Caller ID (caller identification, CID, or more properly calling number identification) is a telephone service, available on POTS lines, that transmits a caller's number 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. Where available, caller ID can also provide a name associated with the calling telephone number, for a higher fee. The information made available to the called party may be made visible on a telephone's own display or on a separate attached device.
Caller ID may be used to track down or limit the impact of prank calls, telemarketers, and other intrusions. However, it can also impede communication by enabling users to become evasive. The concept behind caller ID is the value of informed consent; however, it also poses problems for personal privacy. Another problem is that the possibility of caller ID spoofing makes it unreliable.
However, CNID and ANI are not the same thing. Caller ID is made up of two separate pieces of information: the calling number and the billing (or subscriber) name where available. When an originating phone switch sends out a phone number as caller ID, the telephone company receiving the call is responsible for looking up the name of the subscriber in a 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 initiating the call to send any digit string desired as caller ID.
What is displayed as caller ID also depends on the equipment originating the call.
If the call originates on a plain old telephone service line (a standard loop start line) caller ID is provided by the service provider's local switch. Since the network does not connect the caller to the callee until the phone is answered generally the caller ID signal cannot be altered by the caller. Most service providers however, allow the caller to block caller ID presentation through the vertical service code *67.
A call placed behind a private branch exchange (PBX) has more options. In the typical telephony environment a PBX connects to the local service provider through PRI trunks. Generally, although not absolutely, the service provider simply passes whatever calling line ID appears on those PRI access trunks transparently across the Public Switched Telephone Network (PSTN). This opens up the opportunity for the PBX administrator to program whatever number they choose in their external phone number fields.
IP phone services like Vonage support PSTN gateway installations throughout the world. These gateways egress calls to the local calling area, thus avoiding long distance toll charges (a key feature of the Vonage service). Vonage also allows a local user to have a number located in a foreign exchange; the New York Caller could have a Los Angeles number. When that user places a call the calling line ID would be that of a Los Angeles number although they are actually located in New York.
With Cell phones the biggest issue appears to be in the passing of calling line ID information through the network. Cell phone companies must support interconnecting trunks to a significant number of Wireline and PSTN access carriers. In order to save money it appears that many cell phone carriers do not purchase the North American feature Group D or PRI trunks required to pass calling line ID information across the network.
In 1968, Theodore George “Ted” Paraskevakos, while working in Athens, Greece as a communications engineer for SITA, began developing a system to automatically identify a telephone caller to a call recipient. After several attempts and experiments, he developed the method in which the caller's number is transmitted to the called receiver's device. This method was the basis for modern-day Caller ID technology.
From 1969 through 1975, Paraskevakos was issued 20 separate patents related to automatic telephone line identification; they are listed below.
|Country||Patent number||Issue date||Description|
|Greece||40176||May 28, 1969||Apparatus for the decoding and display of the identification of calling telephone devices in the receiving device|
|Greece||37541||June 19, 1969||Apparatus for the decoding and display of the identification of calling telephone devices in the receiving device|
|Greece||37733||June 27, 1969||Method of automatically transferring by electrical pulses the identification of a calling device and automatic display in the receiving device in automatic urban and long distance telephony|
|Greece||38280||October 16, 1969||Method of automatically transferring by electrical pulses the identification of a calling device and automatic display in the receiving device in automatic urban and long distance telephony|
|Greece||39092||January 26, 1970||Method of automatically transferring by electrical pulses the identification of a calling device and automatic display in the receiving device in automatic urban and long distance telephony|
|Greece||42452||September 8, 1970||Apparatus for the decoding and display of the identification of calling telephone devices in the receiving device|
|France||2.133.267||April 15, 1971||Procédé et appareil pour enregistrer le numéro du poste téléphonique dont un appel provient|
|Japan||22983/1971||May 17, 1971||Improved apparatus for generating and transmitting digital information|
|France||2.152.356||September 7, 1971||Pulse train generating and selection apparatus|
|Greece||43263||September 10, 1971|
|Greece||43999||February 10, 1972||Apparatus and method for automatically displaying the identification of a calling device in the receiving device|
|South Africa||71/3894||May 3, 1972||Improved apparatus for generating and transmitting digital information|
|Italy||935035||December 1, 1972||Apparatus perfezionato per generare e trasmettere informazioni numerche|
|United States||3,727,003||April 10, 1973||Decoding and display apparatus for Groups of Pulse Trains|
|Canada||938363||December 11, 1973||Decoding and display apparatus|
|France||7132207||January 4, 1974||Appareil perfectionné de production et de transmission ď information numérique|
|United States||3,812,296||May 21, 1974||Apparatus for generating and transmitting digital information|
|Great Britain||1362411||December 4, 1974||Apparatus for decoding and display of digital information|
|Great Britain||1362412||December 4, 1974||Pulse Train generating and selection apparatus|
|Australia||458,841||July 24, 1975||Telephone system|
Since Paraskevakos' patents significantly predated all other similar patents, they appear as prior art in later U.S. Patents issued to Kazuo Hashimoto and Carolyn A. Doughty.
