Group,
I will go ahead and post the answer to this question. I believe your
answer Priscilla is absolutely correct.
My resources are Interconnections book (for a general understanding), but
mostly from a couple of *IEEE articles authored by Howard M. Frazier, Jr.
and a free book I got on Gigabit Ethernet I got from Cisco.
Well it actually seems everything isn't written in stone yet, but it looks
like the 802 committee held onto CSMA/CD which is the portion of the
protocol I was referring to in my question -802.3z(although there is a
version created which takes advantage of full-duplex contention-free
environment and doesn't use carrier detection. Quoted from the IEEE document
Howard M. Frazier, Jr. writes "In the early phases of deployment, Gigabit
Ethernet will be used to interconnect high performance switches, routers,
and servers in LAN backbones. The full-duplex operating mode is very well
suited to this application environment, and will typically be favored over
the CSMA/CD mode.")
So back to the question, as you mentioned Priscilla to allow the CSMA/CD to
accurately detect a collision and backoff in time, when the counters tick 10
times faster, they have extended the minimum frame size and will append
stuff (carrier extension) on the tail end of the regular Ethernet packet to
get it up to 512 bytes. (I think this is kindof neat since with this carrier
extension, compatibility between different LAN types and Gigabit should be
rather easily implemented, a bridge can just rip this extension off and
treat it as a regular ethernet frame. Of course old bridges/switches will
need software upgrades to be able to recognize this extension)
I think the only question that is left unanswered is, if anyone bothered
to do the math, why does the minimum frame size only increase by a multiple
of 8 and not 10?
512 / 64 = 8
>>>Brian
* IEEE article can be found at: http://computer.org/Internet/v1n5/ether.htm
>From: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>To: "Brian Lodwick" <[EMAIL PROTECTED]>,[EMAIL PROTECTED],
>[EMAIL PROTECTED]
>Subject: Re: EASY ?? FOR MOST OF YOU
>Date: Mon, 22 Jan 2001 16:15:31 -0800
>
>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.
>> >
>> >_________________________________
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>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>
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