The Link Control Protocol (LCP) establishes the connection through an exchange of configure packets. This exchange is complete, and the LCP opened state entered, after a Configure-Ack packet has been both sent and received.
LCP allows for the negotiation of multiple options in a PPP session. MLPPP is somewhat different than PPP and therefore the following options are set for MLPPP and not negotiated:
No async control character map
No link quality monitoring
No compound frames
No self-describing-padding
Any non-LCP packets received during this phase must be silently discarded.