What is the difference between HDLC and ppp?

HDLC

1.It is vendor specific.

2.It doesnt support authentication.

3.It supports synchronous network only.

4.It doesnt support multiplexing.

PPP

1.It is a standard protocol.

2.It supports authentication, like: PAP and CHAP.

3.It supports synchronous as well as asynchronous network.

4.But it supports multiplexing, like: multilinks.