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Wireless Networks Thread, Fiber Coupling Query in Technical; Originally Posted by bossman @CyberNerd: As I have said all my switches are Cisco and I have a OM3 fibre ...
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    Quote Originally Posted by bossman View Post
    @CyberNerd:

    As I have said all my switches are Cisco and I have a OM3 fibre backbone and switch links, my servers due to the school insisting I move them have cat6E copper links back to the core switch and I have had no degradation whatsoever and the cost was minuscule compared to fibre costs and also with no gain from installing fibre it was a no brainer.

    I too have done the CCNA and some of what it teaches can be taken with a pinch of salt.
    yes. i know what you mean. I was talking from an 'ideal' perspective, and I am pretty sure that in an ideal situation that external buildings should be linked by armoured fibre.
    I think srochfords explanation of electrical phases is the reason.

    Cat5e or Cat6 will work, I am sure of that, but where do you draw the line?

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    bossman's Avatar
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    @CyberNerd:

    Agree with you armoured fibre should be the norm but in this case I would advise the cat5E or cat6 for cost and outcome purposes.

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    Quote Originally Posted by bossman View Post
    Agree with you armoured fibre should be the norm but in this case I would advise the cat5E or cat6 for cost and outcome purposes.
    But if, as Geoff says, it is illegal due to Building Regulations; then copper will be (or should be) out of the question.

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    Jamman960's Avatar
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    Just checked all the patch cables, they're 50/125 and so is the 8core cable(luckily... was installed before I joined)

    At the moment the switch in the 2nd building has 2 Gbic/GigE ports and is linking to 3 buildings - 1 via Fiber, 2 via Cat5E so one is currently only connected at 100mbps. In theory if I could move the closer building over to Fiber & bypass the switch in that building I could then move the other building over to the GigE port and be closer to a star topology.

    I've worked out that I'd only have to spend around 50 on additional patch cables & couplers so it may still be worth going ahead with. The couplers I've seen are 2.99 each(ebay), based on losing 0.5db per connection I'd probably lose around 3db - is that too much?

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    What Loss Should You Get When Testing Cables?
    While it is difficult to generalise, here are some guidelines:

    -For each connector, figure 0.5 dB loss (0.7 max)
    -For each splice, figure 0.2 dB
    -For multimode Fibre, the loss is about 3 dB per km for 850 nm sources, 1 dB per km for 1300 nm. This roughly translates into a loss of 0.1 dB per 100 feet for 850 nm, 0.1 dB per 300 feet for 1300 nm.
    -For singlemode Fibre, the loss is about 0.5 dB per km for 1300 nm sources, 0.4 dB per km for 1550 nm. This roughly translates into a loss of 0.1 dB per 600 feet for 1300 nm, 0.1 dB per 750 feet for 1300 nm.
    So for the loss of a cable plant, calculate the approximate loss as:

    (0.5 dB x number of connectors) + (0.2 dB x number of splices) + Fibre loss on the total length of cable
    Fiber Optics - Testing


    3db should be ok - just like running a 1km cable
    TBH I'm not sure what the 'actual' figures should be - I guess it depends on the fibre modules.

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    That many couplers are going to cause trouble, you have a very limited power budget with fibre and connectors are the worst as they drain a huge amount of that power and can add jitter. You also have the issue of all of the additional places for dust to get in. At most I would suggest a patch - fibre - patch - fibre - patch where the two fibres are prepperly installed and speced fibre.

    You may be able to manage it depending on the quality of the fibre and the connectors on each bit but it will always be a vunrable point where little things like vibration jaring the conectors or dust may compromise it.

    If it is not to much of an investment then it may be worth a go though as a temporary solution until better cable is avalible. The idea would be to connect it all up then go onto the switch managment pages for the switches at each end. Clear the port counters then send several really large files over the link. Once you have done that check the switch pages for errors on the ports in question. There should be none, if there are look for a different solution, if not then it may well work properly for some time.

    The issues with running copper between building are real especially for above ground cable which can be affected with lightning and fry two switches rather than one let alone the nasty potential voltage that can be generated between two differing ground points and/or phases.

    EDIT: Can't find the spec for multimode but the low end single mode stuff - which is more powerful - seems to have a power budget of around 10.5dB ftp://files.dlink.com.au/products/DE...tasheet_04.pdf
    Last edited by SYNACK; 29th July 2009 at 12:38 PM.

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    Quote Originally Posted by webman View Post
    But if, as Geoff says, it is illegal due to Building Regulations; then copper will be (or should be) out of the question.
    I agree also with what Geoff states but it is only advice based on costs and outcome not legalities, if it has to conform to wiring regulations then there is only one option and that is armoured fibre.

    Case closed

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    Quote Originally Posted by bossman View Post
    I agree also with what Geoff states but it is only advice based on costs and outcome not legalities, if it has to conform to wiring regulations then there is only one option and that is armoured fibre.
    So we can ignore the legalities as long as we do something for cost reasons (and 'outcome', whatever that means exactly )?

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    We have a science block that was originally connected (blatantly illegally) via overhead cat5e I was replacing the switches either end after about every 6 months due to each port sequentially getting blown.

    Needless to say they now have a nice overhead OM3.

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    Quote Originally Posted by webman View Post
    So we can ignore the legalities as long as we do something for cost reasons (and 'outcome', whatever that means exactly )?
    Not at all that is not what I am saying far from it, if you look at the scenario it states that 50m is underground and this is what I was referring to, as for the rest it is a logical decision based on his requirements and that is around 140m of fibre albeit patched.

    In my honest opinion I would go for copper underground 50m as stated and the rest get someone in to fibre overhead in one link and thus cut down on the need to join everywhere.

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    Quite apart from the possible electrical differential you'll appreciate that you put in fiber then next time you need more switching or more bandwidth.

    If you making the effort to pull fiber make sure you put in more than one (even better terminate them to another patch panel), you can never have too much connectivity.

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