Re: [ns] ns scalability

[kunchanl <kunchanl@pollux.usc.edu>]

you might want to look at this page (if you haven't) 
http://www.isi.edu/nsnam/ns/ns-largesim.html
, which lists some tips for large simulations


Kun-chan Lan

On Tue, 21 Aug 2001, Huan Pham wrote:

> 
> Hi NS users,
> 
> I have searched through NS mailing-list archieve and have
> found a similar question posted a year ago, but I failed to
> find an answer for that question. So I re-post this question
> again, hopefully someone can give me a hint.
> 
> http://www.isi.edu/nsnam/archive/ns-users/webarch/2000/msg03604.html
> 
> http://www.isi.edu/nsnam/archive/ns-users/webarch/2000/msg03609.html
> 
> As I understand, because NS implements a packet-level
> simulation, the time it takes to run the simulation, and the
> computer power required is proportional to the number of
> packets generated. If I want to simulate a big network (many
> links with large capacity), does it pose a scalability
> problem for NS ?
> 
> Let consider the actual example:
> 
> I have just implemented a small simulation to simulate WEB,
> Audio, and FTP traffic going between Workstation and Node
> n0, The topology is as following:
> 
> 
> # a Lan consists of 20 workstations
> # a 10Mbits Switch
> # a 10Mbits link to outside
> #
> #
> #           n2
> #         \  |
> #          \ |
> #     ... -- n1(Switch) --------- n0
> #          / |
> #         /  |
> #            n21
> #
> 
> If the link utilisation for n1-n0 is 50%, i.e. throughput =
> 5Mbits equivalent to 500 packets /second  (each packet of
> about 1Kbytes ~ 10 Kbits). If I run the simulation for 100
> seconds, since each packet travel through 2 links, NS has to
> handle a total of 2 * 500 * 100 = 10^5 packets .
> 
> The actual time it takes to run on my machine (Pentium III,
> 700MHz, 256M RAM), is 2 minutes
> 
> Now if I want to have a network of 50 routers fully meshed,
> with links of 10Mbits , and link utilisation = 50% , and run
> it for 4000 seconds.
> 
> Total number of links ~ 50 ^ 2 = 2500
> Total number of packets generated = 500 * 2500 * 4000 = 5 *
> 10^9 (packets).
> Expected time to run the simulations = 2(min.)  * 5 * 10^9
> / (10^5) = 10^5 minutes = 600 (days)
> 
> In other words, it is just imposible to run a simulations
> that generate many traffic. Does anyone have any idea about
> this.  Pls reply to my address, (and cc NS mailing list if
> you want to do so). Thank you very much.
> 
>