my 2 Brian's worth, I"m just a little bored and wanted to add my definition
and additional notes to your analogy below.
>>>Brian
>From: "Tony van Ree" <[EMAIL PROTECTED]>
>Reply-To: "Tony van Ree" <[EMAIL PROTECTED]>
>To: "Priscilla Oppenheimer" <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
>Subject: RE: EASY ?? FOR MOST OF YOU
>Date: Wed, 24 Jan 2001 09:10:54 +1100
>
>Hi,
>
>I just glance at some of the discussion. Here is my two bob's worth. It
>is fine to sit there and say how long it takes a signal to get from one end
>of a cable to another. In the purest thoery both ends happen
>simultaneously (we all know this is not true it is on copper about 75% of
>the speed of light in fibre 90%) That is one argument and this would have
>one believe that one could therefore send 10Meg further than 100Meg full
>duplex further than half. (and to a limited degree you could)
>
>We can only have one signal on one wire at one time for various reasons
>(probably not true but it is for the theoretical purpose)
>Ok, what happens when we put a pulse on a line. In a nutshell it is not
>all to dissimilar to putting water onto a plate. The bigger the plate the
>longer it takes to fill. Therefore the longer the cable the longer it will
>take the remote end to see the signal reach the full strength.
>(Attenuation)
***
Attenuation I would say is the degradation of the original signal due to
external forces such as absorption (Electricro-magnetic energy turned into
heat energy), spreading (amplitude decreased due to physical distance
propagation -Cylindrical, Spherical, and Dipolar), and scattering (Amplitude
decreased due to physical impurities in the physical medium). Repeaters
would completely fix the attenuation problem if there were no outside forces
causing ambient noise.
>As anyone with tinitus will tell you it is hard to hear in a crowded room.
>So it is with cable (Cross Talk) the longer the cable the more chance of
>crosstalk.
***
I love the analogy. I studied Acoustics and I would like to add my own
analogy if I can:
Lets say you are in a long tunnel and your friend at the other end makes a
really low frequency noise in his/her message to you. Instead of the sound
reflecting off of the walls of the tunnel and bouncing on down to you it
decides it's frequency is too big for the tunnel diameter and it refracts
out of the tunnel, and the guy in the tunnel next to yours couldn't hear
what his partner was saying because that low frequency sound your friend
sent (that got refracted out of your tunnel) got into his tunnel and mucked
up his message.
-Crosstalk would be more prevalent in a shorter straight strung cable than a
longer cable with twisted pairs.
>I think you will find at 100 Metres there is a good balance of all these
>things and therefore the limit. To get further we could overcome
>attenuation by sending stronger. This would increase crosstalk to
>neighbours. Better balancing might work but this would be costly.
>I feel someone has thought about a lot of this.
>
>Just some thoughts and my way of viewing cable lengths,
>
>Teunis
>Hobart, Tasmania
>Australia
>
>
>On Tuesday, January 23, 2001 at 12:54:11 PM, Priscilla Oppenheimer wrote:
>
> > At 03:27 PM 1/23/01, Erik Mintz wrote:
> > >I have a question regarding CSMA/CD vs full duplex. If the problems
> > >relating to distance are set due to the limitations of CSMA/CD,
> > >what are the limits when using full duplex?
> > >I have had several situations where I had to run fiber because of
> > >distance, but these
> > >where almost invariably full duplex uplinks or trunks. Can I go farther
> > >with copper if the link is full-duplex?
> >
> > A copper 100-Mbps full-duplex DTE-DTE link is still limited to 100
>meters.
> > Gigabit Ethernet has a 25-meter standard for use with STP, and work on a
> > 100-meter segment for use with UTP is underway, last I heard.
> >
> > I think the 100 meter rule is based on attenuation. Note that the
>EIA/TIA
> > also says you shouldn't have more than 100 meters for your horizontal
> > cabling from a wiring closet to a workstation. (90 meters actually, plus
>a
> > 10-meter patch cable.) I'm sure the rules are related to each other and
>are
> > probably to avoid too much attenuation. I'm not a physical-layer person,
> > though. Someone else can probably provide a more authoritative answer.
