SMS
Short Message Service (SMS) is a store-and-forward text messaging protocol standardized for transmission of brief alphanumeric messages, typically up to 160 characters in length using 7-bit GSM encoding, between mobile devices over cellular networks such as GSM.[1][2] Developed in the early 1980s by engineers including Friedhelm Hillebrand, who proposed the core concept of short personal messaging during GSM standardization efforts by the European Conference of Postal and Telecommunications Administrations (CEPT), SMS enables asynchronous communication without requiring both parties to be online simultaneously, distinguishing it from circuit-switched voice calls.[3] The first operational SMS message, "Merry Christmas," was sent on December 3, 1992, by engineer Neil Papworth from a computer to a Vodafone Orbitel 901 handset via the UK's public land mobile network, marking the practical debut of the service shortly after its formal specification in GSM phase 1 standards.[4][5] SMS rapidly proliferated in the 1990s and 2000s as mobile penetration grew, evolving from a niche notification tool—initially for voicemail alerts and network updates—to a primary interpersonal and commercial medium due to its low bandwidth demands and universal compatibility across carriers without needing internet access.[6] By design, messages are routed via SMS centers (SMSCs) that queue and deliver payloads even if the recipient device is temporarily unavailable, supporting global interoperability under protocols like those in 3GPP TS 23.040 for technical realization.[7] Adoption peaked with cultural phenomena like widespread youth texting in Europe and Asia, where prepaid plans incentivized volume over voice minutes, though vulnerabilities to spoofing and phishing emerged as usage scaled, prompting regulatory scrutiny on consent and security.[8] As of recent estimates, approximately 23 billion SMS messages are exchanged daily worldwide, underscoring its enduring role in two-factor authentication, alerts, and regions with limited data infrastructure despite competition from IP-based alternatives.[9]History
Origins and Initial Development
The concept of Short Message Service (SMS) emerged in the early 1980s as part of efforts to standardize mobile telecommunications in Europe through the Global System for Mobile Communications (GSM). In 1982, the Conférence Européenne des Administrations des Postes et des Télécommunications (CEPT) established the GSM group to develop a pan-European digital cellular network, addressing fragmentation in analog systems. Friedhelm Hillebrand, a German telecommunications engineer, and Bernard Ghillebaert, a French counterpart, proposed the SMS idea in 1984 during Franco-German collaboration within the GSM working group, envisioning a simple, asynchronous text messaging system that could utilize existing signaling channels without requiring dedicated voice circuits.[10][11] Hillebrand's contributions were instrumental in defining SMS parameters; to determine feasible message length, he manually typed common phrases and sentences on a typewriter, counting characters until they exceeded the capacity of GSM's available signaling bits, settling on a 160-character alphanumeric limit that balanced usability with efficient use of the network's control channel. This limit ensured SMS could operate as a low-bandwidth, store-and-forward service routed via a Short Message Service Center (SMSC), independent of call setup. The GSM memorandum of understanding, signed in 1987 by 13 European nations, formalized SMS within the standard's Phase 1 specifications, though implementation required further protocol refinements by ETSI (European Telecommunications Standards Institute).[11][12] Initial development progressed through prototypes in the late 1980s and early 1990s, focusing on integration with GSM's SS7 signaling system for message routing. The first functional demonstration occurred on December 3, 1992, when 22-year-old engineer Neil Papworth, working for Sema Group (a Vodafone contractor), transmitted the message "Merry Christmas" from a personal computer via the Vodafone network to an Orbitel 901 handset owned by colleague Richard Jarvis in the United Kingdom. This test validated end-to-end delivery using a development SMSC, confirming SMS's viability on live GSM infrastructure before commercial rollout.[13][14]Standardization and Early Deployments
The Short Message Service (SMS) was standardized as an integral component of the Global System for Mobile Communications (GSM) specifications developed by the European Telecommunications Standards Institute (ETSI). The primary technical specification for point-to-point SMS, GSM 03.40, outlined the protocol for message transfer between mobile stations and service centers within the GSM public land mobile network (PLMN), including procedures for submission, delivery, and status reporting.[15] Complementary standards, such as GSM 03.38, defined the default 7-bit alphabet for character encoding, enabling up to 160 characters per message in the initial format.[16] These specifications were finalized in the early 1990s as part of GSM Phase 1, building on earlier conceptual work from the late 1980s to ensure interoperability across European networks amid the shift from analog to digital cellular systems.[1] The first operational SMS transmission occurred on December 3, 1992, over the Vodafone GSM network in the United Kingdom, when engineer Neil Papworth sent the message "Merry Christmas" from a personal computer to the Orbitel 901 handset of colleague Richard Jarvis.