Any kind of application that acts as a server needs a direct IP connection.
Gamers get errors about "strict NAT." Traditionally the solution to this problem caused by NAT was to forward the ports. If their ISPs has chosen CGNAT port forwarding is impossible.
VoIP calls that have one way audio are a symptom of reachability issues caused by a firewall or address translation problems. VoIP services have adapted to IPv4 NAT by relying on proxying instead of STUN but CGNAT really degrades reliability.
Video chat uses the kludges of TURN when peer to peer connectivity does not work. This increases costs for the video chat service who in turn require a paid subscription as they will not relay traffic for free.
BitTorrent and file transfer services need direct IP connectivity. If p2p file transfers worked on any network we would not need to mind Gmail's 25MB attachment limit, or pay for intermediary cloud storage.
Gamers get errors about "strict NAT." Traditionally the solution to this problem caused by NAT was to forward the ports. If their ISPs has chosen CGNAT port forwarding is impossible.
VoIP calls that have one way audio are a symptom of reachability issues caused by a firewall or address translation problems. VoIP services have adapted to IPv4 NAT by relying on proxying instead of STUN but CGNAT really degrades reliability.
Smaller newer ISPs that can't obtain one IPv4 address per household are incurring signicant CGNAT costs. https://news.ycombinator.com/item?id=35047624
Video chat uses the kludges of TURN when peer to peer connectivity does not work. This increases costs for the video chat service who in turn require a paid subscription as they will not relay traffic for free.
BitTorrent and file transfer services need direct IP connectivity. If p2p file transfers worked on any network we would not need to mind Gmail's 25MB attachment limit, or pay for intermediary cloud storage.