The Bit Error Rate (BER) is the ratio of the number of binary
signal elements corrupted during transmission to the total number of binary signal elements sent out. A bit error rate of 1 means that every bit is wrong. An error rate of 6x10exp-6 means that on average 6 bits can be wrong when 1 million bits are transmitted. For different local area networks, the standard prescribes different values for the bit error rate: For Ethernet, the standard requires a BER value of 10exp-8; for Token Ring, 10exp-9; and for FDDI
, 2.5 x 10exp-12. This means that for FDDI, there is one erroneous bit for every 400 billion bits transmitted.