EXFO ETS-1000 - Manual (Page 102)

Configuring and Starting a Test
94 ETS-1000
BERT
BERT
BERT (Bit Error Rate Test) test allows to measure bit error rate, the ratio of
errored bits to the total number of bits transmitted. To perform the test, a
specific binary pattern (known both to the source and destination) is
encapsulated into an Ethernet frame which is to be transmitted.
At the destination, the sent pattern is compared to the source one and then
the bit error rate is counted. To connect to the TDM-network, the interface
converter is used to convert packet network (Ethernet) traffic into the TDM
traffic format.
Testing can be performed at four layers of the OSI model.

At the Physical layer (Level 1) test data is send piecemeal with
specified interframe gap (IFG). In this case the test is performed from
the port A(B) to the port B(A) or using the Loopback function.

At the Data Link layer (Level 2), all data is encapsulated into an
Ethernet frame thus allowing to transmit test packets through a
network with the OSI’s second-layer equipment (for example, network
switch).