Why do the SFP ports on UbiSwitch not work with my 1GBASE-T SFP Module?

– Rephrased from a custom email –

I see in the datasheet that UbiSwitch baseboard only supports 10GBASE-T SFPs. Does this mean these ports only work at 10G?

Not quite, though the answer is slightly nuanced.

This restriction does mean that you can only use an SFP that uses a 10GBASE-R interface on its “card-edge” side (the side that plugs into the SFP cage). This does restrict you to using 10G SFPs and means you can’t use a 1G SFP, that would use 1000BASE-R on its “card-edge” side.

While this does sound like it means that you can only use these ports for a 10G connection, the truth is that any 10GBASE-T SFP is going to support auto-negotiation on its RJ-45 side. So you could happily take a standard 10GBASE-T SFP and connect it to, say, a 100BASE-T ethernet port, and you’ll get a link at 100Mbps. In this case, the SFP handles the data rate conversion so that you get a working link at 100Mbps on UbiSwitch, even though the “card-edge” actual data rate is 10Gbps.

Of course this isn’t ideal, and will be solveable once our management interface is active on UbiSwitch, which would allow you to select the card edge speed. In the mean time what this means (at least in terms of a copper ethernet link) is that the only downside is the extra cost of buying a 10G copper SFP instead of a 1G copper SFP.

If you’re using something like a 10GBASE-LR, then you wouldn’t expect auto-negotiaton on that, and would expect to need a 10GBASE-LR on the other side. If you’re wanting to use a 1GBASE fiber mode, unfortunately that’s not going to work.

There is one work around however…

For ports 9 and 10, it is possible to cut a jumper on UbiSwitch to force the ports to go into 1000BASE-R mode. To do this, follow the steps below…

  1. Locate jumpers SM0 and SM1 on UbiSwitch

  2. SM1 is shorted, take a small knife and cut the track between the two pads.

  3. Ports 9 and 10 will now operating in 1000BASE-R mode, and will work with a 1G SFP.