This module has 4 ISDN interfaces which can be connected to standard ISDN2e (BRI) lines providing up to 8 voice channels per module. This allows full integration of your existing ISDN lines into the IPPBX deployment. Incoming calls on ISDN or Vo IP can be distributed to extensions exactly as you wish, & outgoing calls made over ISDN or your Vo IP trunk according to your own preferences.