Data packet numbering in packet-switched data transmission

A telecommunication system comprising a mobile station and a first and a second wireless telecommunication network, which are arranged in a packet-switched data transmission to transfer a responsibility for a connection (handover) from a connection between said mobile station and said first wireless telecommunication network to a connection between said mobile station and said second wireless telecommunication network, in which first wireless telecommunication network a data packet number space available for data packet numbering is bigger than a data packet number space of the second wireless telecommunication network, wherein in the first wireless telecommunication network data packet numbering is arranged to be restricted such that numbers of the data packets of the first wireless telecommunication network do not exceed a maximum value of the data packet number space of the second wireless telecommunication network.

A terminal for a packet-switched telecommunication system, said terminal being arranged in a packet-switched data transmission to transfer a responsibility for a connection (handover) from a connection between said mobile station and a first wireless telecommunication network to a connection between said mobile station and a second wireless telecommunication, in which first wireless telecommunication network a data packet number space available for data packet numbering is bigger than a data packet number space of the second wireless telecommunication network, wherein the terminal is arranged to restrict data packet numbering of the data packets to be transmitted such that numbers of the data packets do not exceed a maximum value of the data packet number space of the second wireless telecommunication network.

A network element of a first wireless telecommunication system, said network element being arranged to control data packet numbering in a packet-switched data transmission connection between a mobile station and said first wireless telecommunication network, wherein

• said network element is arranged, when a responsibility for a connection is transferred (handover) from a connection between said mobile station and said first wireless telecommunication network to a connection between said mobile station and a second wireless telecommunication network having smaller data packet number space available for data packet numbering than in the first wireless telecommunication network, to restrict data packet numbering of the data packets to be transmitted such that numbers of the data packets do not exceed a maximum value of the data packet number space of the second wireless telecommunication network.