"Jeff Liebermann" <jeffl@comix.santa-cruz.ca.us> wrote in message
news:3fddp3dj87ee797n9dethg08oebbdn1ini@4ax.com...
> On Tue, 22 Jan 2008 22:24:29 -0500, "Bill Kearney"
> <wkearney99@hotmail.com> wrote:
>
> >> The spec actually states 100 meters being the max length which is 328
> >> feet, this includes all patch cables.
> >
> >Indeed. I've had runs slightly longer that worked, and ones shorter that
> >didn't. There are enough variables to make it reasonable to think of it
as
> >a 300' limit.
>
> Nope. One of my fun demos is to take a 1000ft roll of CAT5, crimp
> connectors at both ends, and connect it between my laptop and a Cisco
> 1900 managed switch. It won't do 100mbits/sec (100baseTX) in either
> HDX or FDX, but will certainly do 10mbits/sec (10baseT) in either HDX
> or FDX. The trick is to force the connection to 10mbits/sec and don't
> let NWAY try to set it to 100mbits/sec. SNMP from the switch and
> netstat shows no transmission errors. Thruput is also at wire speed
> with FDX.
>
> >My point wasn't to quibble over the total limit, but to
> >stress that the distance needs to include ALL portions of the connection.
> >To the wall, up and over the ceiling, etc. If the other build is really
> >only 200' away then he's got plenty of distance to play with inside the
> >buildings.
>
> Yep. You're also correct about the extra cable for bends and turns.
> I've gone over 300ft several times by forgetting about such details.
>
> Note that the 100meter limit is between switches.
one of the wiring standards for putting Cat5 into buildings puts this as 90m
for the fixed wiring, and 10m for 2 patch leads (1 each end). AFAIR this was
for that wiring system rather than the 100 Base-Tx standard.
You can add as many
> ethernet switches as needed along the line to deal with regenerating
> the signal. I've done 1500ft that way with 3 switches between
> endpoints. I think that's about the limit as it was a bit flakey when
> the switches got hot. I think (not sure) that the limit is set by the
> end to end latency (delay), which causes ACK timing problems.
not really. dealy thru a modern switch hardware is a few 10s of uSec.
Then you have added a store and forward delay (in each direction)
- but a 1500 byte packet is 12k bits, so even at 10 Mbps that is 1.2 mSec -
say 2 mSec at 10M, and 200 - 300 uSec at 100M
ACK timers at the IP and above layers are Sec or more so are not going to
care, and there arent any L2 ones in Ethernet (unlike wireless).
FWIW Ethernet bridging over SDH is now fairly common in telco networks -
these have a bridge each end and then adapt the bits from the Ethernet
frames to run across 1 or more VC-x "pipes" inside the SDH cloud.
They work fine over 100s of Km, so a few hops over Cat5 or local fibre are
not going to be a problem.
Maybe you need better switches?
>
> >Two reasons I refuse to use ethernet wire buried: lightning and voltage
> >transients. If only because I've had personal experience with both
wrecking
> >equipment.
>
> Sigh. We don't get much lightning in California, but the few
> lightning bolts that hit a local tower managed to blow up most of my
> media converters. Fiber works much better.
Agreed. And the "fault caused by a hit can be spectactular.
We had a wall mounted Cisco router took a hit on an overhead cable carrying
its ISDN line (which was "surge protected).
The smoke marks were 2 or 3 feet long, and most of the innards had very
briefly been molten.....
So - a significant fire risk as well if your area is exposed to this risk -
and as lightning is classed as "act of god" might be a problem with
insurance...
>
> >Not as expensive as the hassle of replacing fried equipment.
Yes - if you have external maintenance, the cost of an engineer visit is
probably more than that of a router or switch.
And - act of god again, so it may all be chargeable......
>
> The equipment is fairly cheap. My time to drive up to some mountain
> top, with the wind blowing, rain falling, and lightning zapping, is
> considerably more expensive. In retrospect, I should charge hazzard
> or combat pay. However, if you wanna do gigabit fiber, the media
> converters are VERY expensive. It's often easier to settle for
> 100mbits/sec and save your dollars until the prices drop.
>
> --
> # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
> # 831-336-2558 jeffl@comix.santa-cruz.ca.us
> # http://802.11junk.com jeffl@cruzio.com
> # http://www.LearnByDestroying.com AE6KS
--
Regards
stephen_hope@xyzworld.com - replace xyz with ntl