Re: Supporting large very large number of nodes

[Polly Huang <huang@catarina.usc.edu>]

> I've run multicast simulations with 1680 nodes under the normal
> simulator with recent snapshots, and _some_ of them have worked,
> albeit inconsistently;  running-out-of-memory problems, I suspect,
> since there are rather a lot of link objects too.
> 
> For large simulations where you're not interested in queuing delay,
> you should apparently use SessionSim, which discards queueing
> information etc to save memory. (Contrary to nsDoc, first part of
> chapter 23, up to and including the latest release of 29 September,
> SessionSim does not discard propagation delay - so I'm looking at it
> with renewed interest.)

Lloyd, thanks for clearing it out.  SessionSim does take into account 
propagation delay and this bug in nsDoc has been fixed and will appear in
the next nsDoc release.

As for the simulation scale, the following table is recently updated and I
thought should be helpful to Arnis and other ns-users.

# Created by Polly Huang, USC/ISI
# http://www-scf.usc.edu/~bhuang
# 7/16/98

ns Scaling - The Story

The bottleneck has been determined to be the routing table, which is
O(n^2) for flat routing. 

In addition, n (number of routing entries) is always 2^k. That is why 
we observe roughly the same routing table size for 513-node and 
1024-node simulations (k=10).

The following table lists _approximately_ the memory consumption of
session sim with various memory conservation solutions.

# nodes in topo		Mem consumption (in MB)
		detailed	session		session+hier	 session+algo
512-1023	 189		   16		   9 (1000 node)	  6 (1000 node)
1024-2047	 656 		   46		  22 (2000 node)	 10 (2000 node)
2048-4095	2432		  180		  77 (4000 node)	 18 (4000 node)
4096-8191			  720		 190 (6000 node)	 33 (8000 node)
8192-16384			 2886		1049 (10075 node)	 82 (20000 node)
									217 (50000 node)
cheers,
-Polly

> 
> You'll need to use one of:
> # traditional, deprecated
> Node expandaddr
> 
> # new fashionable equivalent object syntax
> $ns set-address-format expanded
> 
> # gives 1024 nodes with patch to support one level of hierarchy;
> # (bit reserved for multicast) I haven't played with multiple levels.
> $ns set-address-format hierarchical 1 11
> 
> after initialising the simulator to get a large address space to
> create the nodes in.
> 
> hth,
> 
> L.
> 
> > On Thu, 15 Oct 1998, Arnis Ziedins wrote:
> > 
> > > Does somebody have  experience of running ns script with a very large number
> > > of nodes? 
> > > 
> > > How many nodes running TCP can be simulated with ns?
> > > For my experiment I would like to  have more than 1000 nodes.
> > > Is it feasible with ns?
> 
> <L.Wood@surrey.ac.uk>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>
> 
>