Samba over leased line

[Andreas Vierengel]

We have two Class C nets (192.168.1.0/24) and 192.168.2.0/24). These nets
are connected through a pair of router (BinTec) via ISDN.
The router have a short hold mode, i.e. cancels the line if no packets are
to be received or transmitted.
Recently we installed one Samba Server in a subnet. In the other subnet are
several clients, which print to the samba-server (via the ISDN link).
We have not much traffic during the day, but our server seems to open the
ISDN line at least every 3 minute.

our smb.conf:
[global]
   debuglevel = 1
   workgroup = edv
   security = user
   username map = /usr/local/samba/lib/user.map
   allow hosts = 192.
   guest account = sambapc
   os level = 38
   null passwords = yes
   preferred master = yes
   remote announce = 192.168.255.255  <= if I cancel this line i cannot
reach the samba server from my clients

; Printing
   printing = bsd
   printcap name = /etc/printcap
   load printers = yes
   log file = /usr/local/samba/var/log.%m
   locking = yes
   lock directory = /usr/local/samba/var/locks
   share modes = yes
   protocol = NT1

the rest are some shares.

it appears that every 3 minutes the samba server spokes from port 139 to
192.168.255.255 for remote announce.

How can I setup samba, that I can see the samba server from my remote
clients AND prevent it to produce traffic over my leased lines (our
telephone bill is very high at the moment due to German Telecom :-(

Thanks in advance

--Andy