# ISDN Software product configurations

Using ISDN Software, you can access ISDN services in three ways:

Configuration type | Description
Channelized | Configure ISDN Software so an application can perform call control and other operations using the NCC API. This is the interface described in this manual.
ACU | Access ISDN APIs at the ACU SAPI. Using the ISDN Messaging API, an application can perform a wide range of Q.931 ISDN D channel functions. For more information about this configuration, see the Dialogic® NaturalAccess™ ISDN Messaging API Developer's Manual.
LAPD | Access ISDN APis at the data link layer (Layer 2). Using the ISDN Messaging API, an application can send and receive I-frame data in LAPD messages. This data typically consists of Q.931 messages. For more information about this configuration, see the Dialogic® NaturalAccess™ ISDN Messaging API Developer's Manual.

Specify the configuration to use when initializing the ISDN protocol stack, as described in Initializing the application.