bandwidth question

[Jeffrey Watts]

On Wed, 10 May 2000, Jeff McCright wrote:

> I am not sure what you are asking, but Electricity travels at the
> speed of light, or so I'm told. As to the bandwidth, since the carrier
> signal of the fiber optic(light has a much smaller wavelength,

That's incorrect.  It's always a small fraction.  Remember, electricity is
the flow of electrons, and they are matter that have mass.  Light is a
bizarre particle-wave, and is energy.

Einstein tells us interesting things happen when you accelerate mass to
near c speed.  Electrons at near-light speed would do very interesting
things.  Can you say atom smasher?

> thus carry more data and because it is light, it is unaffected by
> crosstalk and other forms of RF interference.

But it is very susceptable to impurities and damage to the medium.  Not to
mention destructive interference.  Remember the wave behaviour of light?

> Thus you have Fiber that can allow more data to flow simultaneously
> with much less retransmissions of data allowing for greater or
> Bandwidth ("Speed"). Fiber will out perform Copper, period.

Bandwidth is capacity, not latency (speed).  Fiber has infinite capacity
(through dense wave division multiplexing).  Copper does not, since data
is transmitted through copper as a series of voltage lows and highs and it
needs the frequency of the shifts to be _much_ less than the speed of
light, assuming that you want to make networking equipment that doesn't
require a government-sized budget to purchase.

Also, your statement about retransmissions is misleading.  If you are
running Ethernet over fiber, you'll still have collisions assuming you are
using single-frequency fiber.  I also haven't seen any hard evidence that
states that fiber gives more reliable data transmission than adequately
shielded and properly installed coax or cat5.  Enlighten me if I'm
mistaken.

Fiber is used because it has near-c transmission speed (latency) and it
has much higher capacity (well, infinite).  Copper is used because it is
cheap to manufacture and manipulate and it is resilient to damage.

To answer the original question:

> so..if we setup a piece of fiber, and broke down all the packets (A
> and B) transmitted into two smaller units (A1, A2, B1, and B2) and
> then transmitted them alternating between packets A and packet B.
> (sending A1, then B1, A2, B2) which would essentially increase latency
> for each user, but at the same time, allow two users to transmit at
> the same time.

This is incorrect.  You are _not_ allowing transmission at the same time.  
You are allowing packets to be broken down into smaller packets, which are
then sent alternatively.  This will actually _decrease_ capacity (as you
are still sending the same amount of data down the wire, but you'll
require additional information in the little packets to recontruct them
into the bigger ones).  It would only increase latency in that the users'
machines would have to spend an extra step to recombine the
mini-packets.  This latency is not due, however, to the method of
transmission.  Light through fiber always travels at a fixed
speed.  Nothing you do (programmatically) can change that.

> appearing to run at the copper speed for both (2:1) essentially
> halfing the speed of fiber and doubling the bandwidth... in
> theory...would the overall network load be better (if the network
> segment were supporting a large user base) or would the result be a
> complicated network that would run at the same speed as the original?  
> note: im only speaking in theory, not practical..

Light over fiber is faster (higher latency) and has more capacity
(bandwidth) than electricity over a metal.  Period.  There currently are
fiber solutions that can transmit faster (NIC to NIC) and with more
capacity than any copper solution.  I'm sure there are also slower fiber
solutions than some copper ones.  But that is the speed of the _solution_,
NIC to NIC, not the capacity or potential speed of light over fiber.

So the answer is yes, the network load would be better on _any_ size user
base if you were using a fiber solution that was faster and had more
capacity than any copper solution available.

I kind of see what you were trying to get at, but you have to see that
your question answers itself -- it's basically saying "if a light-based
network is faster and has more capacity than copper, does a network based
on it have more capacity and more speed than a copper-based one?"

J.

o-----------------------------------o
| Jeffrey Watts                     |
| watts at jayhawks.net         o-----------------------------------------o
| Systems Programmer         | "Outside of the killings, Washington    |
| Network Systems Management |  has one of the lowest crime rates in   |
| Sprint Communications      |  the country."                          |
o----------------------------|  -- Mayor Marion Barry                  |
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