The 10GBase-LR is 1310nm and the QSFP-40G-LR4 CWDM channels are 1271, 1291, 1311 and 1331 nm. Are the 1310nm and 3rd channel 1311nm technically compatible?

I have a 10Gb and (will eventually have) a 40Gb switch both fitted with basic LR (Q)SFP+ transceivers and want to know if I can directly connect them or will I have to use an adapter to fit an SFP+ in an QSFP+ port?

I’m looking at using the XQX2502 QSFP+.

  • gramathy@lemmy.ml
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    1 year ago

    Unless specifically stated, generally fiber transceivers only run at the stated rate and would expect every channel to negotiate unless it had a 4x10 mode supported by both the transceiver and the device you put it in (which is what that DAC splitter is for), though once you split the lanes this way, a single pair would only ever run at 10g

    Additionally the nature of CWDM on a single pair means the 10g side will see all four signals simultaneously as there are no filters on that side of the connection. QSFP+ runs like this because it’s cheaper to manufacture and a single transmit/receive pair is only necessary in much longer range transport which typically uses more specialized expensive hardware for better long range signal integrity.

    In short: no, this won’t work and transceivers generally only ever run in one mode et once as configure by the switch/router they’re inserted in, and the modes you’re asking a qsfp+ to run in are mutually exclusive based on type (single lc pair cwdm at 40g vs 4x10g MPO/MTP with changeable modes). Fiber doesn’t have the same “negotiation” features that copper Ethernet does.

    • Sailing7@lemmy.ml
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      1 year ago

      I didnt ask his question, though i a want to thank you for answering it. I learned a lot in this thread :D