Editing Caller ID (section)

==Operation==
In the United States and Canada, caller ID information is sent to the called party by the [[telephone switch]] as an analog data stream (similar to data passed between two [[modem]]s), using Bell 202 modulation between the first and second rings, while the telephone unit is still on hook.  If the telephone call is answered too quickly after the first ring, caller ID information may not be transmitted to the recipient. Also, in the United States and Canada a caller may block the display of the number they are calling from by dialling *67 before dialling the phone number.<ref>{{Cite web |url=https://www.lifewire.com/hide-your-number-with-star-67-4154833 |title=How to Hide Your Number With *67 |access-date=February 29, 2020 |archive-date=February 29, 2020 |archive-url=https://web.archive.org/web/20200229172324/https://www.lifewire.com/hide-your-number-with-star-67-4154833 |url-status=live }}</ref> This will not work when dialling a toll-free number, where the receiver of the call pays for the call, or when 911 emergency calls are made. Dialling this code does not stop your number from being sent to the terminating central office, only from being displayed. The number can still be "collected" in the case of harassing phone calls.

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.

In general, CID as transmitted from the origin of the call is only the calling party's full phone number (including area code, and including international access code and country code if it's an international call). 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.  A query (dip) with [[Signalling System 7]] (SS7) query may be initiated by the called party's central office to retrieve the information for Calling Name delivery to the caller ID equipment at the subscriber's location, if the caller's name has not already been associated with the calling party's line at the originating central office.  Canadian systems (depending on the provider) using CCS7 automatically (but not in all cases) 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. This CNAM dip fee is very small – less than a penny per call. AT&T starts their negotiations for CNAM dip fees at about $.004 per lookup. OpenCNAM fees are a bit more expensive, up to $.0048 per lookup. 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, particularly for wireless callers.  For toll-free numbers, they may report a string such as {{mono|TOLLFREE NUMBER}} if the name is not available in a database.

[[Smartphone]]s can use a third-party [[mobile app]] to do the name lookup in a third-party database.

=== Other signaling methods ===
Not all types of caller identification use 202-type modulation, nor do all systems send the information between the first and second ring. As a result, not all caller ID devices are compatible from country to country or within the same country, even though the basic phone system is the same.

Besides Bell, the most common on-hook caller ID standard is European standard ETSI EN 300 659-1, which defines three caller ID ("PSTN display") protocols:<ref name="300.659.1">{{cite web |title=Draft ETSI EN 300 659-1 V1.3.1 (2000-09) Access and Terminals (AT); Analogue access to the Public Switched Telephone Network (PSTN); Subscriber line protocol over the local loop for display (and related) services; Part 1: On-hook data transmission |url=https://www.etsi.org/deliver/etsi_en/300600_300699/30065901/01.03.01_40/en_30065901v010301o.pdf |website=etsi.org |access-date=20 November 2023 |date=September 2000 |archive-date=November 20, 2023 |archive-url=https://web.archive.org/web/20231120030545/https://www.etsi.org/deliver/etsi_en/300600_300699/30065901/01.03.01_40/en_30065901v010301o.pdf |url-status=live }}</ref>
* [[ITU-T V.23|V.23]] mode 2 (a different FSK protocol; without using the 75-baud reverse channel), after a normal ring.
* V.23 mode 2, before the ring, but after a special alerting signal (a dual-tone, a short ring "pulse", or a [[line reversal]] followed by a dual-tone).
* A [[DTMF]] signalling using the 16 standard dialing tones.

EN 300 659-2 expands the standard to "on-hook" (call-waiting) situations, still using V.23.<ref>{{cite web |title=ETS 300 659-2 Public Switched Telephone Network (PSTN); Subscriber line protocol over the local loop for display (and related) services; Part 2: Off-hook data transmission |url=http://affon.narod.ru/Phoneline/300659-2.pdf |date=September 1997 |access-date=November 20, 2023 |archive-date=November 20, 2023 |archive-url=https://web.archive.org/web/20231120030545/http://affon.narod.ru/Phoneline/300659-2.pdf |url-status=live }}</ref>

The Chinese caller ID standard of 1997 is largely similar to Bellcore (with the "type II" extension).<ref>{{cite web |title=电话主叫识别信息传送及显示功能的技术要求和测试方法 |url=https://kosen.com.cn/news/download/cid/FSK.pdf |date=1997-12-03 |access-date=November 20, 2023 |archive-date=November 20, 2023 |archive-url=https://web.archive.org/web/20231120030546/https://kosen.com.cn/news/download/cid/FSK.pdf |url-status=live }}</ref>