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ethernet cat5e lenght 80m

Posted on 2016-11-25
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Last Modified: 2016-11-25
Dear experts,

I need to lay ethernet 5e cable in college building. The building has 10 floors and I need to lay 1 cable for each floor, because each floor is connected to specific Mikrotik router port.

The problem is that from 10th floor to server room is it about 80 to 100 meters. Each floor is limited to 17mbps, so I don't need higher speed.

Do you have some real experience or a link to some trusted info about it?


Regards,
Jarda
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Question by:JardaCZ
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Expert Comment

by:Antzs
ID: 41901268
The longer the cable does not actually relate to the speed in which data travels.  The max 100m Ethernet cable length is just a TIA standard.  For any cable longer than 100m an active device is required in between the cables to boost up the signal to prevent signal drops.

But, I have used cable longer than 100m, in my environment( I think it was 250-300m) and it worked just fine.  That said, I still prefer to follow the recommended standard unless the situation does not gives you the choice to follow the standard.
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Assisted Solution

by:Dr. Klahn
Dr. Klahn earned 125 total points
ID: 41901279
Considering that the demand for bandwidth is at least doubling every decade, I'd pull at least two fibers in addition to the copper.  In less than ten years you'll need it.  It's less expensive over the long run to pull it now than to go back later and pay for another pull.
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Assisted Solution

by:John Tsioumpris
John Tsioumpris earned 125 total points
ID: 41901419
You also have 2 other options
1. Move the router to an inbetween floor ...e.g. 4th so the lengths of the cable are considerable shorter
2 Use CAT6 cable that is rated for 100m...
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Accepted Solution

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Predrag Jovic earned 250 total points
ID: 41901423
But, I have used cable longer than 100m, in my environment( I think it was 250-300m) and it worked just fine.
No way with copper!
:)
Typically copper cable work up to 125 and also speed typically is 10Mb in that case. Signal is so degraded that 100Mb is impossible.
(There are also other reasons why cable should not be longer).

I agree with Dr. Klahn. Buy better Quality cables (cat 6a or higher) to be future proof. Always place multimode fiber between buildings if budget allows it.
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Author Comment

by:JardaCZ
ID: 41901462
So I will pull Datacom Cat5e cable and will see what happen. In the worst case I will later buy some cheap switch and put it somewhere between.

There is about 20 devices on each floor, 2 buildings with 10 floors each. About 400 active devices (students) shares 300mbps internet connectivity. As a router, I used 24 port Mikrotik for $160. Poor students... But the budget is not so high.

Do you agree with this solution or I will beat my head against the wall in few days?


Kind regards,
Jarda
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Expert Comment

by:Predrag Jovic
ID: 41901478
I typed answer for cables only. For design consideration more details should be provided (including basic topology and list of devices in use).

But from what I read, why wait for few days? Start beat your head against the wall right now.
😊

For start place 2 fibers between buildings (if not already present), at least that's what I would do (Dr.Klahn also suggested it).
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Author Comment

by:JardaCZ
ID: 41901536
Those buildings are very close together (20 meters). They will not pay fibers or some sophisticated solution, there is no budget for it.

Now there is one router, one cable to each building. On a 1st floor is 100mbps switch, from this switch it's connected to another switch on 2nd floor and so on. Simple cascade of 10 switches in each building. When one switch fails, the rest of building doesn't work.

Should I spend $1000 for a "small upgrade" described above or let it as is.


Thanks,
Jarda
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Author Closing Comment

by:JardaCZ
ID: 41901617
Thanks a lot for help!
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Expert Comment

by:Predrag Jovic
ID: 41901626
You know limitations, those are just best practice sugestions.
Typical design is L3 switch per building.

Where you will most likely have problem is natting for 400 hosts (but again don't know complete design). NAT uses router's CPU for work and is not offloaded to a ASIC. So that can become a huge problem, since it can effectively kill your router.
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