  This is a three part paper.
  Optimality of source-channel separation for communication with a fidelity
criterion when the channel is compound as defined by Csiszar and Korner in
their book and general as defined by Verdu and Han, is proved in Part I. It is
assumed that random codes are permitted. The word "universal" in the title of
this paper refers to the fact that the channel model is compound. The proof
uses a layered black-box or a layered input-output view-point. In particular,
only the end-to-end description of the channel as being capable of
communicating a source to within a certain distortion level is used when
proving separation. This implies that the channel model does not play any role
for separation to hold as long as there is a source model. Further implications
of the layered black-box view-point are discussed.
  Optimality of source-medium separation for multi-user communication with
fidelity criteria over a general, compound medium in the unicast setting is
proved in Part II, thus generalizing Part I to the unicast, multi-user setting.
  Part III gets to an understanding of the question, "Why is a channel which is
capable of communicating a source to within a certain distortion level, also
capable of communicating bits at any rate less than the infimum of the rates
needed to code the source to within the distortion level": this lies at the
heart of why optimality of separation for communication with a fidelity
criterion holds. The perspective taken to get to this understanding is a
randomized covering-packing perspective, and the proof is operational.
