Caller ID The idea of sending the phone number to the customer for identification purposes dates to 1968, when
Ted Paraskevakos introduced the idea of modem-like devices that would send and receive the information over normal voice lines. It sent a small burst of information using the 1200 bit/s
Bell 202 modulation in the time between the first and second rings. The concept was developed through the 1970s and had its first public trial with
Bell Atlantic in 1984 and a follow-up in 1987. The system was widespread in the United States and Canada by the mid-1990s, and spread to most other countries by the end of the decade. It soon became an indispensable system allowing customers to screen calls from
telemarketers. Marketers often provided alternative numbers in the caller ID so returned calls went to an inbound call center instead of the telemarketing firm where the call originated. Unscrupulous users began using this concept, which became known as "spoofing", to hide the true origins of the call to prevent callbacks.
VoIP and SIP The introduction of voice-over-IP (VoIP) systems allowed users to place calls to other users directly through the
internet without ever using the public telephone network. Initially, these systems were proprietary, but over time a series of proposals created the Session Initiation Protocol (SIP), a messaging protocol that contained the information needed to set up a VoIP call between two endpoints. SIP borrowed from existing protocols, including the use of simple headers like "From:" in a format similar to the
SMTP email system. SIP requests are sent to
proxy servers that provide access information for end-users to the caller, which is then used to provide a direct connection between the two endpoints. As the cost of an Internet line with enough
bandwidth to host a given number of simultaneous calls is much less than leasing that number of telephone lines, there was a strong economic benefit for companies to switch to VoIP as well. From the late 1990s a number of new
PBX-like systems emerged that use SIP and VoIP to route calls wherever possible, only exiting to the
public switched telephone network (PSTN) system when required to call a non-VoIP user. A company with several of these systems in separate offices could forward the call to the one closest to the number being dialed, thereby reducing or eliminating
long distance charges. As these systems became popular, new telephony providers emerged that offered centralized SIP routing, allowing both companies and end-users to use VoIP systems to call the service and then route back out to the PSTN. Many of these also allowed incoming calls from conventional phone equipment, providing local or
toll-free numbers for the inbound calls. This allowed users to place calls to and from anywhere with local access for a greatly reduced cost by avoiding the telephone company's own long-distance service. Today, a call may travel for most of its "distance" as a SIP-initiated VoIP call, only exiting to the SS7 PSTN network at the final stages, if ever. As this sort of call became common, even the largest service providers, like
AT&T, began offering SIP/VoIP to their customers. In this case, the caller ID information is taken from the SIP headers, not the provider, and that information is often editable by the end-user.
ID spoofing The opening of the telephone network to VoIP systems resulted in a dramatic lowering in cost for the support of multiple simultaneous phone calls. This was as much of a boon to robocallers as it was to legitimate users. By purchasing commodity
personal computers and running suitable software, a robocaller can make hundreds of simultaneous calls for the cost of a single Internet connection. In the early days of such robocalling, the caller would often attempt to hide their identity by entering false caller ID information into the VoIP software. This had the added advantage to the robocaller of making it impossible for the called user to call back to complain, or even report the call to their provider or government agency like the Federal Trade Commission. Users quickly learned to stop taking calls from obviously faked IDs. and later by using well-known numbers, often government agencies, as part of scams. with an estimated 5.7 billion robocalls in the US placed in October 2019 alone. Estimates for 2020 are 46 billion robocalls in the US alone. ==STIR==