  Progress in the development of techniques for the construction of multiuser
quantum communications networks is reviewed in light of the plans for an EU
quantum communications infrastructure (EU QCI). Quantum key distribution
networks may be classified as trusted node; quantum
repeater-entanglement-swapping based; point-to-multipoint based on passive beam
splitters, active optical switchers or WDM; high dimensional-multipartite
entanglement and flexible reconfigurable multipartite networks. Both satellite
and terrestrial implementations are possible and ore both planned for EU QCI;
their relative merits are discussed. Current technology falls short in several
respects of what is required to address use cases well. Bit rates as a function
of distance are currently limited by the characteristics of available devices
and are an order of magnitude or more below the theoretical bounds. Non-ideal
device behaviour can open loopholes for side-channel attacks. Limited range
constrains network geometry. New techniques are being developed to overcome
these problems. The more sophisticated schemes depend on ongoing advances in
the generation and distribution of entanglement. Particularly promising are the
measurement device independent protocol, which eliminates photon-detector
related security weaknesses, and the twin-field protocol, which uses similar
techniques to extend range, in principle even beyond previously accepted
theoretical bounds. Agreement of keys between more than two users can be
accomplished classically after pairwise quantum key exchange but direct quantum
multipartite agreement using may offer advantages. The same applies to secret
sharing. Practical quantum repeaters, to eliminate the need for trusted nodes,
are closer to being realised due to recent progress in optical memories.
