Caller ID services or (CID), also known as Calling Line Identification services (CLID), are services provided by the telephone companies that enable the recipient of a telephone call to identify the party calling them, either by name or by telephone number. The different types of caller ID services available are analog, digital, Voice Over Internet Protocol (VOIP) caller ID, Automatic Number Identification (ANI), and call waiting ID. Each type has different benefits and disadvantages.
Basic types of caller ID services such as Calling Number Identification (CNID)identify the party who is calling by looking up the billing information associated with the telephone number. Available for both analog and digital telephone, if the call comes from a standard loop telephone line, called a POTS exchange, the local switch of the service provider provides the identification details. The actual connection is made only when the recipient answers the phone, so the caller cannot alter this type of caller identification, although it is possible to block it.
ANI is the identification of callers based on their phone numbers. This type of telephone service is a very basic form of caller number identification, which was first created for internal testing purposes by telephone maintenance workers and later used by AT&T for long distance billing. The calling phone numbers are captured by the destination telephone company and can be accessed by the recipient of the call even if regular caller ID services are blocked.
The use of caller ID services in the VOIP environment is unregulated and easy to fake, such as configuring false phone numbers in order to avoid long distance charges. VOIP is the delivery of phone services across the Internet. This means callers and recipients can use devices other than telephones to chat, and programs available for VOIP telephone calls include Skype and MSN. For this reason, caller identification of VOIP calls may be fake and is not reliable.
Call waiting ID services, otherwise known as Type II caller ID services, date back to 1995 when it became possible for the telephone service provider to transmit the identification details of the caller after the user was already on the telephone. This works by combining call waiting services with caller ID services, and usually has an option for the recipient to select whether or not to answer the call, toggle between the current call and the waiting call, forward the new call to voice mail, or disconnect it entirely.