[13] This test demonstrated the feasibility of SMS using the existing GSM signaling channels (specifically, the control channel for out-of-band delivery during idle periods), without requiring dedicated data infrastructure.[17] Initial deployments were confined to early GSM operators, as SMS relied on the Short Message Service Center (SMSC) to store and forward messages when recipients were unavailable, a mechanism specified in GSM 03.40 to handle network congestion and mobility.[15] Commercial rollout began in 1993, with Aldiscon providing the first SMS service to Telia in Sweden, followed by deployments in networks such as Fleet Call (later AirTouch) in the United States and Telenor in Norway.[18] These early systems supported basic person-to-person messaging and rudimentary application-to-person alerts, such as network notifications, but adoption was gradual due to limited handset compatibility—initially only Nokia and similar GSM devices with numeric keypads for input—and the absence of cross-network interoperability until later enhancements.[19] By mid-1993, SMS volumes remained low, with operators like Radiolinja in Finland integrating it into their 1991-launched GSM service for paging-like notifications, marking the transition from experimental to viable consumer feature in digital mobile ecosystems.[10]Rapid Growth and Peak Adoption
Following early deployments in GSM networks, SMS usage accelerated dramatically in the late 1990s and early 2000s as mobile phone penetration expanded and per-message costs declined, particularly in Europe and Asia where prepaid plans made it accessible to younger users. By 2002, global SMS traffic exceeded 250 billion messages annually, reflecting widespread adoption on feature phones equipped with predictive text input like T9.[20] In the United States, average monthly texts per user rose from 35 in 2000 to surpassing voice calls by 2007, driven by network expansions and cultural shifts toward asynchronous communication.[20] This growth intensified through the mid-2000s, fueled by viral phenomena such as SMS-based voting in events like Eurovision in 2002 and the popularity of character-limited novels in Japan by 2003, which normalized texting as a social medium. Worldwide volumes reached 6.1 trillion messages in 2010, equivalent to 200,000 per minute, before climbing 44% to 7.4 trillion in 2011.[20][21] Peak adoption occurred around 2011-2012, when SMS dominated person-to-person mobile messaging globally, with daily volumes approaching 23 billion in some estimates, prior to the rise of internet-based alternatives like WhatsApp (launched 2009) and iMessage (2011) that offered richer media without carrier fees.[20] In the U.S., total messages hit 2.4 trillion in 2011, marking the zenith before smartphone data plans shifted preferences.[22] While application-to-person services continued growing, peer-to-peer SMS volumes began declining post-2012 as over-the-top apps proliferated on 3G/4G networks.[23]Modern Challenges and Shifts
In developed markets, person-to-person SMS usage has declined sharply since the early 2010s due to the rise of over-the-top (OTT) messaging applications like WhatsApp and iMessage, which provide richer media support, end-to-end encryption, and internet-based delivery without carrier fees. Globally, enterprise SMS volumes for one-time passwords (OTPs) and marketing have also decreased in high-income regions, though outliers persist in the United States where SMS remains a key channel for business communications.[24] Despite this, an estimated 5.9 billion people worldwide were projected to send or receive SMS messages by 2025, with sustained relevance in developing countries reliant on feature phones and limited data infrastructure.[25] Security vulnerabilities pose significant modern challenges, as SMS lacks inherent end-to-end encryption, making it susceptible to interception, SIM swapping attacks, and impersonation. Smishing—phishing via SMS—has surged, with 76% of businesses reporting incidents in the past year and a 328% increase in attacks, often exploiting trust in text alerts for financial scams that cost U.S. consumers $470 million in 2024 alone.[26][27] Scammers increasingly use "SMS blasters" capable of sending up to 100,000 fraudulent texts per hour by spoofing legitimate numbers, evading traditional filters.[28] The ongoing sunset of 2G and 3G networks worldwide disrupts SMS reliability, as these legacy systems underpin basic messaging for billions of devices, including feature phones and IoT endpoints. Shutdowns, accelerated since 2022 in regions like Europe and North America, force migration to 4G/LTE, where SMS fallback may fail without proper operator policies, potentially rendering older handsets unable to send or receive texts.[29] Over 50% of cellular-connected IoT devices risk disconnection without upgrades, impacting sectors like utilities and tracking that depend on SMS alerts.[30] A key shift is the transition toward Rich Communication Services (RCS), an IP-based protocol enhancing SMS with features like high-resolution media, read receipts, and group chats, while maintaining fallback to SMS for interoperability. Following Apple's RCS support rollout in iOS 18 during 2024, U.S. daily RCS messages reached 1 billion by mid-2025, signaling accelerated adoption among Android and iOS users.[31] However, RCS deployment remains uneven globally, with the market valued at approximately $3 billion in 2025 but limited by carrier fragmentation and incomplete end-to-end encryption in many implementations.[32][33] This evolution addresses SMS constraints but introduces higher costs and dependency on data connectivity, preserving SMS's role in low-bandwidth scenarios like emergency notifications and two-factor authentication despite its risks.[34]Technical Foundations
