R in a Circle (Airport Surveillance Radar) on VFR charts

The R in a circle symbol indicates ASR is on the field, it's used
at airports when no other indication of the presence of radar exists, such
as Class B or C airspace or a TRSA.


Which raises another question. What is in a TRSA that isn't anywhere else? I
know a TRSA is sort of a stillborn class C, and (from the name) you can get
"radar services".

So, which ones?

Is it the case that you can get the same (radar) services in a TRSA that you
can get in class B or C airspace, or the airports with the circle R (that isn't
the one meaning "restricted/private airport"), and it's just that because of
traffic volume or the thought it would become a class C that the airspace was
carved into sectors?

And what services can you not get outside the sectors that you can get inside
them?

Jose

--
(for Email, make the obvious changes in my address)