Re: [ns] delay of LAN

[Brian Lee Bowers <bowersb@lanl.gov>]

On Thursday 26 July 2001 12:05, Gary Leung wrote:
> Hi seniors,
>
> I have cnstructed 2 LANs connect with a duplex link as following:
>
> node 0 ------node 1======node 2--------node3
>
> node 0 and node 1 belong to LAN 1 while node 2 and node 3 belong to
> LAN2.
> These twon LANs are connected with a duplex link. I have set the
> delay as 1ms when cnstructing a LAN and the delay of the duplex
> link 1ms as well. the bandwidth of both LAN and the duplex link are
> 10Mb. What is the delay the packets will travelled from node 0 to
> node 3?

Since I can't give a "number" answer that is always correct, I'll 
lead you through the general calculations.  At the end of the e-mail, 
I'll give answers for two specific packet sizes.

How long does it take for a bit to get from node 0 to node 1 (the 
link delay)?  How long from node 1 to node 2?  How long from node 2 
to node 3?

The sum of those three times is the partial answer.  You must also 
consider how long it takes for a packet to be injected into the 
network.  If the link can carry 10Mbps, how long (in seconds) does it 
take for a bit to completely pass any given point in the network?  
How long will it take to inject a full packet into the network?
	(bytes per packet * bits per byte) / bits per second

My calculations say it should take 6.6 ms for a packet of 1500 bytes 
to travel from node 1 to node 3 (from transmission start to 
transmission complete) barring any interfering behavior.  A 40 byte 
packet should only take 3.096 ms to travel the same path.

-- 
Brian Lee Bowers	|	RADIANT Team (Summer Intern)
bowersb@lanl.gov	|	Los Alamos National Laboratory