Possibly the most important single piece of information for a BRI subscriber in the United States is the SPID. SPIDs identify the BRI circuit on the switch along with the circuit ID, and the services that the circuit has assigned to it. For each B channel assigned to the circuit, there is a SPID associated with it, and for each SPID there is an associated telephone number. When you look at the format of a SPID, it looks a lot like a regular telephone number with an added extension. The most common format is 14 digits:
• SPID Format: 91955512120101
• Telephone Number: 9195551212
The last four numbers of the SPID (0101) indicate the sharing terminal ID and the terminal identifier as per the National ISDN Council. When you place a call to another ISDN device, you are placing the call to the telephone number assigned to the circuit rather than directly to the SPID. The SPIDs have local switch significance only.
Depending on how long you have had BRI service, you might not even know that you have SPIDs. By the time the United States reaches a full deployment of NI-3, SPIDs should be automatically downloaded and configured by your device. A lot of equipment already has this function built in, and it depends on the functionality of the switch you are communicating with as to whether or not it will currently work.
With the proper ISDN switch type and the correct SPIDs, your ISDN TA should enter a state that people call synching to the switch. When your ISDN device is synched to the switch, you can place and receive ISDN calls.
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