MikroTik S-RJ01 SFP real speed

Hardware
1

Hi everyone,

I’m concerned about real speed of S-RJ01 module. SFP spec allows up to 4 Gbps I think, and website mentions “1.25Gbps”, but at the same time there’s “Gigabit” all over the place.

My goal is to connect two 260GS switches via SFP ports, and I’m wondering whether I’ll have 1 gig or 1.25 gigs between them.

Thank you!

2

Marketing :slight_smile:

1.25Gb is pure speed including coding/decoding/synchronization/etc. overhead bits needed to transmit data.
Usable is 1Gb

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3

Ethernet connections have a negotiated speed, and these speeds are fixed.
The S-RJ01 will be capable of negotatiating at 10/100/1000 Mbit speeds.

And the RB260GS has a SFP (not SFP+) port, so again the max speed is 1 Gbit.
The 1.25 Gb is probably the "raw" speed, including overhead and what not, the data transfer will max at 1 Gb

However, if you can (i.e. your two RB260GS are not too far apart) it would be better if you would avoid the the SFP modules and use instead a DAC or DAO cable, which usually run cooler than SFP copper modules.

Even if the 1Gb modules like the S-RJ01 are not particularly power hungry - please read as heat generating - a direct or optical connection will likely produce less heat, which in passive cooled devices like the RB260Gs is a very good thing.

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4

Thanks for the suggestion. In my case I already have a cable in the building, replacing it with DAC is not feasible. Also I’ve found a cheaper SFP (not original MikroTik) and the only difference is that I don’t have a temperature reading

5

The 1Gb/1.25Gb silliness comes from the fact that serial transmission on the sfp is done using 8b10b coding that encodes every 8 bit word into a 10 bit symbol. This leads to the +25% signalling speed. The encoding ensures both that the signal is dc balanced (not a concern here) and also ensures clock recovery (which is very much a concern.)

In the old days when words actually meant something... (mumbles something in old) this sort of channel was referred to as 1Gbps, counting the useful data, at 1.25Gbauds, counting the signalling states.

6

Real comment, I have them in use:
1Gb is the max you get ( actually 950Mbps-ish).

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