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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