Re: qos routing

[Kannan Varadhan <kannan@ISI.EDU>]

> From: Luis Henrique Maciel Kosmalski Costa <luish@gta.ufrj.br>
> Date: Tue, 07 Apr 1998 14:10:02 -0300

> 	My problem is as follows. I modified the DV dynamic routing 
> scheme in ns, which is implemented in otcl. My intention was to mesure 
> the efficiency of the new possibles routing schemes indirectly, by 
> means of the quantity of packets lost when a link goes down and the 
> routing algorithm has to recalculate the routes. Best algorithms would
> adapt faster, and the packet loss would be smaller.

Currently, there is no mechanism to dynamically assign costs to the links.
When a node initialises its routing, it uses the cost of the link
as the metric.  If you want to change that to use observed
loss as the metric, you need additional mechanisms to feed that metric 
to the routing protocol instances at each node.

Each route agent on a node has an array of rtPeer objects, one
per peer agent that it distributes routing to.  That peer object
stores the metric to reach that peer.  
Check the ns documentation
(http://www-mash.cs.berkeley.edu/ns/ns-documentation.html)
for the rtPeer objects.
It also has some notes on how that could be changed as well.

> 	But what I observed is that the processing put into the 
> procedure compute-routes in DV has no influence in the packet loss. I
> couldn't explain why. Fact: the routine $ns now returns the same 
> time in the begining and at the end of DV compute-routes.

Since there is no notion of node compute time currently in ns, 
there is no model for packet loss due to lack of routes while
routes are being computed.  You need to add the routines
to appropriately model the problem you wish to address.

> 	Can anyine give me any tips of what is happening? Your help is
> very appreciated.

Hope this helps,


Kannan

--
kannan@isi.edu
http://www.isi.edu/~kannan