Definition
A public, shared communications network that carries digital data between users by switching it through routing equipment, much like the public telephone system switches voice calls between callers. In aviation, a PSDN is one of the underlying networks that can carry flight-related data messages between ground systems and, in some cases, between ground and aircraft.
Plain English
A shared data network — open to many users — that moves digital information from one point to another by routing it through the network, similar to how the phone system connects calls.
Context Anchor
Seen in FAA acronym lists and in references to aviation communication or data-link systems that use outside data networks.
Derivation
Public means open to many users rather than private. Switched means the network routes each message through whichever path is available at the moment, instead of using a single dedicated line. Data network means it carries digital information rather than voice. Together: a shared, routed network for digital data.
Why Pilots Care
Pilots rarely deal with a PSDN directly, but it is part of the plumbing behind datalink weather, clearances, and flight information services. Knowing the term helps when reading about how aviation data actually gets from one place to another.
Analogy
It is like using the regular telephone system for data: many users share the same larger system, and the network connects each call or data session where it needs to go.
Intuition Check
Public does not mean the data is simply open for anyone to read; here it means the network is a shared service rather than a private one. Switched does not mean a cockpit switch; it means the network routes the data connection through its own equipment.
Example Sentence 1
The ground service provider delivered weather updates over a PSDN before forwarding them to the aircraft via datalink.
Example Sentence 2
Older flight planning tools connected through the PSDN to retrieve updated weather products.