The Collaborative International Dictionary of English v.0.48:

Downstream \Down"stream`\, adv.
   Down the stream; as, floating downstream.
   [1913 Webster]

WordNet (r) 3.0 (2006):

downstream
    adv 1: away from the source or with the current [syn:
           downriver, downstream] [ant: upriver, upstream]
    adj 1: in the direction of a stream's current [ant: upstream]

The Free On-line Dictionary of Computing (30 December 2018):

upstream
downstream

    Fewer network hops away from a backbone or
   hub.  For example, a small ISP that connects to the
   Internet through a larger ISP that has their own connection
   to the backbone is downstream from the larger ISP, and the
   larger ISP is upstream from the smaller ISP.

   (1999-08-05)