Re: Assumption about the underlying network?

[Tarik Alj <aljtarik@ozias.inrs-telecom.uquebec.ca>]

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> To: "Huiwen Li" <huiwenli@nortelnetworks.com>
> Cc: "'ns-users@mash.cs.berkeley.edu'" <ns-users@mash.cs.berkeley.edu>
> Subject: Re: Assumption about the underlying network? 
> Date: Fri, 24 Sep 1999 10:57:42 -0700
> From: John Heidemann <johnh@isi.edu>
> 
> On Tue, 21 Sep 1999 11:35:06 PDT, "Huiwen Li" wrote: 
> >Hello,
> >
> >I am trying to simulate a network from the upper layers, not touching lower
> >2 layers of the network. But my simulation requires the underlying network
> >is Ethernet. I am wondering if I am simulating at the upper layer (IP, TCP),
> >what is the assumed about the underlying network? Can I set packetsize for
> >the underlying network, like for Ethernet, about 1544 bytes?
> 
> Yes, you can set the packet size on a per-agent basis.
> 
> >Another question I have is about the LAN simulation. Is it possible for me
> >the establish a complicated topology from the lower layer using make-lan? It
> >seems to me that LAN simulation is only for a simulation inside a LAN, not
> >able to do routing? Is there any such example?

Lans use a special object called LanRouter to find the "nexthop" inside the LAN,
the thing is that LAN connectivity is represented by virtual links that don't 
appear when populating the address classifier. That way the Classifier in each 
node only knows of the point-to-point links. And inside the LAN, the LanRouter 
object is used. So you can incorporate LANs into more complicated topologies. 
The cost of going thru a LAN is also always of 1. 

Check out vlan.tcl, this will seem less complicated; there is also a few 
postings from Yuri Pryadkin on the subject that can be very helpful.

Use new-lan instead of make-lan, for precision.

good luck
  
> 
> LANs should be able to do routing.  You can find examples by grepping
> for "make-lan" in ~ns-2/tcl/{ex,test}.
> 
>    -John Heidemann

Tarik