-----Original Message-----
From: Julio Arruda [mailto:[EMAIL PROTECTED]]
Sent: Segunda-feira, 5 de Junho de 2000 11:23
To: Lista de Discuss�o Rede Wan
Subject: RE: [redewan] Capacidade real FastEthernet
Lista de Discuss�o Rede Wan - http://www.networkdesigners.com.br
O maximo que "cabe" no meio fisico seria 100 Mbps, certo ?
Porem, cada pacote tem um "overhead", de preambulo antes do pacote, e de "interframe gap", depois do pacote.
Estes "pedacos de banda mortos" sao expressos em "bit times", portanto o preambulo na geracao de pacote seria de 64 bits, e apos o recebimento, vao existir 96 bits de intervalo antes do proximo (em todos os equipamentos seguindo as normas).
Estes 160 bits mortos por pacote sao "perdidos" em cada pacote, seja um pacote minimo (64 bytes == 512 bits), seja no maximo (atualmente 1522, creio que contando com o tag IEEE 802.1Q).
Em gigabit "half-duplex", o negocio complica, mas como nunca vi um repetidor gigabit, pode ignorar..:-)
[], <O-O>
-----Original Message-----
From:�� Roberto Bras [SMTP:[EMAIL PROTECTED]]
Sent:�� Friday, June 02, 2000 5:02 PM
To:���� Lista de Discusso Rede Wan
Subject:������� RE: [redewan] Capacidade real FastEthernet
Lista de Discuss�o Rede Wan - <http://www.networkdesigners.com.br>
Julio,
�
Me desculpe, mas n�o entendi NADA do que vc disse. D� para detalhar/explicar um pouco mais?
�
[],
Br�s.
�
-----Original Message-----
From: Julio Arruda [ <mailto:[EMAIL PROTECTED]>]
Sent: Quinta-feira, 25 de Maio de 2000 13:31
To: Lista de Discuss�o Rede Wan
Subject: RE: [redewan] Capacidade real FastEthernet
Lista de Discuss�o Rede Wan - <http://www.networkdesigners.com.br>
Se nao me engano, o maximo teorico seria:
100Mbps - "tempos mortos"
Fazendo um cut&paste descarado de um post recente na comp.dcom.lans.ethernet (note que os "timings" de giga/fast/ethernet sao iguais em "bit times", e como nao estamos levando em conta em giga-half-duplex o "quebra-galho" chamado carrier extension, da para usar o mesmo "conceito).
[], <O-O>
===========================
n article <[EMAIL PROTECTED]>,
Sam� <[EMAIL PROTECTED]> wrote:
>Hi,
>
>May we expect more than 500 or 600 Mbps on an Ethernet Gigabit
>link ?
You may expect well over 900Mbps in each direction on a Gigabit Ethernet
link. That is, of course, assuming that you have the traffic to fill it.
>What is the general rule for Ethernet saturation and does it
>depend on the medium that is being used (fiber, copper, ...) ?
Ethernet in full duplex mode can be as saturated as a serial line between
two points.� Depending on frame size Upper-layer protocols will limit the
amount of traffic that can pass in any one conversation as the protocols
wait for acknowledgements.� The one caveat is that there is a 160 bit-time
gap between packets for historical reasons (96 bit interframe gap, 64 bit
preamble).� So, for a 1524 byte frame, Ethernet is only 98.7% efficient.
For 64 byte frames, Ethernet is only 76% efficient.� Average traffic is
256 bytes, which is 92.7% efficient.
Ethernet in Half duplex can be saturated to the same amount, However, the
contention mechanism deployed to determine what happens when two devices
attempt to communicate at the same time (collisions) will offset the
efficiency to some extent.� A single collision on a 1524 byte frame will
knock your efficiency down to 97.4%, while on a 64 byte frame it will be
61%.
So, on shared 10 megabit ethernet with only 64 bytes frames, and a 100%
collision rate, you should end up with 6.1 Mbps.� With 1500 byte frames
and 100% collision rate, you should end up with 9.74Mbps.� Not too shabby
that...
--
Daniel J McDonald CCIE # 2495, CNX
[EMAIL PROTECTED]
I support Alan Keyes for President - < <Http://www.keyes2000.org>>
Visit my website: < <http://www.io.com/~djmcdona>>
(nao entrado em detalhes de cpu para segurar o rojao).
[], <O-O>
-----Original Message-----
From:�� Alessandro R Nobre [SMTP:[EMAIL PROTECTED]]
Sent:�� Tuesday, May 23, 2000 4:26 PM
To:���� Lista de Discusso Rede Wan
Subject:������� [redewan] Capacidade real FastEthernet
Lista de Discuss�o Rede Wan - < <http://www.networkdesigners.com.br>>
Pessoal,
�
Alguem saberia me dizer qual a capacidade de transmissao de uma rede Fast Ethernet. E se utilizo Full duplex como ficaria esta capacidade real ?
�
[]�s
�
********************************************************
Alessandro R Nobre
[EMAIL PROTECTED] < < <mailto:[EMAIL PROTECTED]>>>� |� ICQ: 70701329
********************************************************
� _____�
�<< File: Alessandro R Nobre.vcf >>
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