【BPI-R3】about SFP rate

Hello everyone, I am a newer about SFP. I have some question about SFP speed. I use 2.5G opitical module with fiber to connect two of BPI-R3, and then I used iperf3 to test the rate between the two of BPI-R3. The test result is that the average rate is 2.35Gbps, this result is ok for RJ45, I wonder if this is a normal result for SFP as well, or SFP maybe higher? I think my question may be too simple, but because I am a newer about SFP. I hope someone can answer my question, thanks a lot!

sfp is “only” a medium converter…electrical - optical/electrical. There are some that do a bit more (having a phy for doing e.g. autonegotiation independ from the host-interface)

which fibre-sfp do you have? have not found a fibre 2.5g yet. Can it operate at 1G too?

you have to know that the speed of 2.5G is for all data…if you do iperf or similar you see only the payload-speed, not the headers (ethernet,IP,tcp) which need to be also transmitted…this is the cause you only get 2.35Gbps. If packets are smaller, you need more packets and so more headers which limits the payload-speed more

Thanks for your reply.

My fiber-sfp is 2.5G, I have check with ethtool, it tell me that it suppport 2500Base-X and 1000Base-x. But I haven’t tried switching to 1G yet. I am in CN, this module is made by Kingsignal SFP Transceivers Kingsignal Technology

So if I use iperf to test rate, it doesn’t take the headers into account when it calculates the rate. What ever transmission medium is, if mac only support 2.5G, the maximum speed I can see from iperf is around 2.35Gbps, am I right?

Can we get this sfp on aliexpress or similar? Have not found any store for it

Afaik Iperf can only calc the payload by time and this does not include headers which have to be transferred too

I’m afraid you can’t, I bought this by the salesman from Kingsignal, as I know, they don’t have any online stores.

Thank you very much for your reply!