Measuring Bit Error Rate on 2x Tetrapolis or 2x Inferno

Requirements

A running Ronja Tetrapolis or Ronja Inferno link
IP networking on the link set up
PC connected to one side of the link by full-duplex wired or fiber optic network.
ping program installed

You can select payload length in ping. The flag for this selection varies depending on ping vendor. Select suitable one to get packetloss between 0% and 100%. 56 bytes are default. Use max. 1472.
If you have neither scientific calculator, nor access to www nor local running copy of Ronja web, then select only 14, 56, or 1472 bytes of ping payload
If the ping allows you to specify -c to send packet as soon as the previous one arrives, use this flag.
If you are using the -c flag, then run two instances of the ping at the same time (in different xterm windows or consoles).
Do not use the -f (flood ping) option. This would render the measured BER invalid.
Leave the ping to run long enough to have multiple dropped packets. The longer the better precision.
Press ctrl-c and read out the packetloss (in %)

Online BER calculator
If ping payload is 14, 56, or 1472, use the graph, page 22 (PDF), (PostScript) with the correspondence between ping payload and ethernet payload

Ping payload Ethernet payload
14 42
56 84
1472 1500
1. nbits=8*ping_payload+400
2. bgr=(1-packetloss/100)^nbits, where packetloss is in % (from 0 to 100) and x^y means x powered (exponentiated) to y
3. ber=1-bgr