>From: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>Reply-To: Priscilla Oppenheimer <[EMAIL PROTECTED]>
>To: "Brian Lodwick" <[EMAIL PROTECTED]>, [EMAIL PROTECTED]
>Subject: Re: EASY ?? FOR MOST OF YOU
>Date: Tue, 23 Jan 2001 11:56:25 -0800
>
>At 02:33 PM 1/23/01, Brian Lodwick wrote:
> > 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
>
>Hi Brian,
>
>I hope our conversation isn't like the reserved token on FDDI and we're the
>only ones still listening! &;-)
>
>If the IEEE had just been changing the physical diameter, a factor of 10
>would have made more sense (especially since wiring specifications are
>often in metric). Since they were also changing the number of bits that the
>MAC sends, they probably wanted that to be in octets. (That is just a
>guess! &;-)
>
>Here's another question. How badly did they affect efficiency by
>"enhancing" the CSMA/CD this way?
I found something that showed percentages
>Does a receiver throw out a frame if the collision happened in the carrier
>extension part even though the actual data part arrived without error?
>(Yes! It has to because the sender is going to resend and Ethernet can't
>deal with duplicate frames.)
>
>And how about all that overhead for small frames? Let's say the next layer
>up sends a 512-bit frame. That ends up being a 4096-bit frame with a 64-bit
>preamble and 96-bit interframe gap.
>
>Consider an application that is trying to output a bunch of small frames at
>a quick rate. If it has to add a bunch of bits to reach 4096, will it be
>able to send at the proper rate? When it's done and releases control, some
>other application will probably jump in, and the poor small-frame
>application has to try to get control again.
>
>Well, they addressed this also. The IEEE standard lets a sender send
>multiple frames! According to Rich Seifert in his "Gigabit Ethernet" book,
>a station may choose to burst frames if there is a frame in its transmit
>queue when it has finished sending its first frame plus extension (if
>necessary). It does this without contending again for use of the channel.
>During the interframe gap it sends non-data symbols and then sends its next
>frame.
An optional feature called frame bursting which sounds like a cool deal to
me, too. I would guess you would just have to be one with your data and set
this if you need it.
>
>But is that fair to other senders? Well, was Ethernet ever fair?
Was Source-routing ever fair either? Fair usually requires CPU and slows
things down.
>It was fair from an access point of view, but senders of big frames could
>use a
>greater portion of the bandwidth. This new bursting feature makes it fair
>from a bandwidth usage point of view. A station can send for up to a
>burstLength time (plus one frame) regardless of whether the frames are
>short or long. This is a major difference. It's like custom queuing versus
>priority queuing.
>
>I'm beginning to think that Gigabit Ethernet is best deployed on a
>full-duplex (not shared) link.
Howard Frazier agree's with you too, but things may change and maybe
everyone will have a gigabit NIC on their machine in a couple years from
now.
>I get squeamish when I hear about all these
>changes to the CSMA/CD that we have known and loved for so long. &;-)
So does the 802 committee. It would seem to me that Fast Ethernet is fast
enough for half-duplex applications, and gigabit would be nice as just a
full-duplex protocol for between routers, switches and servers, and go ahead
and get rid of CSMA/CD, but that wouldn't be thinking ahead, and that
wouldn't really be ethernet anymore would it?
>Priscilla
>
>
>
> > >>>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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>[EMAIL PROTECTED]
> > >>
> > >>_________________________________________________________________
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> > >>
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> > >
> > >
> > >________________________
> > >
> > >Priscilla Oppenheimer
> > >http://www.priscilla.com
> > >
> >
> >_________________________________________________________________
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> >
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>
>
>________________________
>
>Priscilla Oppenheimer
>http://www.priscilla.com
>
>_________________________________
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>Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
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