Can You Explain LCP Link Termination Packets , Link Monitoring And Debugging Packets?

LCP or Link Control Protocol is the protocol of point to point protocol stack. The link termination packets of LCP are used to terminate or disconnect the link between two end points. It contains the two types of packets that are terminate- request and terminate-ack packets. Either party can terminate the link by sending the terminate-request packet. The party that receives the terminate-request packet must answer with the terminate-ack packet.

The link monitoring and debugging packets are used for monitoring and debugging the link. It contains the code-reject, protocol-reject, echo-request, echo-reply and discard-request packets.  If the end point receives a packet with an unrecognised code in packet, it sends the code-reject packet. If the end point receives the packet with an unrecognised protocol in the frame, it sends a protocol-reject packet. The echo-request packet is sent to monitor the link. Its purpose is to see if the link is functioning properly. The sender expects to receive an echo-reply packet from other side as proof. The information in the echo-request packet is exactly duplicated and sent back to sender of the echo-request packet. The discard-request is a kind of loop back test packet. It is used by the sender to check all of its internal condition. The receiver of this packet just discards it.

One of the classes of LCP packet is the LCP termination packets and these packets are especially used for the termination of specific links.  Where as the configuration packet used for the link establishment.  The link monitoring and Debugging packets are for the purpose of managing  the link or to debug the link.