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Caller ID (Caller Identification or CID) is a telephony intelligent network service that transmits the caller's telephone number, and in some places the caller' s name, to the called party's telephone equipment during the ringing signal or when the call is being set up but before the call is answered. Typically, CID is transmitted digitally using Bell 202 modulation between the first and second rings. The term Caller ID was coined by the BellSouth Product team headed by Ellis D. Hill that conducted the first market trial of this service and other "TouchStar" services in Orlando, FL beginning July 7, 1984. This market trial lasted 7 months, after which the results were analyzed and shared with the developer/vendor, Bell Labs/AT&T Network Systems (later renamed Lucent Technologies subsequently purchased in 2006 by Alcatel). Another market trial was conducted in Hudson County, NJ in 1987 by Bell Atlantic (later to become Verizon) followed by limited deployment. BellSouth began the first commercial application of Caller ID in December 1988 in Memphis, TN and was the first RBOC to have it fully deployed. The device is usually helpful for tracing down prank calls, and telemarketers.

Caller ID is also known as Calling Line Identification (CLI) when provided via an ISDN connection to a PABX, while in some countries, the terms Caller Display, Calling Line Identification Presentation (CLIP), Call capture, or just Calling Line Identity (CLID) are used; Call Display is the predominant name used in Canada. CID originated with automatic number identification (ANI) in the U.S. This is not to say that CID and ANI are the same thing. Caller ID is made up of two separate entities: the calling number and the billing (or subscriber) name. When a phone switch sends out a number, the remote telephone company is responsible for looking up the name of the subscriber in a common database. Additionally, nothing ensures that the number sent by a switch is the actual number where the call originated. It is very easy for a telephone switch to send any digit string it requests to the system. For example, if the originating PBX (say, from an office with an ISDN PRI line) sends out 2024561414 as the ANI, then the remote caller ID box will display the White House on the terminal device.

Subscribers can prevent their numbers from being displayed, or "blocked", by dialing a special code before making a call. In North America and some other regions, the code is *67, while the United Kingdom and Ireland use 141. This special code does not block the information from companies using Call capture technology. This means that equipment with Caller ID will simply display the word 'PRIVATE' or 'WITHHELD'. Alternatively, Caller ID can be blocked permanently, and can only be released on a call-by-call basis by dialing a special code (*82 in the U.S.). This is the case in some countries with people who choose not to be listed in the local telephone directory. Similarly, some countries have a service known as anonymous caller rejection, meaning that calls made from a line in which the subscriber's number is blocked, will not be accepted. Blocking of anonymous callers is also becoming a popular feature for caller ID subscribers on a case by case basis as well. Some telephone companies also route anonymous calls to a service which requires the caller to announce him or her self, and then requires the called party to accept or reject the call. Blocking the number is referred to as Calling Line Identification Restriction (CLIR). Emergency services will most likely be able to show the restricted number using a service called Calling Line Identification Restriction Override (CLIRO), or by using general ANI services.

Caller ID between different countries is often not transmitted, meaning that the equipment with Caller ID will simply display either 'UNAVAILABLE' or 'INTERNATIONAL'. However, Caller ID between countries is becoming more widely available, meaning that a telephone number in another country will be displayed, complete with the country calling code. This is usually the case with mobile phones, particularly when a subscriber is roaming overseas. However, the overseas number may be compressed into a 'domestic' format, meaning that the number may not be recognisable to the called party. For example, a US number 1 646 555 1212 may be displayed in the UK as 0646 555 1212, instead of 001 646 555 1212.

Telemarketing organisations often block the display of their calling numbers. Some states and countries require telemarketers to display a contact number that can accept complaints, as the individual caller numbers may not be able to be called.

Many Internet service providers (ISPs) providing dial-up access require the customer to use CLI to prevent abuse of the account by unauthorised callers.

Problems with Caller ID

Some callers have situations in which revealing the number being called from would invade their privacy or cause other severe problems. Caller ID can report falsely when the caller is using a discount or travel calling program or an internet phone (such as Vonage), because those systems use intermediate telephone numbers in the country being called. This can create problems with automated systems (sometimes involving security). For example, a caller calling the Poison Control Center in the USA using a calling card (such as MCI Worldphone) or internet phone (such as Vonage) from another country, will be routed to the poison control center in the state of the number through which the number is being routed. The agent asks questions such as "What is your address?" and then says, "You have reached the wrong poison control center; you will have to re-dial", and cannot by policy help the caller, resulting in an endless loop (July 2003). When Banco do Brasil is called through Vonage from the USA, the call is routed to the São Paulo banking service center, who says the same thing, and will not help the caller who has a bank in Rio de Janeiro, and then finds it impossible to get through (July 2005). Cox Cable in Arizona, USA, upon receiving a call through Vonage said, "We cannot help you because you are not calling from the phone at the address of service." (Jan 2001), and MCI Worldphone said, "We have a security issue with your account being used from two different countries in the same hour." Callers calling friends often get, "Where are you calling from? Are you sure, because the caller ID shows you are calling from another state in my country." Because there are a myriad of automated systems for dealing with caller ID, and no standard, issues like these--and much more complex ones when it comes to large systems interacting--occur frequently.

Hacking Caller ID

Caller ID is actually a very simple string of code and can be read and generated very simply by small computer programs and even some inexpensive devices. Although the caller ID information is transmited in between the second and third rings, before the phone call is connected, it is possible to mislead the phone company as to the origin of the call, thus defeating caller ID. Misleading the phone company by generating ANI code or by other electronic means is very complex, simpler means do exist. Using a services like Vonage or Skype, calling from a payphone, or using a calling card are easy means to fool caller ID.

Disabling Caller ID

In North America, there is one code to disable Caller ID. The code is *67. In the United Kingdom and Ireland, 141 is the equivalent code. Other countries and networks may vary. On GSM mobile networks you dial #31# before the number you wish to call to disable it.

Type II Caller ID

In 1995, Bellcore released another type of modulation similar to Bell 202 in which it became possible to transmit Caller ID information and even provide call-disposition options while the user was already on the telephone. This service became known in some markets as Call Waiting ID or when it was combined with call-disposition options; Call Waiting Deluxe.

Values in design

See also

  • Calling ID is the identification of who you are calling, or connecting to, as opposed to caller ID identifying who calls you.
    • Examples: 1) When you call someone using Skype you can see the other party's details, and even an image such as a photograph that they have chosen to represent their identity. 2) When you connect to a web site the identification of the site you are visiting can be displayed on your browser telling you who owns the site you are visiting.
  • The inverse feature, giving the number originally dialed, is known as Direct Inward Dialing (DID), Direct Dialing Inward (DDI), or Dialed Number Identification System (DNIS). This tells the PBX where to route an incoming call, when there are more internal lines with external phone numbers than there are actual incoming lines in a large company or other organisation.
  • List of telephony terminology
  • As a sidenote: Not all types of caller identification use 202-type modulation, nor do all systems send the information between the first and second ring, e.g., British Telecom sends the signal before the first ring, after a polarity reversal in the line. As a result, not all "CallerID" devices are compatible from country to country or in the same country, even though the basic phone system is the same. Some providers use FSK, others use the DTMF protocol.
  • This is not to be confused with Microsoft Caller-ID, a patent encumbered E-mail authentication technology. For the history of this now dead proposal see MARID.
  • Caller ID spoofing

Telephony | Authentication methods | Telephone service enhanced features

Caller ID

 

This article is licensed under the GNU Free Documentation License. It uses material from the "Caller ID".

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