Moi j'en suis sur, voila un extrait d'un de cours de Cisco sur la technologie ethernet 1000BASE-T
"Because Cat 5e cable can reliably carry up to 125 Mbps of traffic, getting 1000 Mbps (Gigabit) of bandwidth was a design challenge. The first step to accomplish 1000BASE-T is to use all four pairs of wires instead of the traditional two pairs of wires used by 10BASE-T and 100BASE-TX. This is done using complex circuitry to allow full duplex transmissions on the same wire pair. This provides 250 Mbps per pair. With all four-wire pairs, this provides the desired 1000 Mbps. Since the information travels simultaneously across the four paths, the circuitry has to divide frames at the transmitter and reassemble them at the receiver."
C'est boucoup plus complexe que 10/100, donc faire du 1000 avec une 10/100 par simple flashage de la puce, c'est pas possible sauf si ça avait été prévu avant.