delay and collisions in LANs?
13 Oct 1998 11:54:41 -0700
Verena Rose <email@example.com> writes:
> could anybody help me with the definition of the delay in LANs in ns.
> With make-lan there comes among others a parameter for the delay. How is
> this one
> I'm not sure about it because there is another parameter in the Channel,
> the propagation delay. Is this the time a bit needs to go from one
> station to another on the cable?
Let me first say that I'm talking about LANs as they are implemented
in the current ns/nam snapshot.
If there is no contention, the total time should be:
Channel::delay_ + // both Channel and Mac delays reflect the
Mac::delay_ + // medium access characteristics (order of
LL::delay_ + // this is delay from make-lan
txtime(packetsize + Mac::hlen_) // transmission time
> Another problem I have is with collisions. I have a LAN with four nodes,
> and two FTP and one CBR application running there. There seem to be some
> collisions when I look at nam, but there are no collisions and therefore
> no retransmissions in the tracefile.
> Is this because collisions cannot be drawn exactly by nam or do I have
> to modify something in the MAC or LL?
Both. Nam cannot show collisions yet, and they are not traced. It
depends on how you look at it: current tracing is done at the IP level,
so drops and re-transmissions done by MAC are not traced, and you'll
need to add them yourself.