NAFC ,Network Adapter Feedback Control, is a method to regulate the upload speed automatically, like USS. It was introduced in the Maella-Mod and is today implemented in the NeoMule-Mod, phoenix-Mod, Xtreme-Mod and ScarAngel-Mod.
To get the traffic of the modem, the traffic at the ethernet adapter is measured. This allows the upload to be fully used without saturating the modem.
This system compares with USS
This activates the Network-Adaptor-Feedback-Control, which calculates the uploadlimit according to the whole internet traffic of the network adaptor used by eMule. Using this option you will get a dynamic downloadlimit, if the upload is disturbed by other applications.
 What is "NAFC"?
The "Network Adaptor Feedback Control" orientates the eMule upload to the total upload of all applications, taken from the network adaptor. So the upload limit, adjusted in eMule, considers not only the data of eMule, but also every upload-packet of any application (webbrowser, onlinegames, FTP-upload, and so on). For instance: if you set your upload up to 15 kbs and your internet-telephony uses 5 kbs, eMule will send only 10kbs to data. Using this method, a much lower number of ping signals is guaranteed and your upload-capacity is used most effectively. If you use NAFC, you are able to adjust the upload-limit very close to the upload-capacity. The third image shows once again how the sum of upload data (1) + overhead + the rest of the networktraffic (3) result in the value adjusted at NAFC. To avoid any abuse of this feature, eMule checks if the measured data are data of eMule or of other applications. Are the sent data of eMule (data + overhead) smaller than 11 kbs, a download-limit will be switched on dynamically.
(this text is from old Xtreme homepage)
- Doesn't produce overhead (no pings are sent)
- Responds quickly, reaction time very fast <100 ms
- Very accurate
- Doesn't work with all operating systems (e.g. win95)
- Doesn't handle shared Internet connections as it can't monitor how much traffic is being used by other PC's.
- Doesn't respond to ISP slowdowns (unlike USS which can ping anything on the Internet).
- Requires user to know their maximum upload speed (USS detects it automatically)