Following is a summary of the various state variables and parameters used by the protocol. They are separated into classes of system variables, which relate to the operating system environment and local-clock mechanism; peer variables, which represent the state of the protocol
machine specific to each peer; packet variables, which represent the contents of the NTP message; and parameters, which represent fixed configuration constants for all implementations of the current version. For each class the description of the variable is followed by its name and the procedure or
value which controls it. Note that variables are in lower case, while parameters are in upper case. Additional details on formats and use are presented in later sections and Appendices.