Data transmission system in a communication network, the communication network comprising a satellite transmission link, a service provider part, a user part and a satellite access network comprising a collection point PoP adapted to dispatch data flows, the data transmission system comprising several gateways comprising a radiofrequency part, and said system further comprising a modulator of data to be transmitted comprising at least one emission back part located in a baseband part and an emission front part located in the radiofrequency part: • said emission back part being positioned at the collection PoP point part and comprising the following modules: • an NCR network clock reference module adapted to take into account an external absolute time reference to reconstitute a network clock for a synchronization in the data transmission and a emitter module, said NCR module being adapted to supply to the emitter module, at the start of a new hyper-frame to be sent, a current date value NCR to be inserted in a data field of the hyper-frame under construction, the start of said new hyper-frame being indicated by a revised H.F.T x trigger information of said emitter module, • said emitter module being adapted to receive the value of said NCR date, to insert it into a data packet to be transmitted to the emission front part and to emit to the NCR module the information H.F.T x trigger on a t sync synchronization instant for a receiver module of the front emission part, • said emission front part being positioned in the radiofrequency part of a gateway and comprising the following modules: • the receiver module being adapted to generate several pieces of information towards a module for reconstructing a clock for synchronizing and reading the data, said information containing: information on the latency of the transmission link between the emission back part and the emission front part, information on the arrival time t a of said data packet emitted by the emission back part, signaled by an H.F.R x trigger signal, and an H.F.R x NCR information corresponding to the value of the NCR date extracted from the data packet and corresponding to the start of the received hyper-frame to be taken into account on receipt of the H.F.R x trigger information in order to reconstitute locally at the radiofrequency part a clock corrected for the transmission latency between the emission back part and the emission front part of the modulator, • the reconstruction module adapted to reconstruct a clock locally from the latency value of the transmission link, the value of the NCR date contained in the transmitted data and the arrival time t a of the data packet, • an insertion module adapted to insert the local clock reconstructed in a data packet received by the receiver before transmission of the modulated data via the satellite, • the emission back part and the emission front part being adapted to exchange encapsulated data according to a protocol used for the transmission of data in the system. • said emission back part being positioned at the collection PoP point part and comprising the following modules: • an NCR network clock reference module adapted to take into account an external absolute time reference to reconstitute a network clock for a synchronization in the data transmission and a emitter module, said NCR module being adapted to supply to the emitter module, at the start of a new hyper-frame to be sent, a current date value NCR to be inserted in a data field of the hyper-frame under construction, the start of said new hyper-frame being indicated by a revised H.F.T x trigger information of said emitter module, • said emitter module being adapted to receive the value of said NCR date, to insert it into a data packet to be transmitted to the emission front part and to emit to the NCR module the information H.F.T x trigger on a t sync synchronization instant for a receiver module of the front emission part, • said emission front part being positioned in the radiofrequency part of a gateway and comprising the following modules: • the receiver module being adapted to generate several pieces of information towards a module for reconstructing a clock for synchronizing and reading the data, said information containing: information on the latency of the transmission link between the emission back part and the emission front part, information on the arrival time t a of said data packet emitted by the emission back part, signaled by an H.F.R x trigger signal, and an H.F.R x NCR information corresponding to the value of the NCR date extracted from the data packet and corresponding to the start of the received hyper-frame to be taken into account on receipt of the H.F.R x trigger information in order to reconstitute locally at the radiofrequency part a clock corrected for the transmission latency between the emission back part and the emission front part of the modulator, • the reconstruction module adapted to reconstruct a clock locally from the latency value of the transmission link, the value of the NCR date contained in the transmitted data and the arrival time t a of the data packet, • an insertion module adapted to insert the local clock reconstructed in a data packet received by the receiver before transmission of the modulated data via the satellite, • the emission back part and the emission front part being adapted to exchange encapsulated data according to a protocol used for the transmission of data in the system.