Currently I see three types of 1Gbps copper SFP modules at the same store:

  • "SFP 1000BASE-T"
  • "SFP 10/100/1000BASE-T | SGMII"
  • "SFP 10/100/1000BASE-T | SGMII | Rx LOS"

If the switch documentation does not say explicitly (other than saying "1Gbps SFP port"), should I always assume that SGMII (whatever that is in context) is not supported and get the 1Gbps-only, non-SGMII kind?

(How are the 'Rx LOS' modules functionally different from the others? Does it just mean they can report when the link is down, or something else?

1 Answer 1


Most 1G SFP modules are fed with a 1000BASE-X data stream created by the PCS sublayer. A 1000BASE-T SFP module then has to transcode that -X to a four-lane -T signal.

Some host devices, especially NICs, instead use a lower-level SGMII signal (serial gigabit media-independent interface). xMII is an optional interface between the MAC and the PHY layer.

Rx_LOS is an SFP slot signal - quoting from Seagate's INF-8074i spec:

LOS (Loss of Signal) is an open collector/drain output, which should be pulled up with a 4.7K – 10KΩ resistor. Pull up voltage between 2.0V and VccT, R+0.3V. When high, this output indicates the received optical power is below the worst-case receiver sensitivity (as defined by the standard in use). Low indicates normal operation. In the low state, the output will be pulled to < 0.8V. 6) VeeR and VeeT may be internally connected

For an SFP module that options means that there's a real LOS signal presented to the host device, instead of simply pulling it low permanently.

Can't be sure, but judging from nothing of this being mentioned in the switch documentation, I'd guess you need a plain 1000BASE-T module. However, do make sure that 1000BASE-T is supported in that SFP slot. Not all devices do.

  • Does the lack of "Rx_LOS" on some of the product listings mean they can't indicate the link being down, or is there another SFP signal for that – or would it be just an omission in the marketing? Dec 20, 2023 at 5:29

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