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Short Message Service (SMS) is a communication service standardized in the GSM mobile communication system, using standardized communications protocols allowing the interchange of short text messages between mobile telephone devices. SMS text messaging is the most widely used data application on the planet, with 2.4 billion active users, or 74% of all mobile phone subscribers sending and receiving text messages on their phones. The SMS technology has facilitated the development and growth of text messaging. The connection between the phenomenon of text messaging and the underlying technology is so great that in parts of the world the term "SMS" is used as a synonym for a text message or the act of sending a text message, even when a different protocol is being used.

SMS as used on modern handsets was originally defined as part of the GSM series of standards in 1985 as a means of sending messages of up to 160 characters (including spaces), to and from GSM mobile handsets. Since then, support for the service has expanded to include other mobile technologies such as ANSI CDMA networks and Digital AMPS, as well as satellite and landline networks. Most SMS messages are mobile-to-mobile text messages, though the standard supports other types of broadcast messaging as well.

History

SMS as part of GSM

Initial concept

SMS messages sent monthly in USA (billion)
Matti Makkonen, then of Telecom Finland is credited as the father or inventor of SMS text messaging, and he was awarded the Economist Innnovation Award for this achievement in 2008 . The idea of adding text messaging to the services of mobile users was latent in many communities of mobile communication services at the beginning of the 1980s. The first action plan of the CEPT Group GSM approved in December 1982 requested "The services and facilities offered in the public switched telephone networks and public data networks ...should be available in the mobile system". This target includes the exchange of text messages either directly between mobile stations or the transmission via Message Handling Systems widely in use since the beginning of the 1980s.

The innovation in SMS is indicated by the word Short in Short Message Service. The GSM system is optimized for telephony, since this was identified as its main application. The key idea for SMS was to use this telephony-optimized system and to transport messages on the signaling paths needed to control the telephony traffic during time periods when no signaling traffic existed. In this way unused resources in the system could be used to transport messages without additional cost. However, it was necessary to limit the length of the messages to 128 bytes (later improved to 140 bytes, or 160 7-bit characters), so that the messages could fit into the existing signaling formats. Therefore the service was named “Short Message Service”.

This concept allowed implementing the SMS in every mobile station with additional software routines. A new network element required was a specialised Short Message Service Centre, as well as enhancement to the radio capacity and network transport infrastructure. It needed capacity expansions of course with growing SMS traffic. This concept was instrumental for the implementation of SMS in every mobile station ever produced and in every network from early days on. Hence a large base of SMS capable terminals and networks existed when the users began to utilise the SMS.

Early development

The technical development of SMS was a multi-national collaboration supporting the framework of standards bodies and through these organisations made the technology freely available to the whole world. This is described and supported by evidence in the following sections.

The first proposal for SMS which initiated the development of SMS in the group GSM was made by a contribution of Germany and France into the GSM meeting in February 1985 in Oslo. This proposal was further elaborated in GSM subgroup WP1 Services (Chairman Martine Alvernhe, France Telecom) based on a contribution from Germany. There were also initial discussions in the subgroup WP3 network aspects chaired by Jan Audestad (Telenor). The result was approved by the main group GSM in a document of June 85 which was distributed to industry. The input documents on SMS had been prepared by Friedhelm Hillebrand (Deutsche Telekom) with contributions from Bernard Ghillebaert (France Télécom).

SMS was considered in the main GSM group as a possible service for the new digital cellular system. In GSM document "Services and Facilities to be provided in the GSM System", both mobile originated and mobile terminated short messages appear on the table of GSM teleservices.

The discussions on the GSM services were then concluded in the recommendation GSM 02.03 "TeleServices supported by a GSM PLMN". Here a rudimentary description of the three services was given:

  1. Short message Mobile Terminated (SMS-MT)/ Point-to-Point: the ability of a network to transmit a Short Message to a mobile phone. The message can be sent by phone or by a software application.
  2. Short message Mobile Originated (SMS-MO)/ Point-to-Point: the ability of a network to transmit a Short Message sent by a mobile phone. The message can be sent to a phone or to a software application.
  3. Short message Cell Broadcast.


The material elaborated in GSM and its subgroups WP1 was handed over in spring 1987 to a new GSM body called IDEG (the Implementation of Data and Telematic Services Experts Group), which had its kickoff in May 1987 under the chairmanship of Friedhelm Hillebrand (German Telecom). The technical standard known today was largely created by IDEG (later WP4) as the two recommendations GSM 03.40 (the two point-to-point services merged together) and GSM 03.41 (cell broadcast).

