HP ProCurve 7000dl Series Basic Management And Configuration Manual page 301

Configuring the Data Link Layer Protocol for E1, T1, and Serial Interfaces
Exchanging an authentication protocol is optional.
Understanding how a PPP session is established can help you troubleshoot
problems if they occur. (See Figure 6-3.)
ProCurve
Secure Router
Figure 6-3. Establishing a PPP Link
Link Establishment. Two PPP peers exchange LCP frames to establish,
configure, and test the WAN link. These frames allow the peers to determine
if the link can accommodate the data they want to transfer. The LCP frames
also contain a field called the configuration option. Configuration options
inform the peer desired settings for the link such as the size of the PPP
datagrams that will be sent and their degree of compression.
The two peers negotiate these settings. If the LCP frames do not contain a
particular configuration option field, the peers use the default configuration
for that option.
Authentication Protocol. If authentication is configured, the two peers
authenticate the link. Although authentication is optional, the peers pass
through this phase whether or not authentication is chosen.
PPP supports several authentication protocols:
Password Authentication Protocol (PAP)
Challenge Handshake Authentication Protocol (CHAP)
Extensible Authentication Protocol (EAP)
The ProCurve Secure Router supports PAP and CHAP.
1. Link establishment
LCP
2. Authentication (optional)
PAP, CHAP, or EAP
3. Negotiation of Network Layer protocols
NCP: IPCP, BCP, and so on
4. Session established
PPP
Configuring the Logical Interface
ProCurve
Secure Router
6-5