Re: ns evaluation

[Kedarnath Poduri <kpoduri@BayNetworks.COM>]

At 04:52 PM 6/18/98 -0400, Huseyin Cenk Ozmutlu wrote:
>Hello everyone,
>
>My name is Huseyin Cenk Ozmutlu. Curretly, I working on a project
>involving network simulation. We are evaluating different simulation
>packages and ns is one of the packages. I went over the ns-users mailing
>list but I couldn't find satisfactory answers to my questions which are
>presented below. We will present our results at july 1st, therefore I
>would appreciate any response. 
>
>My questions are:
>
>1- Is it possible to create different size packets according to a
>probability distribution everytime a packet is generated during a FTP or
>Telnet connection? 
>
>2- Is it possible arrange random interarrival times between packets
>generated? I know it is done in Source/Telnet object, but how about in
>FTP and traffic generating objects?
>

If you generate ftp/telnet traffic as an application running over TCP you
could 
do both of the above. However, in the present ns distribution a API is not yet
built into TCP. But we (out group at baynetworks) have our own version of
tcp-full which
enables you do it. WE generate web traffic in similar lines. You could take
a look at the
code available at ftp://ftp.ee.lbl.gov/IW.tar
I think with the present distribution of ns you cannot do what you want
(some body could
confirm this) but with simple modifications it should not be difficult to
achieve. so for
your presentation purposes 'is ns capable of generating such a traffic?' 
my answer would be YES.

>3- I will create a background traffic in my simulation. I am planning to
>use Traffic/Pareto object. My question is what does happen to dropped
>packets that belong to traffic objects (dropping may caused by either
>queue length limitations or a link going down). Are those packets sent
>again? And is there any other option to create background traffic other
>than Expoential, Pareto and Trace traffic objects? 

Presently, all the traffic generators are built over UDP. So if you drop a
packet you would
not retransmit it. I do not know the exact purpose of the background
traffic, but why can't
FTP traffic be background traffic?? Isn't all the traffic that is of not
your concern a background
traffic? 
You could use CBR sources too to generate background traffic but even they
are built over UDP.

good luck on your presentation
kedar