I'm at work and imageshack is blocked

happy but based on what you say.
The issue is with replication, not updating. My bad.
When replication occurs from A > B then the line is flooded....
Have you checked that replication is setup as incremental?
If using ePO4, select Automation, then your replication task. under Actions, you can choose incremental to all or some distributed repositories.
I've got mine set to incremental (and has been for years). The only thing that causes it any stress is when I install a new piece of major software - otherwise it tends to be just the DATS replicating....
If you have full replication every time that thats a lot of data to copy every time...
The only other thing I think it might be if you are going to all repositories and you had lots of them - then the line out from your ePO Server could get congested.