Frame Error Rate vs Bit Error Rate

There are multiple ways in which the quality of networking products can be assessed. Two
clearly defined techniques are the measurement of bit error rate (BER) and frame error rate
(FER). Many networking products are specified with the bit error rate that they achieve or
support. BER is simply the ratio of bits that have been incorrectly received to the total number
of bits sent. The test is performed by sending strings of pseudo-randomly generated bits
through the device.

Frame error rate (FER) is a better test for two reasons:

1. In real-world Ethernet networks, the basic data unit is a frame, a collection of bits arranged in a format consistent with the Ethernet standard. A frame can contain between 512 and 12,144 bits per the Ethernet standard. If a switch or a NIC receives a frame with one or many incorrectly transmitted bits, the complete frame will be discarded. The degradation of network performance due to dropped frames is the same for one or many bit errors within a frame. BER does not account for this fact.
2. FER testing takes longer to complete. Berk-Tek performs FER testing for a minimum of one hour per test, whereas a BER test would
   take about two (2) minutes. This increased test time is significant because it allows the hardware and cabling to reach operating
   temperatures. The performance of networking products decreases as the temperature increases. Robust performance is, therefore, better verified during longer tests that allow for transceivers, switches, cabling, etc., to reach their true operating temperature.

Source: www.berktek.us