WP4 created a drafting group message handling (DGMH) who was responsible for the specification of SMS. It was chaired by Finn Trosby (Telenor). DGMH had about 5 to 8 participants (Finn Trosby mentions as contributors Alan Cox of Vodafone). The first action plan mentions for the first time the Technical Specification 03.40 “Technical realisation of the Short Message Service”. Responsible editor was Finn Trosby. The first draft of the technical specification was completed in November 1987. A comprehensive description.

The work on the draft specification continued in the following few years, where Kevin Holley of Cellnet (now O2) played a leading role. Besides the completion of the main specification GSM 03.40 also the detailed protocol specifications on the system interfaces needed to be completed[.]

Support in other architectures

The Mobile Application Part (MAP) of the SS7 protocol included support for the transport of Short Messages through the Core Network from its inception. MAP Phase 2 expanded support for SMS by introducing a separate operation code for Mobile Terminated Short Message transport. Since Phase 2, there have been no changes to the Short Message operation packages in MAP, although other operation packages have been enhanced to support CAMEL SMS control.

From 3GPP Releases 99 and 4 onwards, CAMEL Phase 3 introduced the ability for the Intelligent Network to control aspects of the Mobile Originated Short Message Service, while CAMEL Phase 4, as part of 3GPP Release 5 and onwards, provides the IN with the ability to control the Mobile Terminated service. CAMEL allows the gsmSCP to block the submission (MO) or delivery (MT) of Short Messages, route messages to destinations other than that specified by the user, and perform real-time billing for the use of the service. Prior to standardized CAMEL control of the Short Message Service, IN control relied on switch vendor specific extensions to the Intelligent Network Application Part of SS7.

Early implementations

The first SMS message was sent over the Vodafone GSM network in the United Kingdommarker on 3 December 1992, from Neil Papworth of Sema Group (now Airwide Solutions) using a personal computer to Richard Jarvis of Vodafone using an Orbitel 901 handset. The text of the message was "Merry Christmas". The first SMS typed on a GSM phone was sent by Riku Pihkonen, an engineering student at Nokia, in 1993.

The first commercial deployment of a Short Message Service Centre (SMSC) was by Aldiscon (now Acision) with TeliaSonera in Sweden in 1993,, followed by Fleet Call (now Nextel) in the US, Telenor in Norway and BT Cellnet (now O2 UK) later in 1993. All first installations of SMS gateways were for network notifications sent to mobile phones, usually to inform of voice mail messages. The first commercially sold SMS service was offered to consumers, as a person-to-person text messaging service by Radiolinja (now part of Elisa) in 1993. It should be noted that most early GSM mobile phone handsets did not support the ability to send SMS text messages, and Nokia was the only handset manufacturer whose total GSM phone line in 1993 supported user-sending of SMS text messages.

Initial growth was slow, with customers in 1995 sending on average only 0.4 messages per GSM customer per month. One factor in the slow takeup of SMS was that operators were slow to set up charging systems, especially for prepaid subscribers, and eliminate billing fraud which was possible by changing SMSC settings on individual handsets to use the SMSCs of other operators .

Over time, this issue was eliminated by switch-billing instead of billing at the SMSC and by new features within SMSCs to allow blocking of foreign mobile users sending messages through it. By the end of 2000, the average number of messages reached 35 per user per month, and by Christmas Day 2006, over 205m texts were sent in the UK alone.

It is also alleged that the fact that roaming customers, in the early days, rarely received bills for their SMSs after holidays abroad had a boost on text messaging as an alternative to voice calls .

Text messaging outside GSM

SMS was originally designed as part of GSM, but is now available on a wide range of networks, including 3G networks. However, not all text messaging systems use SMS, and some notable alternate implementations of the concept include J-Phone's SkyMail and NTT Docomo's Short Mail, both in Japanmarker. E-mail messaging from phones, as popularized by NTT Docomo's i-mode and the RIM BlackBerry, also typically use standard mail protocols such as SMTP over TCP/IP.

