<p>In this paper, we concentrate on the peak age of information (PAoI)
in a discrete-time slotted ALOHA network comprised of <i>M</i> buffer-less
nodes, capable of keeping just one packet at each time. In this network,
whenever some nodes transmit their packets simultaneously, a collision happens,
thus there is interaction among queues and transmission delay of a packet might
prolong more than one slot. The packets are generated at each node
stochastically and independently. The nodes follow preemptive queueing policy.
In this network, we propose a new trellis-based analytical model to represent
the interaction among queues and derive exact average PAoI in closed form.
Furthermore, we find average PAoI-constrained regions and minimize average PAoI
for a symmetric network, numerically. As a byproduct of our analysis, the achievable
throughput region of two slotted ALOHA networks with unlimited buffer and
buffer-less nodes are compared. We observe that the latter is superior not only
in AoI, but also in achievable throughput region. Simulation results confirm
our analysis.</p>
Peak age of information in slotted ALOHA network