# Starting a management session

Call imgtStart to start an IMGT session. The function takes as arguments the network access identifier (NAI) and the pointer to a configuration structure (IMGT_CONFIG structure). The configuration structure enables applications to filter any IMGT events that the application receives. After invoking imgtStart, the application can use imgtSendMessage to send messages to the IMGT service.

## Network access identifiers (NAIs)

A trunk is referred to by its NAI. To initialize an ISDN protocol stack instance for a context (using isdnStartProtocol), specify the NAI of the trunk to associate with the context. From then on, the application can communicate with the D channel on that trunk by specifying the associated context handle. For example, when an event is received, the context handle indicates the trunk on which the event occurred. For more information about using isdnStartProtocol, see the NMS ISDN Messaging API Developer's Reference Manual.

Different board types support different numbers of D channels with different corresponding NAI numbers. The following table shows what each board type supports:

Digital trunk interface board type | Number of D channels | Default NAI values | Number of NFAS groups
--- | --- | --- | ---
Four-trunk boards | 1 to 4 | 0 to 3 | 1 to 4
Two-trunk boards | 1 or 2 | 0 or 1 | 1 or 2

If your configuration involves NFAS groups, the NAI for each group is specified in the system configuration file. For more information, see the NMS ISDN Installation Manual.