  We review recent results on the simulation of quantum channels, the reduction
of adaptive protocols (teleportation stretching), and the derivation of
converse bounds for quantum and private communication, as established in PLOB
[Pirandola, Laurenza, Ottaviani, Banchi, arXiv:1510.08863]. We start by
introducing a general weak converse bound for private communication based on
the relative entropy of entanglement. We discuss how combining this bound with
channel simulation and teleportation stretching, PLOB established the two-way
quantum and private capacities of several fundamental channels, including the
bosonic lossy channel. We then provide a rigorous proof of the strong converse
property of these bounds by adopting a correct use of the Braunstein-Kimble
teleportation protocol for the simulation of bosonic Gaussian channels. This
analysis provides a full justification of claims presented in the follow-up
paper WTB [Wilde, Tomamichel, Berta, arXiv:1602.08898] whose upper bounds for
Gaussian channels would be otherwise infinitely large. Besides clarifying
contributions in the area of channel simulation and protocol reduction, we also
present some generalizations of the tools to other entanglement measures and
novel results on the maximum excess noise which is tolerable in quantum key
distribution.
