Synchronization of data packet numbers in packet-switched data transmission

A method for acknowledged transmission of data packets in a packet-switched telecommunications system, the telecommunications protocol of which comprises a convergence protocol layer for converting user data packets into convergence protocol packets, and a link layer for sending convergence protocol packets as data units and for acknowledging the transmission, the method comprising

• defining a data packet number for the convergence protocol packets to be transmitted by means of counters of the sender and the receiver which are synchronized with each other, in which case the transmitted convergence protocol packets are acknowledged with said counter values,
• defining that convergence protocol packets containing only user data are to be used in the data transmission between the sender and the receiver,
• sending, in response to asynchronization of said counters, convergence protocol packets which contain a packet data number, and indicating the number of said convergence protocol packets to the receiver, and
• synchronizing said counters on the basis of the data packet numbers included in said convergence protocol packets.