  Freshness of data is an important performance metric for real-time
applications, which can be measured by age-of-information. For
computation-intensive messages, the embedded information is not available until
being computed. In this paper, we study the age-of-information for
computation-intensive messages, which are firstly transmitted to a mobile edge
server, and then processed in the edge server to extract the embedded
information. The packet generation follows zero-wait policy, by which a new
packet is generated when the last one is just delivered to the edge server. The
queue in front of the edge server adopts one-packet-buffer replacement policy,
meaning that only the latest received packet is preserved. We derive the
expression of average age-of-information for exponentially distributed
transmission time and computing time. With packet replacement, the average age
is reduced compared with the case without packet replacement, especially when
the transmission rate is close to or greater than the computing rate.
