Authentication,
with PAP or CHAP, is used as a security measure with PPP
and PPP callback. Authentication allows the dialup target to
identify that any given dialup client is a valid client with a
preassigned username and password.
Callback is a
PPP option used to provide call and dialup billing consolidation.
PPP callback was first supported in Cisco IOS Release 11.0(3).
Compression
is used to improve throughput across existing lines. PPP
compression was first supported in Cisco IOS Release 10.3. As you
will see later, Cisco routers support Stacker, Predictor, and
Microsoft Point to Point Compression (MPPC).
Multilink PPP
(MLP) takes advantage of multiple bearer channels to improve
throughput. Datagrams are split, sequenced, transmitted across
multiple links, and then recombined at the destination. The
multiple links together are called a bundle. Multilink is
especially useful with ISDN, in which both B channels can be used
to achieve 128-Kbps throughput. MLP also works with modems to
provide additional bandwidth. This protocol was first supported in
Cisco IOS Release 11.0(3).