Re: packet error rate

In article <1139380314.818253.132610@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
fangyong.F@xxxxxxxxx <fangyong.F@xxxxxxxxx> wrote:
For analysing the quality of firewall, I want to collect network
statistic data and calculate packet error rate(PER). But I don't know
the threshold of PER which means the network becoming bad.

There is no hard threshold. The higher the PER, the more likely
it is that you are going to require an end-to-end TCP retransmission.

If you are not using SACK (Selective ACK) then a TCP retransmission
involves also retransmitting everything for that connection that went
into the pipeline between the time that packet was sent and the NAK
was received; it is not so much the extra volume but the latency
involved that ruins your throughput.

Ethernet is, if I recall correctly, designed for an error rate
of around 1 in 1E10 bits (10,000,000,000 bits) -- which is around
11 seconds of transmissions at gigabit rates and less than 2 minutes
at 100 megabits. (Remember that the rate applies to -all- bits
transmitted, not just payload, and not just those involved
in any one TCP connection.)