Sterling File Gateway vs sterling VAN/WAN

Hi

I am working on SAP PO B2B add-on and need to post/pick EDI files.

Customer says I need to pick files from Sterling File Gateway/Sterling VAN.

Sometimes customer uses the name Sterling File Gateway and some times they use the name Sterling VAN.

Are they both the same and people use loosely both the names ??

Anybody knows the difference between these ?

Thanks

Kumar