CS 1000 supports Flexible Feature Codes (FFCs). The earliest model in the Northern Telecom digital Private Branch Exchange (PBX) explained special prefix digit string used to trigger special handling on a website. Later fixed feature code were introduced to request the desired feature. This approach was found to be limited in some cases. A digit pattern that was acceptable in one region was unacceptable in another region. So flexible feature codes feature was introduced to overcome this problem.

The Malicious Call Trace feature will be used as an example to explain the flexible feature codes:

The original CS 1000 Malicious Call Trace signaling used the special prefix, followed by the feature code 83. Rather than using the fixed digit pattern with CS 1000 FFCs, the user dials the digit pattern associated with the Malicious Call Trace (MTRC) FFC. The call trace is carried out.

The Communication Server has a similar model, with a call trace capability. It supports an FFC equivalent called as Feature Access Codes (FAC).

When CS 1000 FFC is mapped to the Communication Manager FAC, an analog endpoint user will not detect any difference. At the same time, digital and UNIStim endpoints can be assigned a Malicious Call Trace button, and when you press this button then FFC is not required. However, even digital and UNIStim endpoints can initiate transfer, enter the FFC, and carry out the trace. The ProVision tool extract the FFCs and map the respective FFC with the applicable FACs on the Communication Manager.