# Non-standard facilities frame

ITU T.30 allows a non-standard message (one not defined in T.300) to be included with most negotiations. These non-standard frames are called NSF when the called fax terminal sends DIS, NSS when the calling fax terminal responds to DIS with DCS, and NSC when commanding the called fax terminal to send (a poll).

A non-standard frame begins with the country code of the manufacturer, the manufacturer's code, and any additional ASCII information. Limited by a maximum allowable transmission time of three seconds per frame. The non-standard frame transmitted by the remote terminal is read only if the first three bytes match the country code and manufacturer's ID parameters for this terminal.

Some manufacturers use non-standard messages to negotiate use of proprietary features when two machines with the same manufacturer's ID code fax to each other.