and average peak AoI. Our numerical results
illustrate the analytical findings and highlight the tradeoff between average
AoI and average peak AoI generated by the tandem nature of the queueing system
with dependent service times.
