|  | 4.2 | PPP Session Establishment
| 4.2.3 | Phase 2: link-quality determination
LCP allows an optional link-quality determination phase following the link establishment and configuration negotiation phase. In the link-quality determination phase, the link is tested to determine whether the link quality is good enough to bring up network-layer protocols. In addition, after the link has been established and the authentication protocol chosen, the client or user workstation can be authenticated. Authentication, if used, takes place before the network-layer protocol configuration phase begins. LCP can delay transmission of network-layer protocol information until this phase is completed. PPP supports two authentication protocols: Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP). Both of these protocols are detailed in RFC 1334, "PPP Authentication Protocols." These protocols are covered later in this chapter, in the section "PPP Authentication."