nstream is a wireless protocol mikrotik proprietary.
it allows fast data exchange and more robust channels, either in point-to-point and in point-to-multipoint.
this protocol have a lot of advanteges.
but it can be used only between mikrotik routers (i.e. from a mikrotik and an ubnt device, you cant use nstream).
now mikrotik try to replace it with NV2, with with mixed success.