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Wireless Networks Thread, Fiber Coupling Query in Technical; I'm hoping some one can help me, I've aquired a few 10m, 25m and 50m fiber patch cables which are ...
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    Jamman960's Avatar
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    Fiber Coupling Query

    I'm hoping some one can help me, I've aquired a few 10m, 25m and 50m fiber patch cables which are all LC-LC along with a few switches and GBICS/SFP's. I'm looking at running the 50m patch between two buildings which are close togeather and currently linked via Cat5e.

    The 2nd building has a fiber patch panel with 8 cores linked to our main building on the other side of the site via an overhead fiber link. The following is my current plan:

    50M LC-LC Fiber - 1st building to 2nd building via underground pipe
    LC-LC Coupler - Joining the 50m patch to the LC-ST Patch
    LC-ST Patch - Connecting between the coupler and the patch panel(2nd building)
    <Overhead 8core fiber> - 120M
    5M ST-LC - Connectiing the coupler and patch panel again(main building)
    LC-LC Coupler - Joining the 5M Patch to the final 10M patch
    10M LC-LC Fiber - Final connection to the Switch/Server room

    Total Distance ~190M

    Another option is to just go from the 1st building and connect straight to the switch in there via an LC-LC coupler and an LC-SC cable, a direct connection to the main switch would be prefered though... I'm just not sure how much extra latency will be introduced by the above plan.

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    distance is fine, what you need to watch for is the amount of decibel loss that you introduce from the extra connections. Each connector adds a loss of around 0.5db.
    maybe you could bypass the patch panel and use less couplers?
    Ideally you splice the connectors together rather than couple. but as the distance is short you might get away with it.

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    Geoff's Avatar
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    Also check the fibre in your patch cables are the same grade.

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    TNE
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    Are all the cables the same spec ie 50/125 or 62.5/125 as i dont think you can mix and match

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    I'm looking at running the 50m patch between two buildings which are close togeather and currently linked via Cat5e.
    If they're already linked and it works at 1000Mbps I don't see the point changing it for fibre. I'd only install it where there are lengths 90 metres + which is the getting towards the workable limit for CAT5e.

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    Quote Originally Posted by TNE View Post
    Are all the cables the same spec ie 50/125 or 62.5/125 as i dont think you can mix and match
    You can mix n match - it's just not advisable because it increases the decibel loss between the connections. you can go from 62.5 (Receiving) to 50 micron (transmission) with no loss but 50 microm (receiving) to 62.5 (transmission) incurs a 1-1.5 db loss. but yes, get the same grade if possible.


    Quote Originally Posted by Michael View Post
    If they're already linked and it works at 1000Mbps I don't see the point changing it for fibre. I'd only install it where there are lengths 90 metres + which is the getting towards the workable limit for CAT5e.
    Ideally, interconnected buildings should be linked by fibre.

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    Ideally, interconnected buildings should be linked by fibre.
    Why? Unless the length is greater than 100 metres you'll get zero benefit. It's also much, much cheaper. You also need fibre compatible switches or require to buy additional modules which you wouldn't need with CAT5e.

    I'd say the only exception would be if the area had very high electrical interference (for whatever reason) would I install fibre at shorter distances.
    Last edited by Michael; 29th July 2009 at 10:56 AM.

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    bossman's Avatar
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    @Michael:

    Totally agree with this advice, I would only look at going fibre if I was upgrading switch gear to run on 10Gb backbone and that wouldn't be too soon as the cost is still astronomical at the moment. I have OM3 fibre backbone and switch links already but the cost of the switches are too pricey at the moment.

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    Quote Originally Posted by Michael View Post
    Why? Unless the length is greater than 100 metres you'll get zero benefit. It's also much, much cheaper. You also need fibre compatible switches or require to buy additional modules which you wouldn't need with CAT5e.

    I'd say the only exception would be if the area had very high electrical interference (for whatever reason) would I install fibre at shorter differences.
    I was trying to think of the reason as I typed. It was definitely recommended on the CISCO CCNA course that I did, and I'm pretty sure the technical specifications for institutional infrastructure recommend the same thing, and probably a bunch of other wiring standards that I cannot remember. Perhaps it is for electrical interference, IIRC there is also something about voltage differentials between external buildings that needs to be considered.

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    bossman's Avatar
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    @Jamman960:

    You could also trunk cat5E cables to give you larger throughput which would be far less expensive and give you better throughput.

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    I think the main reason for not using copper between buildings even over short distances is if each building has a different earth connection, there is a potential voltage difference between the 2 earths, so the network cable could carry this voltage. (pretty unlikely though)

    Steve

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    Perhaps it is for electrical interference
    Well other than 10GbE, exceeding 100 metres or electrical interference I can't think of any other reason. In saying that even CAT6 can do 10GbE. To add to this, going from building to building you need external rated cable which is going to be more expensive.

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    @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.

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    Quote Originally Posted by steveg View Post
    I think the main reason for not using copper between buildings even over short distances is if each building has a different earth connection, there is a potential voltage difference between the 2 earths, so the network cable could carry this voltage. (pretty unlikely though)

    Steve
    It's actually not that unlikely - it really can happen. There's also the risk that you're likely to be on different electrical phases in different buildings which can also lead to fun and games.

    It's not a huge risk; as ever, there's a need to balance the cost of putting in the fibre against the risk of not doing so.

  15. Thanks to srochford from:

    CyberNerd (29th July 2009)

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    Geoff's Avatar
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    It's also illegal. See section B of the Building Regulations.

  17. 2 Thanks to Geoff:

    CyberNerd (29th July 2009), Oops_my_bad (29th July 2009)

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