In 1971, Paraskevakos, working with Boeing in Huntsville, Alabama, constructed and reduced to practice a transmitter and receiver, representing the world's first prototypes of caller identification devices. They were installed at Peoples' Telephone Company in Leesburg, Alabama and were demonstrated to several telephone companies with great success. These original and historic working models are still in the possession of Paraskevakos.
In the patents related to these devices, Paraskevakos also proposed to send alphanumeric information to the receiving apparatus, such as the caller's name, and also to make feasible banking by telephone. He also proposed to identify the calling telephone by special code (e.g., "PF" for public phone, "HO" for home phone, "OF" for office phone, "PL" for police).
In May 1976, Kazuo Hashimoto, a prolific Japanese inventor with over 1000 patents worldwide, first built a prototype of a caller ID display device that could receive caller ID information. His work on caller ID devices and early prototypes was received in the Smithsonian Institution, National Museum of American History in 2000. U.S. patent 4,242,539, filed originally on May 81976, and a resulting patent re-examined at the patent office by AT&T, was successfully licensed to most of the major telecommunications and computer companies in the world.
Initially, the operating telephone companies wanted to have the caller ID function performed by the central office as a voice announcement and charged on a per call basis. John Harris, an employee of Northern Telecom's telephone set manufacturing division in London, Ontario promoted the idea of having caller ID as a telephone set display. The telephone was coded ECCS for Enhanced Custom Calling Services. A video of his prototype was used to leverage the feature from the central office to the telephone set.
Early in 1977 Nélio Nicolai, a Brazilian inventor, created a machine capable of identifying and displaying the caller ID, he named it BINA (B identifies number of A). He patented the invention, but lack of support from the Brazilian patent-issuer authority INPI made him pursue the judicial system to effectively collect the royalties from his invention (the lawsuit is still running). He received many proposals to drop his wish for a full patent recognition, but did not accept any. The first commercially available BINAs appeared in 1982 in the Brazilian capital, Brasília. In 1996, Nélio received the WIPO (World Intellectual Property Organization) award for his invention. There is an ongoing debate on how Bell Canada approached Nélio and its former employer (Telebrasília) in the mid-80s asking for technical papers and prototypes (Nélio travelled to Canada). Experimental use of the system happened at the Canadian city of Peterborough, Ontario. Talks ceased and surprisingly, in 1986, Bell Canada announced such tests to the general public, with following commercialization starting in 1988. Nélio says that no royalties were ever collected.
The first market trial for caller ID and other "TouchStar" services was on July 71984 in Orlando, Florida. Ellis D. Hill, the head of the BellSouth Product team, coined the term caller ID. This market trial lasted seven months. It was conducted and analyzed by Bell Labs/AT&T Network Systems. In 1987, Bell Atlantic conducted another market trial in Hudson County, New Jersey, which was followed by limited deployment. BellSouth was the first company to deploy caller ID in December 1988 in Memphis, Tennessee, with a full deployment to its 9-state region over the next four years. Bell Atlantic was the second local telephone company to deploy Caller ID in New Jersey's Hudson County. US West Communications (now Qwest) was the third local telephone company to offer caller ID service in 1989.
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; it is technically referred to as Analog Display Services Interface.
