Data packet shortening method and device

A data packet shortening method for shortening data packets passed between first and second devices. The data packets include address data which is sent from the first device to the second device and returned to the first device unchanged. The address data is temporarily stored at an address of a memory device, and the address data and the address of that data in the memory device is sent from the first device to the second device. When it is necessary to communicate the address data from the second device to the first device a data packet is sent which includes the address of that data in the memory device but does not include the actual address data. The required address data is derived by the first device from the address of that data in the memory device.