PPP Background 101
Foundation Topics
PPP Background
RFC 1661 defines PPP. PPP's basic function is to encapsulate network layer protocol
information over point-to-point links. The mechanics of PPP are as follows:
Step 1
To establish communications, each end of the PPP link must first
send Link Control Protocol (LCP) packets to configure and test
the data link.
Step 2
After the link has been established and optional facilities have
been negotiated as needed, PPP must send Network Control
Protocol (NCP) packets to choose and configure one or more
network layer protocols.
Step 3
Once each of the chosen network layer protocols has been
configured, traffic from each network layer protocol can be sent
over the link.
Step 4
The link remains configured for communications until explicit
LCP or NCP packets close the link down, or until some external
event occurs (such as the expiration of an inactivity timer expires
or the intervention of a network administrator). In other words,
PPP is a pathway that is opened for multiple protocols
simultaneously.
PPP was originally developed with IP in mind; however, it functions independently of the
Layer 3 protocol that is traversing the link.
PPP Architecture
As mentioned, PPP encapsulates the network layer protocol(s) that are configured to traverse a PPP-
configured link. PPP has a number of capabilities that make it flexible and versatile, including:
·
Multiplexing of network layer protocols
·
Link configuration
·
Link quality testing
·
Authentication
·
Header compression
·
Error detection
·
Link parameter negotiation