I'm no expert but the explanation from the book Cisco LAN Switching chapter 1 page
11-12 seems logical to me.
Jojo
-----Original Message-----
From: Tony van Ree [SMTP:[EMAIL PROTECTED]]
Sent: Wed, January 24, 2001 1:11 AM
To: Priscilla Oppenheimer; [EMAIL PROTECTED]
Subject: RE: EASY ?? FOR MOST OF YOU
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)
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 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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