Link Maintenance Frames

Link maintenance frames are transmitted periodically to test and maintain the link. The link termination frames are:

• Code-reject

  Code 0x07. Rejects an LCP frame that has an invalid code field.

• Protocol-reject

  Code 0x08. Rejects a PPP frame that has an invalid protocol id.

• Echo-request

  Code 0x09. Requests a response, in the form of an Echo-reply frame, from the remote end-point. Used to test that the link is still up.

• Echo-reply

  Code 0x10. Responds to a valid Echo-request frame. Used to test that the link is still up.

• Discard-request

  Code 0x11. Sends a frame which is silently discarded at the remote endpoint. Used as a debugging mechanism.