[ns] ns scalability

[Huan Pham <huan@cs.jcu.edu.au>]

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.