  A source node updates its status as a point process and also forwards its
updates to a network of observer nodes. Within the network of observers, these
updates are forwarded as point processes from node to node. Each node wishes
its knowledge of the source to be as timely as possible. In this network,
timeliness is measured by a discrete form of age of information: each status
change at the source is referred to as a version and the age at a node is how
many versions out of date is its most recent update from the source. This work
introduces a method for evaluating the average version age at each node in the
network when nodes forward updates using a memoryless gossip protocol. This
method is then demonstrated by version age analysis for a collection of simple
networks. For gossip on a complete graph with symmetric updating rates, it is
shown that each node has average age that grows as the logarithm of the network
size.
