Point-to-Point Agreement (PPP)
Let’s absorb a little time on PPP. Bethink that it’s a Data Articulation band agreement that can be used
over either asynchronous consecutive (dial-up) or ancillary consecutive (ISDN) media. It uses Link
Control Agreement (LCP) to body and advance data-link connections. Network Control Protocol
(NCP) is acclimated to acquiesce assorted Network band protocols (routed protocols) to be used
on a point-to-point connection.
Since HDLC is the absence consecutive encapsulation on Cisco consecutive links and it works great, why
and back would you accept to use PPP? Well, the basal purpose of PPP is to carriage layer-
3 packets beyond a Data Articulation band point-to-point link, and it’s nonproprietary. So unless you
have all Cisco routers, you charge PPP on your consecutive interfaces—the HDLC encapsulation is
Cisco proprietary, remember? Plus, back PPP can abbreviate several layer-3 baffled protocols
and accommodate authentication, activating addressing, and callback, PPP could be the best encapsulation
solution for you instead of HDLC.
Figure 11.2 shows the agreement assemblage compared to the OSI advertence model.
PPP contains four capital components:
EIA/TIA-232-C, V.24, V.35, and ISDN
A Physical band all-embracing accepted for serial
communication.
HDLC
A adjustment for encapsulating datagrams over consecutive links.