Caller ID allows the person being called to see the number (and sometimes the name) of the person calling them, when they have the correct equipment to receive the callerid information. Caller id is often an added value (i.e extra cost) service from your telco. You can usually withhold sending of the caller id on outgoing calls by dialling a special code before the number.

There are many different callerid systems in use around the world. The callerid FAQ gives a lot of useful information.

• Note that on the PSTN, CNAM (Caller NAMe) data is looked up via caller ID digit information out of a database by the serving CO. It cannot be set by the user.

On ISDN PRI lines (US NI-2 type) Callerid name information CNAM is transmitted in a separate FACILITY IE. some time AFTER the initial SETUP message. If you are using CNAM in your dialplan make sure to insert a wait statement before using the calleridname variable. Otherwise CALLERIDNAME will not be populated initially.

i.e.:
exten => _X.,1,NoOp,${CALLERIDNAME} ; will be empty. - FACILITY IE has not been received yet.
exten => _X.,2,Wait(1) ; wait for the CO to find the name in the database
exten => _X.,3,NoOp,${CALLERIDNAME} ; now it shows the name

If you are using a VOIP provider, the CID information is sent with the call setup. Note however that most VOIP providers will not send a caller ID name, only the number. This is because they do not have name exchange agreements in place. If you want to get caller ID information in this case, use a reverse number lookup tool. Take a look at smartCID from www.generationd.com as an example.

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See also:

• CNAM - Caller ID Name
• CNAM Lookup - CNAM Lookup script
• ANI - automatic number identification
• Asterisk hardware - for hardware that supports caller id
• Asterisk and UK Caller ID
• Asterisk and Australian Caller ID
• Caller Name DIP API (Fast AGI/ AJAX)
• Caller ID lookup script (reverse phone number lookup) and local database
• Free CNAM Project Free private-database CNAM dips for non-commercial uses.
• US Reverse Lookup AGI - 411.com, google.com, and anywho.com with caching and NANPA lookups
• US Reverse Lookup AGI + MySQL - Revision of the above script to include MySQL caching as well
• US and Canada Reverse Lookup with Spam Estimate - Revised Ultimate CNAM Consults multiple local and external sources
• Asterisk bounty non-Bellcore-CLID
• Swedish CLID spec
• The Caller ID FAQ
• CID Issues with some Siemens DECT phones in France