In the United States, caller ID information is sent to the called party by the telephone switch as an analog data stream (similar to data passed between two modems), using Bell 202 modulation between the first and second rings, while the telephone unit is still on hook. If the telephone call is answered before the second ring, caller ID information will not be transmitted to the recipient. There are two types of caller ID, number only and name+number. Number only caller ID is called Single Data Message Format (SDMF), which provides the caller's telephone number, the date and time of the call. Name+number caller ID is called Multiple Data Message Format (MDMF), which in addition to the information provided by SDMF format, can also provide the directory listed name for the particular number. Caller ID readers which are compatible with MDMF can also read the simpler SDMF format, but an SDMF caller ID reader will not recognize an MDMF data stream, and will act as if there is no caller ID information present, e.g. as if the line is not equipped for caller ID.
Instead of sending the caller ID in between the first and second ring, some systems use a "line reversal" to announce the caller ID, or caller ID signals are simply sent without any announcement. Instead of Bell 202, the European alternative V.23 is sometimes used, (without the 75 baud reverse channel) or the data is sent using DTMF signalling.
In general, CID as transmitted from the origin of the call is only the calling party's 10-digit phone number. The calling party name is added by the consumer's terminating central office if the consumer has subscribed to that service. Calling name delivery is not automatic. An SS7 (or Signaling System 7) TCAP query must be launched by the called party's central office to retrieve the information for Calling Name delivery to the caller ID equipment at the consumer's location. Canadian systems automatically send the calling name with the call set up and routing information at the time of the call.
To look up the name associated with a phone number, the carrier in some instances has to access that information from a third party database and some database providers charge a small fee for each access to such databases. To avoid such charges, some carriers will report the name as unavailable, or will report the name as "(city), (state)" based on the phone number. For 800 numbers, they may report a string such as "TOLLFREE NUMBER" if the name is not available in a database.
Some telemarketers have used caller ID itself for marketing, such as by using an 800 number and the text string "FREE MONEY" or "FREE PLANE TICKETS" as the name to be displayed on the 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 falsely report when the caller is using a discount or travel calling program or a voice over IP phone, because those systems use intermediate telephone numbers in the country being called.
Blocking is the common term for preventing the display of a calling number.
Telecommunications regulators vary in their requirements for the use and effectiveness of assorted technologies to prevent numbers from being displayed. There is also varying treatment for equation of call display blocking with non-published numbers; in some areas, having a non-published number does not mean call display blocking will be automatic, so customers should inquire carefully to make sure their non-published number is not being displayed and if it is, what steps to take to block the number.
In Canada, the Canadian Radio-television and Telecommunications Commission requires blocking to be customer-activated for each call, although there is an exception for telephone lines at shelters for victims of domestic violence. Such lines can be programmed to always block, without the use of an activation code at the time a call is placed.
In some locations in the United States, regulators allow (or require) blocking to be automatic, transparent to the caller.
Where blocking is applied on a call-by-call basis (at the time a call is made), subscribers can block – prevent their numbers from being displayed – 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". When CNID is blocked at the caller's request, the number is actually transmitted through the entire telephone network, with the "presentation withheld" flag set; the destination CO is expected to honor this flag, but sometimes does not – especially when the destination phone number is served by an ISDN primary rate interface.
Alternatively, in cases where caller ID is being blocked automatically, it can only be released on a call-by-call basis by dialing a special code (*82 in the U.S.; 1471 (1571 is an optional answer phone service) in the UK). See Disabling, below.
Similarly, some countries offer anonymous caller rejection, which rejects all calls when the subscriber's number is blocked. Some telephone companies protect their clients from receiving blocked information by routing anonymous calls to a service, where the caller is required to announce him or herself. The service then asks the called party if they want to accept or reject the call. Blocking the number is referred to as Calling Line Identification Restriction. Emergency services will most likely be able to show the restricted number using a service called Calling Line Identification Restriction Override, or by using general ANI services.
Caller ID is a simple string of data that can be read and generated very simply by small computer programs and even some inexpensive devices. Although the caller ID information is transmitted in between the first and second 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. Although misleading the phone company by generating ANI code or by other electronic means is very complex, simpler means do exist. Using services like Vonage or Skype, calling from a pay phone, or using a calling card are easy means to fool caller ID.