Re: Bandwidth

From: Gordon Burditt (gordonb.67fne_at_burditt.org)
Date: 09/29/05 

Date: Thu, 29 Sep 2005 19:56:21 -0000

>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
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.

                                                Gordon L. Burditt

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