SPID = Service Profile ID. Originally ISDN was intended to allow multiple devices to share the same ISDN line by connecting together on the user side of the NT1 (S interface). Once the NT1 is built in (U interface, for direct connection to the line)this is generally not possible.
Anyway, since there are so many potential features it was thought that not all devices would support all features. So the system was designed that multiple service profiles could exist on a line, with each service profile having only a specific group of features. Each device would get only the correct features by giving the service profile ID that was appropriate for it.
All of this is ancient history. From a practical matter most lines have 2 SPIDs both of which access the same features (e.g the same service profile) . It is important to understand the fact that the SPID is not a phone number and could in fact be a random number assigned by the Telco. You would still need to enter that(these) number(s) to get the terminal device to work.
*Usually* there are two SPIDs each associated with a separate phone number (e.g. 2 SPIDs and 2 Phone numbers [also called directory numbers].
There are other possibilities such as one SPID and 2 telephone numbers. Or one SPID and one Telephone number. In this last case the line will (usually) respond to 2 calls to that number, like a hunt group between the two channels of the BRI.
When calling a line only the phone number is used. I didn't understand what you meant about getting dial tone the first time, nor in your latest post, so I can't really answer that question. When calling from a telephone into a data device such as a codec I would expect you to get busy or fast busy. Or *Maybe* ring back tone. I certainly would not expect dial tone.
I hope this helps versus confusing you more
If you ask a better question you will get a better reply. Be specific so we can help!
