Embodiments herein relate to a method performed by a transmitting device (12) for transferring background user data to a receiving device (10) in a communication network (1). The transmitting device (12) intercepts a packet, which packet comprises foreground user data in a payload field of the packet. The transmitting device (12) determines that the packet is intended for the receiving device (10). The transmitting device (12) establishes an available amount of data in the payload field of the packet. The transmitting device (12) adds the background user data for the receiving device (10) to the established available amount of data in the payload field. The transmitting device (12) transmits the packet with the foreground user data and the background user data to the receiving device (10).