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    Mixed MM and SM fiber

    Evening all,

    I have been thinking about our internet connection set-up and need some input/advice.

    Our main centre has a multi-mode fiber backbone running through it, connecting our various switches/pbx and leased line.

    BT I think use single mode runs on their equipment, so our setup at the moment sees the incoming fiber(from the white tray) going into a fiber patch panel and then sent up to the main comms room, so single mode cable(if BT do indeed use single) into a multi-mode patch and in the comms room, what I assume is a single mode cable to the BT NTE(BT engineer provided this patch lead). Only a short run though, probably less than 20m, but then again, who knows what route it takes, could be 30m if it goes around the houses first. We didn't install it, Nokia did, who owned the building before us(was their UK HQ at one point).

    Now this works and provides our 100mbit connection, but I do see problems on its usage, such as downloads failing and having to constantly retry, until we hit a 'sweet spot' and it downloads, and 'applications' such as the BigBlueButton being useless for voice. I assume it works because the fiber runs are so short in the big scheme of fiber lengths. I have no fiber testing equipment, so can't actively go checking for errors. (Gaffer taping a 8p8c tester and a maglite to the fiber end doesn't work for some reason )

    Should I be using mode conditioning cables at either end of the patch panel to convert single to multi and back again? (I know not perfect, but I can't rip out the multi and replace with single, nor do I want to try and find the routes to run a single mode fiber just for the leased line) Are my problems something that can be caused by this setup(crc errors etc)? I have read that setups like our current one lose a lot of power with the wrong type fiber, but havent had any definitive feedback, BT toe the party line and say that anything not to their guidelines isn't supported, so wont help or look into it(Thanks BT). We pushed the engineer to connect it up like this, so our(read:my) problem! I'm only now coming back to it, now i've got more time to see if it can be done better, you know how it is, need to get a building up and running quickly, no time to troubleshoot as long as it works.

    Day to day running seems fine from a user point of view, but things are mostly light, its just the little things like large(sometimes not though) downloads and the BBB voice thing, which would be nice to be ruled out as a fiber issue, so I can move on to other avenues of enquiry.

    Any input from people who know more about fiber would be helpful.

    I may just buy some conditioners and test it out, but some of those things can be £50 - £100 for 3m. I have seen some cheaper ones, but not sure on quality, to be honest.

    Thanks

    James

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    Signal loss from mismatched cables is huge and conditioners probably won't help that much. You can check for errors on the internet device looking for packet errors etc.

    What you could do is either move the singlemode internet device into the room where the single mode terminates and then connect that back to the other room with propper multimode SPFs or chuck a switch in the middle with a single mode and a multimode spf in their own vlan to act as a repeater/media converter to push it over the other fibre correctly.

    TBH is is probably cheaper and less hassle to just put single mode fibre through if this is infact your problem (check error rates on gateway device to be sure).

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    Thanks for that, not the cheery news I was after to be honest, but that's life and wiring protocols!

    I saw this http://www.transition.com/MyTNConnection/?p=120 and thought it looked like the solution.

    Running SM fiber through a concrete sub structure between different floors makes me ill just thinking about it! Cant move the WG down to the other cabinet, as it needs to be in the comms room to receive the server connections to the optional interfaces. SMT won't authorise a switch and SPF's just for this(I shouldn't think), so that's out. Was really hoping media conditioners would be the way forward as the run is so short

    Just had a look on the Watchguard and it is showing 48 errors on the trusted interface, 6 on one of the optionals, and none on the others including the external interface connected to the BT equipment. I suppose it is the middle of the night though! Maybe it isn't the mixed fiber causing a problem.

    I will have to initiate a large http download tomorrow and see what happens.

    Thinking about it, its mainly the MS VLSC I have problems downloading from, with download manager and browser. Its probably an MS problem knowing my luck! Doesnt explain crap voice in BBB though, but that could be a multitude of other things entirely.

    Thanks for the reply

    James



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