upstream / downstream
expressionISP & telecom
The two directions of an access link: downstream toward the subscriber, upstream toward the internet - historically sized very unequally.
Video calls and cloud backups made the skinny upstream everyone's problem.
Upstream and downstream describe direction relative to you, and the words are used in at least three unrelated ways that regularly collide in the same conversation. In access networks, downstream is toward the subscriber and upstream is toward the provider, which is why residential connections are asymmetric.
In routing and business relationships, an upstream is the provider you buy transit from and a downstream is the customer who buys from you, which encodes money rather than direction. In software supply chains, upstream is the project you take code from and downstream is whoever takes yours, so a patch sent upstream travels toward the origin, and an upstream security fix flows down to everyone else.
The collisions are real and worth catching. A conversation about an upstream problem may mean the provider, the origin project, or the direction of traffic, and the three have different owners and different fixes. The habit that avoids it is naming the thing rather than the direction, since the extra three words cost nothing and the ambiguity costs a misdirected escalation.