Re: [ns] send /recv

[Haobo Yu <haoboy@isi.edu>]

> >From a lot of source code, I find if you want to send data, you just call
> target_->recv(p). Does this mean after we finish generating topology, the
> target_ value in every NSobject(Connector) is already evaulated by NS,the
> user does not need to know its value. Sorry for asking this question
> again, since I could not find where to tell the detail.

Routing may not necessarily be setup after topology is created. It'll be
safe to access routing tables after simulation started (i.e. $ns run)

> the second question is basically how to decide what should be simulated in
> an application. since in NS , it is only delay and size, while  usually in
> an real application we need very complicate algorithm to implement it. of
> course , if we can evaluate the delay for some operation ,like
> encryption,then we do not need to implement the encryption algorithm.
>
> Actually what I want is to do multicast group key management.There is a
> centralised key manager to update group key corresponding  to every
> joining/leaving in a very dynamic group. The manager needs a very big
> key tree, hash table and other data structures in the real model, 
> also needs a lot of work in traversing the tree and other stuffs. So I
> wonder if I need to do the real thing or how can I simulate it?

Well, it depends on what you want to evaluate. Simulations are always
abstractions of the real world so you have to leave out something. In what
you just said the only thing I can say is if you have a computation time
model for your encryption algorithm, then of course you don't need the
real thing, otherwise you probably have to implement that if that time is
very important to you.

However, this may mean your simulation won't scale. So if evaluation of
scalability is one of your major concerns, you probably want to use a
simple model for computation time and focus on what you are interested.
It's always possible to adjust that computation time model and evaluate
its impact on your results. 

Hope this helps.