SMS today

In terms of traffic 4.1 Trillion SMS text messages were sent in 2008. Commercially SMS is a massive industry in 2006 worth over 81 billion dollars globally. SMS has an average global price of 0.11 USD while costing providers almost nothing. Mobile networks charge each other so-called interconnect fees of at least £0.03 when connecting between different phone networks

Technical details

GSM

The Short Message Service - Point to Point (SMS-PP) is defined in GSM recommendation 03.40. GSM 03.41 defines the Short Message Service - Cell Broadcast (SMS-CB) which allows messages (advertising, public information, etc.) to be broadcast to all mobile users in a specified geographical area.Messages are sent to a Short Message Service Centre (SMSC) which provides a store-and-forward mechanism. It attempts to send messages to their recipients. If a recipient is not reachable, the SMSC queues the message for later retry. Some SMSCs also provide a "forward and forget" option where transmission is tried only once. Both Mobile Terminated (MT), for messages sent to a mobile handset, and Mobile Originating (MO), for those that are sent from the mobile handset, operations are supported. Message delivery is best effort, so there are no guarantees that a message will actually be delivered to its recipient and delay or complete loss of a message is not uncommon, particularly when sending between networks. Users may request delivery reports to confirm that messages reach the intended recipients, either via the SMS settings of most modern phones, or by prefixing each message with *0# or *N#.

Message size

Transmission of short messages between the SMSC and the handset is done whenever using the Mobile Application Part (MAP) of the SS7 protocol. Messages are sent with the MAP mo- and mt-ForwardSM operations, whose payload length is limited by the constraints of the signaling protocol to precisely 140 octet (140 octets = 140 * 8 bits = 1120 bits). Short messages can be encoded using a variety of alphabets: the default GSM 7-bit alphabet (see GSM 03.38 for details), the 8-bit data alphabet, and the 16-bit UTF-16 alphabet. Depending on which alphabet the subscriber has configured in the handset, this leads to the maximum individual Short Message sizes of 160 7-bit characters, 140 8-bit characters, or 70 16-bit characters (including spaces). Support of the GSM 7-bit alphabet is mandatory for GSM handsets and network elements, but characters in languages such as Arabic, Chinese, Korean, Japanese or Cyrillic alphabet languages (e.g. Russian, Serbian, Bulgarian, etc) must be encoded using the 16-bit UTF-16 character encoding (see Unicode). Routing data and other metadata is additional to the payload size.

Larger content (Concatenated SMS, multipart or segmented SMS or "long sms") can be sent using multiple messages, in which case each message will start with a user data header (UDH) containing segmentation information. Since UDH is inside the payload, the number of characters per segment is lower: 153 for 7-bit encoding, 133 for 8-bit encoding and 67 for 16-bit encoding. The receiving handset is then responsible for reassembling the message and presenting it to the user as one long message. While the standard theoretically permits up to 255 segments, 6 to 8 segment messages are the practical maximum, and long messages are often billed as equivalent to multiple SMS messages. See Concatenated SMS for more information. Some providers have offered length-oriented pricing schemes for SMSs, however, the phenomenon is disappearing.

SMS Gateway providers

SMS gateway providers facilitate the SMS traffic between businesses and mobile subscribers, being mainly responsible for carrying mission-critical messages, SMS for enterprises, content delivery and entertainment services involving SMS, e.g. TV voting. Considering SMS messaging performance and cost, as well as the level of messaging services, SMS gateway providers can be classified as aggregators or SS7 providers.

The aggregator model is based on multiple agreements with mobile carriers to exchange 2-way SMS traffic into and out of the operator’s SMS platform (Short Message Service Centre – SMS-C), also known as local termination model. Aggregators lack direct access into the SS7 protocol, which is the protocol where the SMS messages are exchanged. SMS messages are delivered in the operator’s SMS-C, but not the subscriber’s handset, the SMS-C takes care of further handling of the message through the SS7 network

Another type of SMS gateway provider is based on SS7 connectivity to route SMS messages, also known as international termination model. The advantage of this model is the ability to route data directly through SS7, which gives the provider total control and visibility of the complete path during the SMS routing. This means SMS messages can be sent directly to and from recipients without having to go through the SMS-Centres of other mobile operators. Therefore, it’s possible to avoid delays and message losses, offering full delivery guarantees of messages and optimised routing. This model is particularly efficient when used in mission-critical messaging and SMS used in corporate communications.

Interconnectivity with other networks

Message Service Centres communicate with the Public Land Mobile Network or PSTN via Interworking and Gateway MSCs.

Subscriber-originated messages are transported from a handset to a Service Centre, and may be destined for mobile users, subscribers on a fixed network, or Value-Added Service Providers , also known as application-terminated. Subscriber-terminated messages are transported from the Service Centre to the destination handset, and may originate from mobile users, from fixed network subscribers, or from other sources such as VASPs.

It is also possible, on some carriers, for non-subscribers to send messages to a subscriber's phone using an E-Mail to SMS gateway. Additionally, many carriers, including AT&T, T-Mobile, Sprint, and Verizon Wireless, offer the ability to do this through their respective websites. For example an AT&T subscriber whose phone number was 555-555-5555 would receive e-mails to 5555555555@txt.att.net as text messages. Sending a message this way is free but subject to the normal length limit.

