CDF stands for "Charging Data Function". It is a key component in the mobile network charging and billing architecture.

The CDF is responsible for collecting charging data records (CDRs) from various network elements. These CDRs contain information about the usage of network resources by the network users.

Then the CDF aggregates and correlates the collected CDRs. It then transfers the processed CDRs to the Charging Gateway Function (CGF).

In most cases the CDF is integrated into the network elements that generate CDRs, such as the GGSN, the S-GW, or the P-GW.