6.2. Call Detail Transmission 
It is strongly recommended the connectivity is made via the Customer
Lan (CLAN) and not the OpenScape 4000 Atlantic Lan (ATLAN).
Through using the CLAN, the Linux firewall only allows communication
to the outside world through specific ports, thus protecting the internal
ATLAN communication from external issues that can affect telephony stability.
The flexibility of using CLAN also allows any CDR collection devices
to be in an independent LAN segment. It is understood, legacy installations
that previously used the ATLAN will continue to do so.