  We consider a multi-source relaying system where the sources independently
and randomly generate status update packets which are sent to the destination
with the aid of a bufferaided relay through unreliable links. We formulate a
stochastic optimization problem aiming to minimize the sum average age of
information (AAoI) of sources under per-slot transmission capacity constraints
and a long-run average resource constraint. To solve the problem, we recast it
as a constrained Markov decision process (CMDP) problem and adopt the
Lagrangian method. We analyze the structure of an optimal policy for the
resulting MDP problem that possesses a switching-type structure. We propose an
algorithm that obtains a stationary deterministic near-optimal policy,
establishing a benchmark for the system. Simulation results show the
effectiveness of our algorithm compared to benchmark algorithms.
