Network sniffing and accounting program

[Arne Goetje <20020531antispam@gmx.net>]

Hi list,

I'm looking for a network sniffing and accounting program.
I am on a shared T1 link and like to have a diagram which shows like MRTG 
the network usage according to the time of the day.
Because I don't have administration rights on the router the program has to 
sniff the traffic and guess the usage out of that data.
I don't care of the protocol distribution or who is connecting to whom. I 
just want to know how much bandwith is consumed during which time of the 
day.
I know there are several sniffing programs, even in debian, but I didn't 
find any yet which displays graphs for the whole backbone usage, only for 
the local host (like 'darkstar').

Does anyone know  a program which might fit my needs?
Any suggestion appreciated.

Cheers
Arne