Re: Bandwidth

From: Pascal Bourguignon (spam_at_mouse-potato.com)
Date: 09/29/05 

Date: Thu, 29 Sep 2005 23:40:27 +0200

gordonb.67fne@burditt.org (Gordon Burditt) writes:

>>This may not be exactly a unix question but I am implementing a project
>>in UNIX/C++. I could not find the group on which I can post the
>>message.
>>I am implementing a simulation that is supposed to have the bandwidth
>>of 9.6kbps. (The actual bandwidth is much more but I have supposed to
>>simulate the network at a bandwidth of 9.6kbps).
>>The distance between a particular set of nodes is 40 meters. From the
>>above information how do I calculate the time it takes for the packet
>>to go from one node to another node?
>
> The time from when you START sending the packet to the time when the
> recipient receives the whole packet is the transmission time of the
> packet (N bits / (9600bits/sec)) in seconds, plus the propagation
> delay. If it's async transmission over RS-232 you actually transmit
> 10 bits per byte, counting the start and stop bits.
>
> The speed-of-light propagation delay (133 nanoseconds) is negligible

The speed of light in materials is MUCH slower than in a vacuum.
http://www.livinginternet.com/i/ip_speed.htm

> compared to 1 character sent async (10 bits, including start and
> stop bits) = about 1 millisecond. The delay may be much more than
> the speed-of-light delay if there's anything in between, such as
> modulation/demodulation (modem), or a store-and-forward node (ethernet
> switch), or whatever.
>
> It is highly probable that a 40-meter straight-line cable will
> violate OSHA safety regulations by providing a trip hazard, so your
> cable may be much longer than 40 meters. The speed of electricity
> in twisted-pair or shielded cables is somewhat less than the speed
> of light in a vacuum.

Who said there was a 40 m cable between the two nodes? 

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
The world will now reboot.  don't bother saving your artefacts.

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