Assumption about the underlying network?

["Huiwen Li" <huiwenli@nortelnetworks.com>]

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?

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? 

Please give me an idea. Thank you very much.

Huiwen