  As the research community starts to address the* key features of 6G cellular
standards, one of the agreed bridge topics to be studied already in 5G advanced
releases is Integrated Sensing and Communication (ISAC). The first efforts of
the research community are focusing on ISAC enablers, fundamental limits, and
first demonstrators, that show that the time has come for the deployment of
sensing functionalities in cellular standards. This survey paper takes a needed
step towards ISAC deployment, providing an analytical toolkit to model cellular
systems' sensing performance, accounting for both their fundamental and
practical constraints. We then elaborate on the likely features of 6G systems
to provide the feasible sensing key performance indicators (KPIs) in the
frequency ranges spanned by cellular networks, including the potential new
bands available in 6G, the Frequency Range 3 (FR3). We further validate our
framework by visually investigating ISAC constraints with simulation examples.
Finally, we assess the feasibility of few selected scenarios that can be
enabled by ISAC, highlighting in each of them the limiting factor and, thus,
which gaps should be filled by the research and standardization communities in
the next years.
