Re: Bandwidth

From: Pascal Bourguignon (spam_at_mouse-potato.com)
Date: 09/30/05 

Date: Fri, 30 Sep 2005 15:33:04 +0200

"rishi.shah@patni.com" <rishi.shah@patni.com> writes:

> I may have created some confusion by my expalnation early on.
> Here are the specifications more clearly
> I am implementing the project in unix/c++ and each node represents a
> process on a separate machine.
> They communicte using TCP sockets
> Each node has a configuration file that has the location co-ordinates.
> When I said 40m distance, I meant the euclidean distance between two
> nodes is 40m.

Which is a useless data.

For example, when I communicate with my customer that's at 10 km, if
there was a direct earth cable between us, it would take 20 km because
there's a sea between us, and in actuality, it takes more like 1600
km, because the internet is not as meshed as its propaganda let you
believe, it's really a hierarchical star topology, and that, that
we've got the same ISP, our packets still traverse forth and back the
country.

If you restrict yourself to LAN, nowaday ethernet is a star topology
too, with a central HUB. The distance between the nodes doesn't matter
what matters is the length of the cables.

> I have the formula
> Latency = Propagation time + Transmit time + Queing time
> where Propagation time = Distance / Speed of light = m/ (m/s) = seconds
> and Transmit time = Packet size/ Bandwidth = bits / (bits/s) = seconds
>
> I assumed that the Propagation time = 0 since the distance is
> negligible as compared to speed of light.

We don't have enough data to say so.

> Now is my assumption of packets travelling on a TCP socket as fast as
> light incorrect?

This is meaningless! Think about what you're writing!

> Since this project is a simulation I am not aware of the actual
> material between the nodes.

You can parametrize it, and look up technical data on the web.

> Queing time I have assumed to be zero since it is my own simulation.
> In such a case is the formula Latency = Packet Size/Bandwidth. Am I
> Correct?

With some assumptions.

> If I wnat to consider the tranmission time do I have first find the
> material and then the speed of travelling in that material. Am I
> Correct?

Yes. 

-- 
__Pascal Bourguignon__                     http://www.informatimago.com/
Grace personified,
I leap into the window.
I meant to do that.