Transmission timing for data packets transmitted from an internet terminal to a terminal in a cellular radio network

A method for transferring data over a communication link from a first unit (e.g. an Internet terminal) to a second unit (e.g. alterminal in a cellular radio network), the link comprising a first portion across which the data is carried by the transmission of data packets at regular intervals (e.g. the radio network) , and a second portion between the first portion and the first unit over which the data is carried in a form that is not synchronised with the transmission of data packets over the first portion (e.g. a packet switched network such as an IP network); the method comprising transmitting to the first unit time alignment information regarding the times at which packets are to be transmitted over the first portion.