PPP can be configured to support various optional functions, as shown in Figure 1. These optional functions include:
- Authentication using either PAP or CHAP
- Compression using either Stacker or Predictor
- Multilink that combines two or more channels to increase the WAN bandwidth
To negotiate the use of these PPP options, the LCP link-establishment frames contain option information in the data field of the LCP frame, as shown in Figure 2. If a configuration option is not included in an LCP frame, the default value for that configuration option is assumed.
This phase is complete when a configuration acknowledgment frame has been sent and received.