Method for verifying the integrity of data transmission between a main upstream unit and a main downstream unit, the method being characterized in that it comprises implementing the steps of: (a) Generation, by a data processing module of the main upstream unit, of a first frame comprising a data packet to be transmitted and a cyclic redundancy code of said packet, and transmission to an interface module of the main upstream unit; (b) Encapsulation, by said interface module of the main upstream unit, of the first frame in a second frame also including a cyclic redundancy code of the first frame; (c) Transmission of the second frame to interface modules (22a, 12b) of the main downstream unit and of at least one auxiliary upstream unit; (d) Extraction of the first frame from the second frame by the interface modules (22a, 12b) of the main downstream unit and of the at least one auxiliary upstream unit; and transmission to data processing modules (21a, 11b) of the main downstream unit and of the at least one auxiliary upstream unit; (e) Extraction of the packet from the first frame by the data processing module of the main downstream unit; and extraction of the cyclic redundancy code of packet by the data processing module of the at least one auxiliary upstream unit; (f) Encapsulation, by said interface module of the main upstream unit, of the cyclic redundancy code of packet in a third frame; (g) Transmission of the third frame to the interface module of the at least one auxiliary upstream unit; (h) Extraction of the cyclic redundancy code of packet from the third frame by the interface module of the at least one auxiliary upstream unit; and transmission to the data processing module of the at least one auxiliary upstream unit; (i) Comparison by the data processing module of the at least one auxiliary upstream unit of each of the cyclic redundancy codes extracted from the first frame and from the third frame; and confirmation of the integrity of data transmission to the main downstream unit only if comparison is positive. (a) Generation, by a data processing module of the main upstream unit, of a first frame comprising a data packet to be transmitted and a cyclic redundancy code of said packet, and transmission to an interface module of the main upstream unit; (b) Encapsulation, by said interface module of the main upstream unit, of the first frame in a second frame also including a cyclic redundancy code of the first frame; (c) Transmission of the second frame to interface modules (22a, 12b) of the main downstream unit and of at least one auxiliary upstream unit; (d) Extraction of the first frame from the second frame by the interface modules (22a, 12b) of the main downstream unit and of the at least one auxiliary upstream unit; and transmission to data processing modules (21a, 11b) of the main downstream unit and of the at least one auxiliary upstream unit; (e) Extraction of the packet from the first frame by the data processing module of the main downstream unit; and extraction of the cyclic redundancy code of packet by the data processing module of the at least one auxiliary upstream unit; (f) Encapsulation, by said interface module of the main upstream unit, of the cyclic redundancy code of packet in a third frame; (g) Transmission of the third frame to the interface module of the at least one auxiliary upstream unit; (h) Extraction of the cyclic redundancy code of packet from the third frame by the interface module of the at least one auxiliary upstream unit; and transmission to the data processing module of the at least one auxiliary upstream unit; (i) Comparison by the data processing module of the at least one auxiliary upstream unit of each of the cyclic redundancy codes extracted from the first frame and from the third frame; and confirmation of the integrity of data transmission to the main downstream unit only if comparison is positive.