Link Control Protocol

In computer networking, the Link Control Protocol forms part of the Point-to-Point Protocol, within the family of Internet protocols. In setting up PPP communications, both the sending and receiving devices send out LCP packets to determine the standards of the ensuing data transmission.
The protocol:

checks the identity of the linked device and either accepts or rejects the device
determines the acceptable packet size for transmission
searches for errors in configuration
can terminate the link if requirements exceed the parameters

LCP packets are sent during the Link Establishment Phase of PPP, after the physical layer has been made ready from the Link Dead state. No transmission of network-layer protocols such as IP may be transmitted across PPP until after the Link Establishment or Authentication phases are complete. When a connection is requested by a peer to be terminated, the Link Termination Phase is performed, and PPP returns to the Link Dead state.