Maximum ethernet distance

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The distance most quoted for standard multi-twisted pair Cat cable is
100 meters.  I assume this is worst-case.

How much can this be streached?  Does it degrade in effective speed,
or does it just fail after a certain length?  Will it fall back to 10

I'd like to run about 650 ft, outdoors, rural, with some cable that
plugs into RJ45 at each end  without adaptors.  I don't need more than
3 Mbps.  What are my changes?


Re: Maximum ethernet distance

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Hi Phil. With a fiber mix, you can do 40km. Read this.
But don`t forget the lightning problem with your outside.

Re: Maximum ethernet distance

On Sat, 11 Nov 2006 16:29:40 GMT, wrote:

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You should assume that if you want to exceed that, you need
to put in a repeater or switch or whatever, instead of
trying to stretch it further.

If location is a problem to get power to the device, use PoE
adapters or PoE capable equipment.

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Yes, packets will be lost and resent at a certain length.

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Yes, it'll fail if extended further than the length at which
the packets can be resent.

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Some equipment might be able to fall back but in general you
choose to manually set it lower.

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I suggest using wifi and two directional antennas.

Re: Maximum ethernet distance

kony wrote:
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Just to point out, the spec on 10baseT is also 100 meters.

Re: Maximum ethernet distance wrote:
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Possible solutions:

1) Wireless solution

2) Free space optical (I had to mention this, because it is so cool).
    It seems the countries using this, can afford tall buildings, but
    cannot afford wires :-) /

3) Power line networking - if the outbuilding and the main building
    are powered from the same (North American) pole transformer, then
    perhaps this would work. You would still have the danger of
    lightning damage reducing these devices to ashes. This is the
    latest generation of technology, and is more adaptive than the
    older stuff. At the extreme distance you are planning on using,
    this might not work. Just had to mention this option for completeness,
    because you don't have to run any cables if the power lines are
    already there.

4) Fiber optic Ethernet. Cures the lightning danger problem. Years
    ago, the fiber I used to work with, cost ahout $1 per meter, but
    the price will depend on how the fiber is jacketed. I have no
    idea what a current price would be. Or how best to string
    or bury it.

5) Your CAT5 plan. (Lightning danger, even if buried.)
    10/100BT Ethernet has no ground. All four pairs of wires float.
    Lightning can induce voltage on a cable, even without hitting the

A web search presents conflicting information on the topic of 100BT

1) The length limit seems to be related to the Ethernet slot time. For
    100BT this is 5.12 microseconds (512 bit times, 10ns each for 100Mb/sec
    communication). This is to allow collision detection in "half-duplex"
    applications. (The 5.12 microseconds is the max time of flight, from
    one end of the cable to the other end, and then back again.) I don't
    see any references to what improvements can be expected with full duplex
    operation. If there was no Ethernet slot time/collision detection issue,
    then you would need info on what limits are imposed by attenuation and
    other cable effects.

2) This is a datasheet for an Ethernet PHY. The chip has adaptive equalization,
    which is a means of compensating for cable length. A register on the chip
    monitors the equalizer, and reads out what it thinks the cable length is,
    based on the degree of equalization needed. See page 41 and page 9. On
    page 9 it mentions "150 meters".

    This doc is slightly unrelated, but it does give a figure for the
    propagation speed of CAT5 cable (71% of the speed of light).

In view of the safety issues, I wouldn't spend any more time on
wired solutions. Something that doesn't use wires, is less likely
to burn something down or blow something up. Wireless technology
is a simple solution.

If you have radio spectrum to burn where you are located,
draft 802.11n is the latest wireless method. Apparently in
urban settings, 802.11n has had some impact on a neighbour's
wireless operation, so something like this is good in a
rural setting, as there may be fewer people to complain about
you messing up their Internet. But this might be overkill for
what you want.


Re: Maximum ethernet distance

The provebial 100 metres utp is per segment. If the connection performs
lowly or falls back to 10 Mbps, place a switch at, say 80 metres
distance, with incoming cable into the ordinary port and outgoing cable
in the uplink port. A switch is a repeater and separates collision
domains.Use good quality cables (cost more, naturally).
Paul wrote:
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Re: Maximum ethernet distance

  Some of the reasons for that distance limitation include delay time -
time for signal to travel to far end.  Generally, you need a media
converter for those distances.  Examples include:

  Also consider another problem.  Two computer connected by copper in
different buildings.  Then each building is the electrical equivalent
to a lightning rod connected to the other computer.  Therefore the
ethernet cable must enter each building adjacent to that building's
single point earthing electrode so that each of four (or eight) RJ45
wires is connected to that earthing electrode via a surge protector.

  Example of RJ45 protectors with necessary earthing connection
include: wrote:
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