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Posted by James Knott on February 19, 2005, 2:25 pm
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Skybuck Flying wrote:
> I am kinda surprised that it's not a whole number. I was excepting a whole
> number for maximum efficiency :D
>
> Am I missing something ? maybe extra overhead bits ?
Why would it be a whole number? There was no intended relationship between
packet size and bit rate. Try using your argument on the size of cars that
can travel on a highway, to see if it stands up.
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Posted by Walter Roberson on February 19, 2005, 8:25 pm
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:I am trying to figure out how many maximum sized packets can be
:sent/received over 10 megabit ethernet per second in theory (or ideal
:circumstances :D)
:They say 10 megabit ethernet runs at exactly 10.000.000 bits per second. (?)
That's the first mistake. Any ethernet implimentation you are likely
to encounter runs asynchronous, no synchronous. 1E7 is the -maximum-
data rate, which will never be achieved in practice. Especially at
10 megabit ethernet, if no station has anything to send, then the
line is quiet. When a station has something to send and the line
has been quiet for at least the inter-frame gap, then the station
just starts sending, rather than waiting to synchronize with a
clock.
Synchronous ethernet is a lot harder, because you have to synchronize
the bit edges of all the stations on the segment, even though there
are different propogation delays due to distance, and even though
there may be repeaters along the way.
:1.250.000 bytes / 1538 bytes = 812,74382314694408322496749024707
:I am kinda surprised that it's not a whole number.
Then you will be even more surprised when you look at 100 megabit
per second or gigabit speeds, which send multiple bits per symbol
and which have error correction built in. 100 Mbps for example sends
in chunks of 4 bits of data, encoded as 5 bits.
:I was excepting a whole
:number for maximum efficiency :D
That statement presumes that all of the systems are running with
the same clock (to within a fraction of a bit time) and that there
is something special about 1 second boundaries. Once you give up
on sychronizing the systems together then you can see that the
data keeps running, and that expecting a whole number of packets per
second is about as useful as expecting that on a car that is driving
at 100 kilometers per hour, that each wheel will make a whole number
of revolutions per second.
--
Live it up, rip it up, why so lazy?
Give it out, dish it out, let's go crazy, yeah!
-- Supertramp (The USENET Song)
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Posted by James Knott on February 19, 2005, 3:43 pm
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Walter Roberson wrote:
> That's the first mistake. Any ethernet implimentation you are likely
> to encounter runs asynchronous, no synchronous.
The packets are asynchronous, but the data within a packet is synchronous.
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