Text enabled fixed-line handsets are required to receive messages in text format. However, messages can be delivered to non-enabled phones using text-to-speech conversion.

Short messages can also be used to send binary content such as ringtones or logos, as well as Over-the-air programming (OTA) or configuration data. Such uses are a vendor-specific extension of the GSM specification and there are multiple competing standards, although Nokia's Smart Messaging is by far the most common. An alternative way for sending such binary content is EMS messaging which is standardised and not dependent on vendors.

Today, SMS is also used for M2M (Machine to Machine) communication. For instance, there is an LED display machine controlled by SMS, and some vehicle tracking companies use SMS for their data transport or telemetry needs. SMS usage for these purposes is slowly being superseded by GPRS services due to their lower overall costs . GPRS is also offered by some smaller telco players as a route of sending SMS text to help reduce the cost of SMS texting internationally.

AT commands

Many mobile and satellite transceiver units support the sending and receiving of SMS using an extended version of the Hayes command set, a specific command-language originally developed for the Hayes Smartmodem 300 baud modem in 1977.

The connection between the terminal equipment and the transceiver can be realized with a serial cable (i.e. USB), a Bluetooth link, an infrared link, etc. Common AT commands include AT+CMGS (send message), AT+CMSS (send message from storage), AT+CMGL (list messages) and AT+CMGR (read message).

However, not all modern devices support receiving of messages if the message storage, for instance the device's internal memory, is not accessible using AT commands.

Premium-rated short messages

Short messages may be used to provide premium rate services to subscribers of a telephone network.

Mobile terminated short messages can be used to deliver digital content such as news alerts, financial information, logos and ring tones. The first premium rate media content delivered via the SMS system, was the world's first paid downloadable ringing tones, as commerically launched by Saunalahti (later Jippii Group, now part of Elisa Group) in 1998. Initially in 1998 only Nokia branded phones could accept this type of external music installment. By 2002 the ringing tone business globally had exceeded one billion dollars of service revenues and in 2008 the 'basic ringing tone' industry was worth nearly 5 billion dollars.

The Value-added service provider (VASP) providing the content submits the message to the mobile operator's SMSC(s) using a TCP/IP protocol such as the short message peer-to-peer protocol (SMPP) or the External Machine Interface . The SMSC delivers the text using the normal Mobile Terminated delivery procedure. The subscribers are charged extra for receiving this premium content, and the amount is typically divided between the mobile network operator and the VASP either through revenue share or a fixed transport fee.

Mobile originated short messages may also be used in a premium-rated manner for services such as televoting. In this case, the VASP providing the service obtains a short code from the telephone network operator, and subscribers send texts to that number. The payouts to the carriers vary by carrier and the percentages paid are greatest on the lowest priced premium SMS services. Most information providers should expect to pay about 45% of the cost of the premium SMS up front to the carrier. The submission of the text to the SMSC is identical to a standard MO Short Message submission, but once the text is at the SMSC, the Service Centre identifies the Short Code as a premium service. The SC will then direct the content of the text message to the VASP, typically using an IP protocol such as SMPP or EMI. Subscribers are charged a premium for the sending of such messages, with the revenue typically shared between the network operator and the VASP. Limitations of short codes include the limitation to national borders (short codes have to be activated in each country where the campaign takes place), as well as being expensive to sign up together with mobile operators.

An alternative to inbound SMS is based on long numbers (international number format, e.g. +44 7624 805000),which can be used in place of short codes for SMS reception in several applications, such as TV voting, product promotions and campaigns. Long numbers are internationally available, as well as enabling businesses to have their own number, rather than short codes which are usually shared across a lot of brands. Additionally, long numbers are non-premium inbound numbers.

SMS in satellite phone networks

All commercial satellite phone networks except ACeS and OptusSat fully support SMS . While early Iridium handsets only support incoming SMS, later models can also send them. The price per message varies for the different networks and is usually between 25 and 50 cents per message. Unlike some mobile phone networks there is no extra charge for sending international SMS or to send one to a different satellite phone network. SMS can sometimes be sent from areas where the signal is too poor to make a voice call.

Satellite phone networks usually have a web-based or email-based SMS portals where one can send free SMS to phones on that particular network.

