RE: [ns] TTL and ns

[Michael Welzl <michael@tk.uni-linz.ac.at>]

> I have a problem regarding the way ns-2 handles the TTL field:
> 
> Please consider the following topology (TCP/Reno):
> 
>    Sender-----Node 1------Node 2------Sink.
> 
> Intuitively, an initial TTL of 3 should be sufficient. However, ns
> requires TTL set to 4, otherwise the packet will be dropped 
> at the Sink.
> 
> In real world - I assume - a TTL=3 should work.
> 
> Is this an inconsistency betweek ns/realworld, or am I wrong about my
> "real world" assumption?

I believe it is an inconsistency because in ns, TTL is handled in a link,
not a router. In your example, there would only be two real-world routers
handling the packet, while there are three ns-links.

Kind regards,
Michael Welzl