The PPP Daemon is the userland part of the Point-to-Point Protocol. It works
in combination with a dedicated kernel network interface usually named ppp.
PPP is a very extensible protocol and pppd supports a large number of options,
including compression (through various algorithms), cryptography (Microsoft's
MPPE) and authentication (PAP, CHAP, Microsoft CHAP), provided the kernel has
the relevant back-ends in some cases.
