I have few projects ideas that involve plugging a computer or an arduino to my landline phone (or just before it). For example, I would like to grab the caller ID sent when someone calls, do a lookup on the web or in an address book, and display the associated name on a LED screen.
The problem is that I can’t find any resources on the protocols used for transmitting this caller ID, etc. I may have misused my google skills, so could anyone give me some pointers ?
I am particularly interested in all the protocols evolving around landline phones (caller ID forwarding/blocking, sending SMS, starting/ending a call, etc.). It is my understanding that while the long distance part (from central to central) is numeric, the signal reaching the phone on the customer side is still analogic. Is it true ?
The majority of public telephone networks (PSTNs) have a digital core (switch to switch) and an analogue edge (from the edge switch to your phone at home).
Business and large campuses (Hotels, Hospitals, Colleges – any large organization on a single or closely located sites) often will have a local phone system and switch (PABX) which will speak digitally to the edge exchange and which, increasingly, may speak digitally to the desk phones also.
There are actually a number of different standards in use for sending the CLI over the analogue circuit to your home phone depending on where you are and who your operator is – see the following link as a good starting point, although it is old and the links appear broken):
http://www.ainslie.org.uk/callerid/cli_faq.htm#Q_6
This one may also be useful:
http://www.tech-faq.com/fsk.html