> >
> > Priscilla
> >
> >
> > >-Erik
> > >
> > >-----Original Message-----
> > >From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of
> > >Priscilla Oppenheimer
> > >Sent: Monday, January 22, 2001 7:16 PM
> > >To: Brian Lodwick; [EMAIL PROTECTED]; [EMAIL PROTECTED]
> > >Subject: Re: EASY ?? FOR MOST OF YOU
> > >
> > >
> > >At 09:20 PM 1/22/01, Brian Lodwick wrote:
> > > >BBBBBBBBBBBBBBBBBBBBBBBBBBBBB for
> > > >
> > > > >>>Brian
> > > >My additional question on top of this one is:
> > > >
> > > >If the maximum legal length was set to 1/10th the size to make
>regular
> > > >(10Mb/sec) increased by a factor of 10, what was done to further
>increase
> > > >100Mb/sec Ethernet by a factor of 10 to get Gigabit Ethernet?
> > >
> > >I like your plan to turn this into a non-easy question! The only
>experience
> > >I have with Gigabit Ethernet is in a fully-switched network where every
> > >port is full duplex, in which case CSMA/CD parameters are not an issue.
> > >However, shared, half-duplex Gigabit Ethernet is viable also.
> > >
> > >With shared 10 and 100-Mbps Ethernet, the minimum frame size is equal
>to
> > >the maximum round-trip propagation delay of the network. In other
>words,
> > >the minimum frame size is equal to the slotTime = 512 bits. Sticking to
> > >this rule would haver resulted in impracticably small networks for
>Gigabit
> > >Ethernet, however. The solution was a process called "carrier
>extension."
> > >
> > >According to Rich Seifert in his excellent book, "Gigabit Ethernet,"
>"The
> > >key change is that the slotTime and the minimum frame are no longer the
> > >same. The minimum frame is maintained at 512 bits (64 bytes, as in 10
>Mbps
> > >and 100 Mbps Ethernets), but the slotTime is set at 4096 bit-times (512
> > >bytes).
> > >
> > >Frames that are shorter than the slotTime are artificially extended by
> > >appending a carrier-extension field so that they are exactly one
>slotTime
> > >long. This extends the duration of the time that the station
>transmits....
> > >If a collision occurs during any time from the beginning of the frame
>to
> > >the end of the extension field, the MAC will jam, abort, and backoff."
> > >
> > >See the book for even more gory details! &;-)
> > >
> > >Priscilla
> > >
> > >
> > >
> > > > >>>Brian
> > > >
> > > >
> > > >attenuation is effected by 3 elements spreading, scattering, and
>absorption.
> > > >
> > > > >From: Alvarado Jesus <[EMAIL PROTECTED]>
> > > > >Reply-To: Alvarado Jesus <[EMAIL PROTECTED]>
> > > > >To: "'[EMAIL PROTECTED]'" <[EMAIL PROTECTED]>
> > > > >Subject: EASY ?? FOR MOST OF YOU
> > > > >Date: Mon, 22 Jan 2001 14:10:43 -0500
> > > > >
> > > > >The network span of a 100Base-T Network (205) meters is approx. 10
>times
> > > > >smaller than the network span of a 10Base-T network (2500) meters
>Because
> > > > >....
> > > > >
> > > > >A) , Higher speed data signals attenuate more quickly and so
>cannot be
> > > > >transmitted that far
> > > > >
> > > > >
> > > > >B) . Both Networks have minimum frame sizes of 64 bytes and the
>network
> > > > >spans must be tied directly to the minimum frame transmission time
>to
> > > avoid
> > > > >collisions.
> > > > >
> >
> >
> > ________________________
> >
> > Priscilla Oppenheimer
> > http://www.priscilla.com
> >
> > _________________________________
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> >
>
>
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