QSFP-100GE operation

[JOS3]

Hello
I would like to know how the 4 lines of the QSFP-100GE modules work, with respect to power. As we observe when checking the power, the four lines appear with different powers and we would like to know if one of the lines goes out of the power range or stops working, how does the QSFP behave, does it decrease its transmission power to 75GE, does it show a Warnnig in the equipment log, does it stop working?

[hrtendrup]

Hello,

First, I think you might need to be a bit more specific about which 100G transceiver you're referring to.

I use this link all the time to get medium-level tech specs for the 100G optics Cisco manufactures: 100GBASE QSFP-100G Modules Data Sheet - Cisco

Next, optics are generally either 2 fiber (LC) or 12 fiber (MPO)*.

2 Fiber optics will use different wavelengths of light to channelize the transmission medium. In that case if either of the fibers are cut, the link will be marked as down by one side or the other and the whole link will non-functional, either hard-down by UDLD or only passing traffic in one direction, likely causing so much trouble as to be effectively non-functional.

12 fiber optics (only 8 are actually used) use a bit-spray technique where the bandwidth is spread across multiple pairs of fibers contained within a bundle. I'm not actually sure what might happen if one of those pairs were somehow severed, but not the others if in non-breakout mode. I don't know if it's documented how the link-layer is determined. If the patch is in break-out mode, it's easier to imagine one pair being severed but not others. In that case the main optic would reduce its bandwidth by the number of failed sub-links (broken-out links, child links, pick your moniker) 

*I won't dismiss that there may be other optics that utilize some other number of fibers, but 2 or 12 is the vast majority, no?

[JOS3]

Hello, the specific module would be the QSFP-100G-SR4-S.

[hrtendrup]

Ah, yes the ~SR4s use 8 pair out of a 12 fiber MTP/MPO patch. These can be broken out into 4x25G interfaces of 2 fibers, Tx/Rx. In that case the bandwidth of the parent interface would be reduced if a fiber were damaged on one of the child interfaces. In a non-broken-out link (QSFP-100G-SR4-S to QSFP-100G-SR4-S to), I have a hard time imagining a single fiber being damaged inside the 12 fiber sheath. I don't actually know how the optic would behave....badly, at best.