Re: [ns] TTL question

[Haobo Yu <haoboy@packetdesign.com>]

I think it's a simulator artifact. TTL is checked in ns in this way:

  ---->
n1      n2
  <----

each simplex link is basically:

queue -> link delay -> ttl

When the ttl object gets a packet, it first decreases the packet ttl
count, then if the count drops to 0 it drops the packet. 

From (2) to (3) there are 3 links, thus a ttl=3 packet will be dropped at
the 3rd link.

Unfortunately I don't know why it's like this, and I don't know if anyone
knows... :(

- Haobo

On Tue, 24 Oct 2000, Scott Michel wrote:

> Here's a "feature" that confuses me a little, and perhaps I'm misunderstanding
> the simulator's operation. Here's my topo (again):
> 
> 
> (2)              (3)              (6)
>   \               |               /
>    ---- (0) ---- (4) ---- (5) ----
>   /                               \
> (1)                              (7)
> 
> At each of these nodes, there are agents sending packets with small numbered
> TTLs. When (2) sends a multicast packet with TTL 3, node (3) never sees it,
> although from what I understand of things, it should. If node (2) sends with
> a multicast packet with TTL 4, node (3) does receive it.
> 
> Is this a misunderstanding on my part of how TTL is supposed to work or just
> a simulator artifact?
> 
> 
> -scooter
> -- 
> Scott Michel                          |   No research ideal ever survives 
> UCLA Computer Science                 |   contact with implementation.
> PhD Graduate Student                  | !!  Futuaris nisi irrisus ridebis  !!
> 
>