Protocol Mechanics in GSM Networks
The Short Message Service (SMS) in Global System for Mobile Communications (GSM) networks relies on the Signaling System No. 7 (SS7) for out-of-band control signaling, enabling asynchronous text message transfer independent of voice circuits.[35] The protocol mechanics are governed by GSM Technical Specification 03.40, which outlines point-to-point SMS procedures, including mobile-originated (MO) and mobile-terminated (MT) paths, using Transfer Protocol Data Units (TPDUs) such as SMS-SUBMIT, SMS-DELIVER, and associated acknowledgments.[15] Key network elements include the Mobile Station (MS), Base Station Subsystem (BSS), Mobile Switching Center (MSC), Visitor Location Register (VLR), Home Location Register (HLR), and Short Message Service Center (SMSC), with the SS7 stack—comprising Message Transfer Part (MTP), Signaling Connection Control Part (SCCP), Transaction Capabilities Application Part (TCAP), and Mobile Application Part (MAP)—facilitating inter-entity communication.[36] SMS employs a layered architecture for protocol handling: the SMS Application Layer (SM-AL) manages user data and service elements; the Transfer Layer (SM-TL) encodes/decodes Protocol Data Units (PDUs); the Relay Layer (SM-RL) supports relay functions; and lower layers interface with SS7 for transport.[36] MAP operations, such as MO-forwardSM and MT-forwardSM, carry SMS payloads between the MSC and SMSC, while routing queries use SendRoutingInfoForSM to the HLR.[37] The SMSC acts as a store-and-forward node, queuing undeliverable messages and retrying delivery based on network status updates from the HLR.[38] In the MO procedure, the sending MS transmits an SMS-SUBMIT TPDU over the GSM radio interface (using LAPDm and RR layers) to the BSS, which relays it to the serving MSC via the BSS Application Part (BSSAP).[38] The MSC invokes the MAP MO-forwardSM operation over SS7 to deliver the message to the SMSC, which acknowledges receipt with an SMS-SUBMIT-REPORT to the MS, confirming submission success regardless of final delivery.[38] The SMSC then initiates delivery to the recipient by querying the HLR with SendRoutingInfoForSM, obtaining the recipient's IMSI, serving MSC address, and VLR details; if the recipient is unreachable, the HLR may trigger an AlertServiceCentre MAP message upon availability.[38] For MT procedures, an external entity or another SMSC submits the message to the originating SMSC, which performs the HLR routing query as in MO delivery.[38] The SMSC then sends MT-forwardSM over SS7 to the recipient's serving MSC/VLR, which pages the MS if idle, delivers the SMS-DELIVER TPDU over the air interface, and receives an acknowledgment from the MS.[38] The MSC/VLR returns an MT-forwardSM acknowledgment to the SMSC, which may issue an SMS-STATUS-REPORT to the original sender indicating delivery status; error conditions, such as subscriber busy or network congestion, trigger MAP error responses like System-Failure or Absent-Subscriber.[15] Roaming scenarios involve additional VLR-HLR interactions via MAP ProvideSubscriberInfo to validate subscriber presence before paging.[38]Message Structure and Constraints
SMS messages are transmitted in the form of Protocol Data Units (PDUs), which include a Service Centre Address (SCA) specifying the SMS Centre and a Transfer Protocol Data Unit (TPDU) containing the message payload and metadata.[39] The TPDU format varies between SMS-SUBMIT for messages sent from a mobile station to the service centre and SMS-DELIVER for messages delivered from the service centre to a mobile station.[39] Key TPDU elements include the TP-Message-Type-Indicator (TP-MTI, 2 bits indicating message type), TP-Protocol-Identifier (TP-PID, octet for application or protocol ID), TP-Data-Coding-Scheme (TP-DCS, octet defining encoding and alphabet), TP-User-Data-Length (TP-UDL, specifying length in octets or septets), and TP-User-Data (TP-UD, the message content).[39] SMS-SUBMIT additionally features TP-Destination-Address (TP-DA, 2-12 octets for recipient number), TP-Message-Reference (TP-MR, unique integer), and optional TP-Validity-Period (TP-VP, 0-7 octets for expiration).[39] SMS-DELIVER includes TP-Originating-Address (TP-OA, 2-12 octets for sender) and TP-Service-Centre-Time-Stamp (TP-SCTS, 7 octets for receipt timestamp).[39] Flags such as TP-UDHI (User Data Header Indicator, 1 bit for optional headers like concatenation) and TP-SRR (Status Report Request, 1 bit) modify behavior.[39] The TP-DCS determines the alphabet and encoding, with support for GSM 7-bit default alphabet (per 3GPP TS 23.038), 8-bit binary data, and UCS2 (16-bit Unicode).[39][40] The GSM 7-bit default alphabet encodes 128 characters using 7 bits each, enabling packing into octets for efficiency.[40] TP-UD is constrained to 140 octets maximum for a single message, with effective character limits varying by encoding; presence of a user data header (e.g., for concatenation) reduces this by 6 octets.[39] The following table outlines limits without headers:| Encoding | Max TP-UD Length | Max Characters |
|---|---|---|
| GSM 7-bit | 140 octets (160 septets) | 160 |
| 8-bit data | 140 octets | 140 bytes |
| UCS2 | 140 octets | 70 |