The main task of this dissertation was the modification of Gy interface (OCS) scripts in “C” so that it supports error codes in CCR – I (Initial) messages. Development was needed in order the error code value to be configurable by the user. The configurable error code value to be sent for a configurable percentage of CCR messages. The second task was the modification of Gx interface (PCRF) script in “Pearl” so that it supports error codes in CCR – I (Initial) message. The error code value should be configurable by the user. The configurable error code value to be sent for a configurable percentage of CCR messages. For the purpose of our tests after the modification of scripts we used the 4G lab environment of Nokia. We modified as we mentioned above the OCS scripts that NOKIA uses for Gy interface in order to add the option for user to choose the error code that he wants to reject the new session that its state is still on-going. We also write a whole library with as much error codes as the script can support. Another task of this thesis was to do the same modification for PCRF scripts in Pearl in order the script supports the addition of a specific error code inside the CCR-I message. The final task was the participation in an inside new created team that its task was the creation of a PCRF script in C from scratch.