GSM air interface

Hi,

What is the interface between the BSC and GSM's core network - A, Gb?
Is this a radio interface?

And how about the internal interfaces inside the Core network block - H/E, Gr/Gs, Gn?
Are they radio interfaces as well?

And finally, how do the GSM's core network communicate with the external networks - PSTN, Internet?
Through wires?

Thank you.**broken link removed**