# Initialization tasks

An NMS ISDN application performs the following initialization tasks:

- Task 1: Route channel data to on-board resources

- Task 2: Create contexts for channels

- Task 3: Call isdnStartProtocol

- Task 4: Starting NOCC TCPs on B channel contexts

## Task 1: Route channel data to on-board resources

If necessary, the application makes switch connections to route D channel data to the HDLC controller, and to route B channel information to DSP resources. Certain default connections are made automatically if H.100, H.110, or MVIP switching is not enabled. The following illustration shows routing channel data to on-board resources:

For more information, see Making switch connections for NMS ISDN.

## Task 2: Create contexts for channels

The application initializes Natural Access and creates a separate context for each B channel and D channel with which it will interact. The following illustration shows creating contexts for channels:

For more information, see Initializing Natural Access.

## Task 3: Call isdnStartProtocol

The application uses isdnStartProtocol to initialize ISDN protocol stack instances on each D channel context. This function starts up an ISDN protocol stack instance on the D channel context in ACU or LAPD stack mode. In the function call, the trunk is specified using its network access identifier (NAI) and, if duplicate NAI values are defined, the NFAS group number to which this NAI belongs. The following illustration shows calling isdnStartProtocol:

For more information, see Accessing D channels.

## Task 4: Start NOCC TCPs on B channel contexts

The application starts a special no call control trunk control program (nocc TCP) on each B channel context. This program puts the context in a state where voice or media functions can be used without call control. The following illustration shows starting NOCC TCPs on B channel contexts:

For more information, see Starting the NOCC TCP.