Could someone please help me with a fast ethernet problem I am having. We
have a POP in a 27 floor building, and have a rj45 run from the the bottom
of the building (in the telco room) to the top of the building. We have
cisco switches on either end and we are seeing about 5-20% packet loss on
the trunk.
Are we running into a distance limitation of fast ethernet, or are we suffering
from another problem? I read that 328 feet is the limitation of fast
ethernet. Is there anything short of getting a repeater for the cable run
that I can do to boost the signal?
What type medium are you using? If it is normal Cat5/6 then the
limitation is 100 meters for total distance and as you approach that
limit the signal degrades. That said, 100baseFX can run for 400 meters
due to the fact that it is fiber, both are part of the fast Ethernet
specification though. A repeater would boost signal, but perhaps a
switch in there might not be a bad idea, segment the 27 floors into
VLANs, reduce overall traffic traveling between floors and eliminate the
27 floor run.
I used to see these exact same results when I would setup Wireless pop's on
towers taller than 400Ft. I was able to push the envelope a bit, however
when I saw the issues that you speak of, it was when I had bad crimps, or
sometimes a bad cable all together. Cat5 should be fine for this... if you
figure 12ft risers you are probably cutting it close on the distance but not
going over it.
Well, when I don't have drawings or prints, I usually figure on 12 or 13ft
per floor. So, figure somewhere between 324 and 351 feet from 1st floor
to the ceiling on 27. For a run like this, you probably wanted to use fiber
with media converters on each end. (Assuming you're not running
switches with 100BaseFX ports or a GBIC slot...)
you need to put a fluke lanmeter or similar device (with tdr) to validate
the cable... you may just need to reterminate the ends, but it's also
likely that it's simply way out of spec.
Indeed altho depending on purpose bear in mind a repeater is just a hub or
switch, if you can fit one half way up you should solve your loss problems.
Yeah 328 is the alleged limit but it can go further usually, as another reader
said you need good connectors and cables tho. A more likely cause of trouble
for you in the ducting is interference if you're running alongside AC mains and
other data cables both of which will increase noise and reduce the limit even
more.
I believe your pushing the limits as to ethernet over Cat5.
I can suggest you use the very best cable (shielded of course) you can get, and be meticulous in your connector installations and you might get away with it. Avoid other wiring if possible (fat chance huh?) and anything electrical interference producing, like fluoro ballasts, transformers etc. etc.
Ground the end closest to earth ground to a good common point ground in the building, (not a power box) and leave the other end free floating and not touching anything electrically.
100 meters is supposedly the limit for ethernet, and "assuming" a 12' floor, your'e around 24 feet over spec.
You might try to find some cat 6 cable if you can, its supposedly super premium cat 5, with better freq response and jittter control. http://www.controlcable.com/products/category_6_cable.html
One last advice, use REAL good patch cables as well...they may help squeeze the last bit of performance out..
Steve,
What type medium are you using? If it is normal Cat5/6 then the
limitation is 100 meters for total distance and as you approach that
limit the signal degrades. That said, 100baseFX can run for 400 meters
due to the fact that it is fiber, both are part of the fast Ethernet
specification though.
And just for the record, 100BaseFX in full-duplex mode can actually run for
2000 meters
with multimode fiber 62.5 micron core, 125 micron outer.
100 meters is primarily a "timing limit" for half duplex, ie if you're
running half duplex, how large can your broadcast domain be before you
risk losing small packets due to the collission not reaching all speakers
on the wire (and this counting the max number of repeaters in a broadcast
domain). 100/half will do padding of small packets to achieve just this
effect.
I've seen 170meter CAT5 100 meg full duplex links working just fine. Of
course, as stated before, it's an interference thing, if you have a lot of
noise around the wiring you'll shorten the usable length.
Of course, this is a ethernet chipset issue, but there are definately
chipsets out there capable of electronically driving links much more than
100 meters just fine.