[ns] Re: Multiple Multicast sessions

[Haobo Yu <haoboy@isi.edu>]

> what i find is that sessions with "smaller" id (i.e., those which were
> started first by the simulator based on the for-loop variable) have lower
> losses.

I guess you must be using CBR sources right? In such cases because you do
not insert any randomness into packet generation the ordering of packets
on the aggregate link from all flows are deterministic and you should
expect to see the same drop pattern throughout your simulation. This would
result in what you've seen.

Now you are in charge of your simulation and you can change your cbr
traffic source to add in randomness, say, packet intervals, while maintain
the same average rate. Is that one of the reasons you saw randomness in
real-life traffic?

Please let me know if I missed anything.

- Haobo

> The obvious conclusion is that the packet events for the sessions which
> were started earlier are scheduled earlier. since I am modelling bursty
> traffic, these packets fillup the queue causing other packet events
> scheduled at the same simulated time, to incur losses.
> 
> In a real-life situation one may expect these losses to be distributed
> "randomly" among all the competing sessions. so how do i make this random,
> instead of this deterministic outcome?
> 
> I tried using a "Heap" scheduler, but the results are the same.
> is there anyway out of this?
> Any help will be appreciated. Thanks in advance.
> 
> -Srinivasan
> 
>