Data backup method and device

1. A data backup method, wherein the method is implemented by an intermediate device connecting first devices connected in a first network to a backup data storage server connected in a second network, comprising:

upon expiration of a first predetermined delay, first uploading, from the intermediate device to the backup data storage server, of a full backup archive built by the intermediate device from data stored by the first devices;

during the first uploading and upon expiration of a second predetermined delay that is shorter than the first predetermined delay, second uploading from the intermediate device to the backup data storage server, of at least one differential backup archive built by the intermediate device from data stored by the first devices, wherein each of the at least one differential backup archive that is uploaded in the second uploading is differential with regard to a latest completely uploaded full backup archive that is uploaded during the first uploading; and

the predetermined first delay and the predetermined second delay being determined as a function of a bit rate of an uplink connecting the intermediate device to a storage in the second network and as a function of a size of the at least one full backup archive and of the at least one differential backup archive.

2. The method according to claim 1 , wherein an uploaded full backup archive is only deleted from the backup data storage server when a full backup archive with a newer version is completely uploaded to the storage.

3. The method according to claim 1 , wherein the first network is a local area network and the second network is the Internet.

4. The method according to claim 1 , wherein the intermediate device is a gateway, giving the first devices connected in the first network access to the second network.

5. A device for backup of data stored by first devices connected in a first network to a backup data storage server connected in a second network, the device comprising:

a processor, a memory, a clock unit and at least one network interface, wherein the processor, the memory, the clock unit and the at least one network interface are configured to:

build a full backup archive from data stored by the first devices and for building of at least one differential backup archive from data stored by the first devices;

determine expiration of a first predetermined delay and of a second predetermined delay, the second predetermined delay being shorter than the first predetermined delay;

first upload to the backup data storage server, upon expiration of the first predetermined delay, of a full backup archive;

upload to the backup data storage server, during the first upload and upon expiration of the second predetermined delay, at least one differential backup archive, wherein each of the at least one differential backup archive that is uploaded is differential with regard to a latest completely uploaded full backup archive that is uploaded during the first upload; and

determine the first delay and the second delay as a function of a bit rate of an uplink connecting the intermediate device to a storage in the second network and as a function of a size of the at least one full backup archive and of the at least one differential backup archive.

6. The device according to claim 5 , wherein the processor, the memory, the clock unit and the at least one network interface are configured to delete an uploaded full backup archive from the backup data storage server when a full backup archive with a newer version is completely uploaded to the storage.

7. The device according to claim 5 , wherein the first network is a local area network and the second network is an Internet network.

8. The device according to claim 5 , wherein the intermediate device is a gateway giving the first devices connected in the first network access to the second network.