  We consider a communication system where a group of users, interconnected in
a bidirectional gossip network, wishes to follow a time-varying source, e.g.,
updates on an event, in real-time. The users wish to maintain their expected
version ages below a threshold, and can either rely on gossip from their
neighbors or directly subscribe to a server publishing about the event, if the
former option does not meet the timeliness requirements. The server wishes to
maximize its profit by increasing subscriptions from users and minimizing event
sampling frequency to reduce costs. This leads to a Stackelberg game between
the server and the users where the sender is the leader deciding its sampling
frequency and the users are the followers deciding their subscription
strategies. We investigate equilibrium strategies for low-connectivity and
high-connectivity topologies.