Vulnerabilities

The Global Service for Mobile communications (GSM), with the greatest worldwide number of users, succumbs to several security vulnerabilities. In the GSM, only the airway traffic between the Mobile Station (MS) and the Base Transceiver Station (BTS) is optionally encrypted with a weak and broken stream cipher (A5/1 or A5/2). The authentication is unilateral and also vulnerable. There are also many other security vulnerabilities and shortcomings. Such vulnerabilities are inherent to the Short Message Service (SMS) as one of the superior and well-tried services with a global availability in the GSM networks. The SMS messaging has some extra security vulnerabilities due to its store-and-forward feature, and the problem of fake SMS that can be conducted via the Internet. When a user is roaming, the SMS content passes through different networks, and perhaps the Internet, and is exposed to various vulnerabilities and attacks. Another concern arises when an adversary gets access to the phone and reads the previous unprotected messages.

In October 2005, researchers from Pennsylvania State Universitymarker published an analysis of vulnerabilities in SMS-capable cellular networks. The researchers speculated that attackers might exploit the open functionality of these networks to disrupt them or cause them to fail, possibly on a nationwide scale.

SMS spoofing

The GSM industry has identified a number of potential fraud attacks on mobile operators that are caused by abuse of SMS messaging services. The most serious of threats is SMS Spoofing. SMS Spoofing occurs when a fraudster manipulates address information in order to impersonate a user that has roamed onto a foreign network and is submitting messages to the home network. Frequently, these messages are addressed to destinations outside the home network – with the home SMSC essentially being “hijacked” to send messages into other networks.

The only 100%-sure way of detecting and blocking spoofed messages is to screen incoming mobile originated messages to verify that the sender is a valid subscriber and that the message is coming from a valid and correct location. This can be implemented by adding an intelligent routing function to the network that can query originating subscriber details from the HLR before the message is submitted for delivery. This kind of intelligent routing function is beyond the capabilities of legacy messaging infrastructure.

Standardization

See also



Details



Related protocols



Related technology



References

  1. GSM Doc 28/85 "Services and Facilities to be provided in the GSM System" rev2, June 1985
  2. LA Times: Why text messages are limited to 160 characters
  3. GSM 03.40, Technical realization of the Short Message Service (SMS).
  4. [1]
  5. see GSM document 02/82 available in the ETSI archive
  6. These Message Handling Systems had been standardised in the ITU, see specifications X.400 series
  7. See GSM document 28/85rev.2 of June 85 and GSM WP1 document 66/86 available in the ETSI archive
  8. See also Friedhelm Hillebrand "GSM and UMTS, the creation of Global Mobile Communication", Wiley 2002, chapters 10 and 16, ISBN 0470 84322 5
  9. GSM document 19/85, available in the ETSI archive
  10. GSM document 28/85r2, available in the ETSI archive
  11. GSM TS 02.03, Teleservices Supported by a GSM Public Land Mobile Network (PLMN).
  12. Document GSM IDEG 79/87r3, available in the ETSI archive
  13. GSM 03.40, WP4 document 152/87, available in the ETSI archive
  14. see See Finn Trosby "SMS, the strange duckling of GSM", published in Telektronikk vol. 3 2004; page 6. Link http://www.telenor.com/telektronikk/volumes/pdf/3.2004/Page_187-194.pdf
  15. MAP phase 1 specification, available from the 3GPP web site.
  16. MAP phase 2 specification, available from the 3GPP web site.
  17. CAMEL Phase 3 specification, available from the 3GPP web site.
  18. CAMEL Phase 4 specification, also available from the 3GPP specification page.
  19. I put the Gr8 in Britain May 2007, London Magazine.
  20. UK hails 10th birthday of SMS, December 2002, The Times of India.
  21. False dawn of the photo phone boom, Jan 2003, The Scotsman.
  22. First commercial deployment of Text Messaging (SMS)
  23. GSM World press release
  24. http://www.dslreports.com/shownews/91379
  25. GSM 03.41, Technical Realization of Short Message Service Cell Broadcast (SMSCB).
  26. Gil Held: "Data over Wireless Networks". page 105-111, 137-138. Wiley, 2001.
  27. 3GPP TS 23.038, Alphabets and language-specific information.
  28. Ian Groves: "Mobile Systems", page 70, 79, 163-166. Chapman & Hall, 1998.
  29. BT trials mobile SMS to voice landline, January 2004, The Register.
  30. [2], September 2006, SMStextnews
  31. SMS Tutorial: Introduction to AT Commands, Basic Commands and Extended Commands
  32. An Analysis of Vulnerabilities in SMS-Capable Cellular Networks:Exploiting Open Functionality in SMS-Capable Cellular Networks (September 2, 2005)
  33. An overview on how to stop SMS Spoofing in mobile operator networks (September 9, 2008)


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