The present invention provides a method, a system, a node in a communications system and a computer program facilitating a data transmission from a push service provider that addresses data by an Internet protocol address to a receiver which is identified in a communications system by a subscriber identity different to the IP address. The subscriber identity is determined by use of a first portion of the IP address for a look-up of a first portion of the subscriber identity, and by an assignment of a second portion of the IP address to a second portion of the subscriber identity. The invention can be used for different IP address formats like IPv4 and IPv6 addresses. The invention can be used in GSM/GPRS systems, PDC/PPDC and UMTS systems.