On some links it may be desirable to determine when, and how often, the link is dropping data. This process is called link quality monitoring.
This Configuration Option provides a method to negotiate the use of a specific protocol for link quality monitoring. By default, link quality monitoring is disabled.
The implementation sending the Configure-Request is indicating that it expects to receive monitoring information from its peer. If an implementation sends a Configure-Ack, then it is agreeing to send the specified protocol. An implementation receiving a Configure-Ack SHOULD expect the peer to send the acknowledged protocol.
There is no requirement that quality monitoring be full-duplex or that the same protocol be used in both directions. It is perfectly acceptable for different protocols to be used in each direction. This will, of course, depend on the specific protocols negotiated.
A summary of the Quality-Protocol Configuration Option format is shown below. The fields are transmitted from left to right.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Quality-Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data ... +-+-+-+-+
The Quality-Protocol field is two octets, and indicates the link quality monitoring protocol desired. Values for this field are always the same as the PPP Protocol field values for that same monitoring protocol.
Up-to-date values of the Quality-Protocol field are specified in the most recent "Assigned Numbers" RFC . Current values are assigned as follows:
Value (in hex) Protocol c025 Link Quality Report
The Data field is zero or more octets, and contains additional data as determined by the particular protocol.