The layer 3 user-network signaling procedures for basic call control and for the control and invocation of supplementary services.
 

The term basic call control means that the call will simply be established, maintained, and disconnected. The term implies that a transmission path is created across the network from one user to another. In basic call control, the path is set up immediately. Also, it is set up directly from the calling party to the intended called party. The ITU-T protocols for basic call control are contained in recommendation Q.931.
 
SPIDs

    Service Profile IDs (SPIDs) are used to identify what services and features the telco switch provides to the attached ISDN device. SPIDs are optional; when they are used, they are only accessed at call setup time. The format of the SPID is usually the 10-digit phone number of the ISDN line, plus a prefix and a suffix that are sometimes used to identify features on the line. If an ISDN line requires a SPID, but it is not correctly supplied, then Layer 2 initialization will take place, but Layer 3 will not, and the device will not be able to place or accept calls.