This Recommendation provides specifications for the ways in which facsimile calls can be non-intrusively monitored. Non-intrusive fax performance monitoring is done from within a network, and can provide a broad view of fax performance over the network being monitored. These are some significant differences between end-to-end fax performance measurement and non-intrusive measurement. The chief advantage of non-intrusive measurements is that they provide a view of performance encompassing a range of physical locations and terminals that cannot be practically achieved when testing end-to-end.