Almost all providers/ carriers now offer a direct, IP-based network interface, on which Session Initiation Protocol (SIP) is used between the IP-PBX and SIP provider. This IP-based network interface can be used instead of or in addition to the existing ISDN system connections.

The following figure shows an example of this type of network interface:

Native SIP enables IP-based, direct connection between a OpenScape 4000 system and a SIP provider. In an OpenScape 4000 system, the SIP provider connection can, of course, be configured in addition to the traditional ISDN connections.