What is a PPP server, and why do I keep getting disconnected from it?
PPP is the Point to Point Protocol is a data link layer (see the OSI 7-layer model). It's an older protocol that's generally used to connect two points together over a physical link like a phone line. It's been in use as a connection protocol (mostly in the PPPoE -- PPP over Ethernet -- form) for ISPs for quite some time now. Your modem uses this protocol to identify you as a customer to your ISP and create a tunnel to them over some larger network, through which your data will flow. Your modem establishes a PPP connection and then over this connection your Ethernet packets flow.

It sounds like you're disconnecting from your ISP at regular intervals. It could be any number of things causing you to lose your connection. You may have poor signal to the ISP end point and the connection is timing out. You may be overloading the connection and your ISP is dropping the link. Your ISP may be having issues. You may have failing or buggy hardware. Or you may have buggy drivers for your hardware.

It's impossible to tell exactly from what you've written.

If you can check your Console logs, see if there are related console messages about the PPP tunnel, you might be able to find something additionally useful to add to your question.

Have you called your ISP? That's where I'd start.