Question : Reducing bandwidth consumption between domain controllors at multiple sites

We have an 2003 SBS server running at a client's primary site, with 8 other satellite offices (each several miles apart).

Each office including the primary is running ADSL.

We have recently installed Windows 2003 Server R2 Std domain controllers, one for each office - local computers are logging into the local domain controller.

Everything is working perfectly, except the amount of bandwidth used between offices has rocketed by 2gb/day.

I've added each server to it's own site, subnet and associated a cost and replication period (3 hours).

Can anyone recommend:

a) Software to breakdown the content of the traffic (we use Draytek 2820 routers which only give an overall usage).

b) Tips to reduce unnecessary chatter between the servers.

The servers are all configured as DNS servers with zone transfer enabled. All offices are VPN'd back to the primary. One office has a VPN link to every other office. This uses no more or less bandwidth. Should we consider replicating this setup to all offices?

Thanks

Answer : Reducing bandwidth consumption between domain controllors at multiple sites

thanks for the update, feel free to close the question down and award yourself the points OR you can give me some ;-)