Caller ID
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- For the protien involved in the synthesis of major histocompatibility complex II, see CLIP (protein).
Caller ID (caller identification or CID, and more properly calling number identification - CNID) 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, CNID is transmitted digitally using Bell 202 modulation between the first and second rings.
The CID is only the calling party number. In the United States, the calling party name is a separate piece of data and must be requested 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.
Fully 99 per cent of the names that could be delivered are available to all central offices in the US. Most carriers, however, are now refusing to retrieve the information for delivery, since it may reside in a non-owned database and would require payment to another provider for the data. The local carrier will then claim the name is "unavailable", or "out of area", or default to a "city, state" response. If a consumer pays for Calling Name delivery, and is promised delivery if the data is available, then the cost of retrieving the data should be irrelevant and consumers should complain to their local dial tone provider about the lack of display of names.
Telemarketing organisations want their names displayed, since having a name displayed actually increases the answer rate for calls. To block a name display involves dialing additinal digits which slows outbound calling and costs additional money.
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 CNID to prevent abuse of the account by unauthorised callers. [citation needed]
The device is helpful for tracing down prank calls and telemarketers. The concept behind caller ID is the value of informed consent; however, it also poses problems for personal privacy.
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[edit] Calling line identification
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 marketing name used in Canada (though customers often call it caller ID). CNID originated with automatic number identification (ANI) in the U.S.
However, CNID and ANI are not 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 telemarketing purposes, the use of alternate Caller ID and alternate Calling Names is very useful and informative to consumers. An outbound dialing company may have one number that would display "American Heart Assn" for calls on Tuesday, and another number that might display "National Republican Com" on Wednesday. Since the databases responsible for changing the names associated with the numbers typically takes weeks to months to make data changes, it is only reasonable for outbound calling centers to have numerous "spoofed" numbers to use to properly identify the customer they are representing at the time.
[edit] History
The first market trial for caller ID and other "TouchStar" services was on July 7, 1984 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 began the first commercial application of caller ID in December 1988 in Memphis, Tennessee and was the first regional Bell to fully deploy the system.
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 ADSI: Analog Display Services Interface
[edit] Operation
In the United States, caller ID information is sent to the called party by the telephone switch as a analog data stream (similar to data passed between two modems), between the first and second ring, while the telephone unit is still on hook. If the telephone call is answered before the second ring, caller ID information is not available. 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.
[edit] Problems
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 U.S. number 1 646 555 1212 may be displayed in the UK as 0646 555 1212, instead of 001 646 555 1212.
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 (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, 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."
- People calling friends often hear, "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.
[edit] Getting around caller ID
[edit] Blocking
Blocking is the common term for preventing the display of a calling number.
Telecommunications regulators vary in their requirements for the use 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 CRTC 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.
In the United States, and possibly elsewhere, blocking does not work when calling toll-free (800, 888, 877 and 866) numbers -- this is because US tollfree subscribers do not receive CNID; they receive ANI instead, and ANI cannot be blocked.
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 PRI.
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.; 1470 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 also route anonymous calls to a service which requires the caller to announce him or herself, 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.
[edit] Hacking
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 payphone, or using a calling card are easy means to fool caller ID.
[edit] Disabling
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. Australia uses 1831. Hong Kong uses 133. Israel uses *43. Other countries and networks may vary. On GSM mobile networks, callers may dial #31# before the number you wish to call to disable it.
[edit] See also
- Calling ID is the identification of whom you are calling, or connecting to, as opposed to caller ID identifying who calls you. Some Centrex telephone systems offer this feature. Similarly, when one Skype user calls another Skype user, the caller can see the other party's details and even an image or photograph they have chosen to represent their identity.
- 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
- List of vertical service codes
