hi...
The Service Profile IDentifier (SPID) is a number assigned to a fully initializing ISDN terminal that enables the Stored Program Control Switching System (SPCS) to uniquely identify the ISDN terminal at layer 3 of the D-channel signaling protocol.
Each fully initializing terminal needs to be uniquely identified at layer 3 in order for the SPCS to provide terminal-dependent features. When the terminal sends its SPID during layer 3 initialization, the SPCS uses the SPID to associate the terminal with a specific set of terminal services (that have been previously provisioned in the SPCS for that terminal). The directory number of the terminal is not sufficient for this purpose because directory numbers may not uniquely identify a terminal on an interface; that is, a directory number can appear on multiple terminals on a single BRI.
SPIDs also simplify switch-based troubleshooting when multiple terminals are assigned to a BRI. Abnormality logs in the SPCS indicate the SPID of a terminal experiencing a problem. This information helps maintenance personnel isolate and resolve ISDN troubles.
One example of a configuration where different terminal-dependent features need to be assigned follows: Two voice terminals are served by a single BRI. The terminals share the same directory number, but only one terminal is provided with access to call hold and flexible calling (conference calling) features. A separate set of characteristics--or profile--is provisioned in the SPCS for each terminal. One profile includes call hold and conference calling; the other profile does not. When each terminal initializes, the SPCS uses the terminal's SPID to provide the correct features and button assignment to the terminal. There are many other examples of features that are assigned in a similar manner.
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Devang
