Point-to-Point Protocol
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OmniAccess 5740 Unified Services Gateway CLI Configuration Guide
Alcatel-Lucent
PPP OVERVIEW
The PPP protocol emerged as an encapsulation protocol for transporting IP traffic
over point-to-point links. PPP also established a standard for the assignment and
management of IP addresses, network protocol multiplexing, link configuration,
link quality testing, error detection and option negotiation for such capabilities as
network layer address and data compression. PPP supports these functions by
providing an extensible LCP and a family of NCPs to negotiate optional
configuration parameters and facilities. PPP supports IP through IPCP.
PPP and its associated protocols are specified in the following IETF documents:
• PPP (RFC 1661)
• PPP in HDLC-like framing (RFC 1662)
• IPCP (RFC 1332)
• PAP (RFC 1334)
• CHAP (RFC 1994)
• EAP (RFC 3748)
The Alcatel-Lucent implementation of PPP conforms to the above specifications.
PPP COMPONENTS
PPP provides a method for transmitting datagrams over point-to-point links. On a
serial interface, PPP contains four main components:
• HDLC-like Framing - PPP uses framing similar to HDLC as a basis for
encapsulating datagrams over serial links. (For more information, see “High-level
Data Link Control” chapter.)
• LCP - PPP uses an extensible LCP to establish, configure, and test data link
connection.
• Authentication - Authentication protocols PAP, CHAP, EAP are used to
authenticate the peer.
• NCP - PPP uses a family of NCPs for establishing and configuring different
network layer protocols.
PPP OPERATION
To establish communication over a PPP link, the originating PPP peer first sends
LCP messages to configure the data link. After the link has been established and
optional facilities have been negotiated as needed by LCP, each PPP end-point
may authenticate its peer. Then NCP messages are sent to choose and configure
one or more network layer protocols.
When each of the chosen network layer protocols has been configured, packets
from each network layer protocol can be sent over the link. The link remains
configured for communication until an explicit LCP or NCP message terminates
the connection, or until events like user intervention or an expiry of a keep alive
timer occur.
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