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SMS as part of GSM

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".[3] 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.[4]

The innovation in SMS is indicated by the word Short in Short Message Service. But why should the message length be limited to 160 characters in a situation where a service with an unlimited message length was available (e.g. a service using a Message Handling System)? The GSM system is optimised for telephony, since this was identified as its main application. The key idea for SMS was to use this telephony-optimised system and to transport messages on the signalling paths needed to control the telephony traffic during time periods when no signalling traffic existed. In this way unused resources in the system could be used to transport messages without additional cost. But it was necessary to limit the length of the messages to 128 bytes (later improved to 160 characters), so that the messages could fit into the existing signalling formats. Therefore the service was named “Short Message Service”.

This concept allowed implementing the SMS in every mobile station just by an additional software routine without incremental cost per unit. Also the implementation in the networks required just software without incremental cost. The only new network element was a specialised Short Message Service Centre for a whole countrywide network. 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.[5]

No individual expert or company can claim to be the ‘father’ or ‘creator’ of the SMS. The GSM project as a whole was indeed a multi-national collaboration at its best. Therefore the responsibility for the SMS innovation is not with a single person but with a network of closely cooperating persons who has created this innovation. They did this with the supporting framework of Standard 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.[6]

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[7]. This proposal was further elaborated in GSM subgroup WP1 Services (Chairman Martine Alvernhe, France Teelecom) based on a contribution from Germany. There were also initial discussions in the subgroup WP3 network aspects chaired by Jan Audestat (Telenor). The result was approved by the main group GSM in a document of June 85 which was distributed to industry.[8] The input documents on SMS had been prepared by Friedhelm Hillebrand (German Telecom) with contributions from Bernard Ghillebaert (France Telecom).

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",[1] 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".[9] 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[10] 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 of November 1987[11] ().

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.

The Mobile Application Part (MAP) of the SS7 protocol included support for the transport of Short Messages through the Core Network from its inception.[12] MAP Phase 2 expanded support for SMS by introducing a separate operation code for Mobile Terminated Short Message transport.[13] 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 (IN) to control aspects of the Mobile Originated Short Message Service,[14] while CAMEL Phase 4, as part of 3GPP Release 5 and onwards, provides the IN with the ability to control the Mobile Terminated service.[15] 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 (INAP) of SS7.

The first SMS message[16] was sent over the Vodafone GSM network in the United Kingdom 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".[17] The first SMS typed on a GSM phone is claimed to have been sent by Riku Pihkonen, an engineering student at Nokia, in 1993.[18]

The first commercial deployment of a Short Message Service Centre (SMSC) was by Aldiscon (now Acision) with Telia in Sweden in 1993,[19], followed by Fleet Call (now Nextel)[citation needed] in the US, Telenor in Norway[citation needed] and BT Cellnet (now O2 UK)[citation needed] later in 1993.

Initial growth was slow, with customers in 1995 sending on average only 0.4 messages per GSM customer per month.[20] 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[citation needed].

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,[20] and by Christmas Day 2006, over 205m texts were sent in the UK alone.[21]

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[citation needed].

[edit] 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 Japan. 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.

[edit] SMS today

Commercially SMS is a massive industry in 2006 worth over 81 billion dollars globally.[22] SMS has an average global price of 0.11 USD and maintains a near 90% profit margin.

[edit] Technical details

[edit] GSM

The Short Message Service - Point to Point (SMS-PP) is defined in GSM recommendation 03.40.[2] 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.[23] 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.[24] 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 choose to request delivery reports (simply add *0# or *N# to the beginning of your text message), which can provide positive confirmation that the message has reached the intended recipient.

GSM 03.38

x0 x1 x2 x3 x4 x5 x6 x7 x8 x9 xA xB xC xD xE xF
0x @ £ $ ¥ è é ù ì ò Ç LF Ø ø CR Å å
1x Δ _ Φ Γ Λ Ω Π Ψ Σ Θ Ξ ESC Æ æ ß É
2x SP ! " # ¤ % & ' ( ) * + , - . /
3x 0 1 2 3 4 5 6 7 8 9 : ; < = > ?
4x ¡ A B C D E F G H I J K L M N O
5x P Q R S T U V W X Y Z Ä Ö Ñ Ü §
6x ¿ a b c d e f g h i j k l m n o
7x p q r s t u v w x y z ä ö ñ ü à
1B 0x


1B 1x


1B 2x

{ }

1B 3x

[ ~ ]
1B 4x |

1B 5x

1B 6x

1B 7x

[edit] Message size

Transmission of short messages between the SMSC and the handset is done 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 signalling protocol to precisely 140 octets (140 octets = 140 * 8 bits = 1120 bits). Short messages can be encoded using a variety of alphabets: the default GSM 7-bit alphabet (shown above), the 8-bit data alphabet, and the 16-bit UTF-16/UCS-2 alphabet.[25] 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,[25] but characters in languages such as Arabic, Chinese, Korean, Japanese or Cyrillic alphabet languages (e.g. Russian) must be encoded using the 16-bit UCS-2 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, 134 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,[26] 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.

[edit] SMS Compression

An Indian startup myMobile Ergonomics has introduced on phone SMS Compression in its products CleverTexting and Panini Keypad in which they offer an increase in the capacity of the SMS by 40% and 350% respectively. This is done through an application on the phone with its own compression and decompression routines which uses the SMS as a transport layer.

[edit] 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.

[edit] Interconnectivity with other networks

Message Service Centres communicate with the Public Land Mobile Network (PLMN) 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 (VASPs), 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 E-Mail. AT&T, T-Mobile[27], Sprint[28], Verizon Wireless[29] offer the ability to do this through their websites mail server. For example an AT&T subscriber whose phone number was 555-555-5555 would receive e-mails to as text messages. Sending a message this way is free but subject to the normal length limit. Primus Canada is one carrier that lacks this feature.

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.[30]

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 are slowly being superseded by GPRS services due to their lower overall costs[citation needed].

[edit] AT commands

Many mobile and satellite transceiver units support the sending and receiving of SMS using an extended version of the Hayes command set. 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).[31]

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.

[edit] 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 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 (EMI). 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.

See also: Reverse SMS billing and Mobile search

[edit] SMS in satellite phone networks

All commercial Satellite phone networks except ACeS and OptusSat fully support SMS[citation needed]. 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.

[edit] 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[32]. Such vulnerabilities are inherited 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 that exposes it to various vulnerabilities and attacks. Another concern is arisen when an adversary gets access to the phone and reads the previous unprotected messages[33].
In October 2005, researchers from Pennsylvania State University published an analysis of vulnerabilities in SMS-capable cellular networks.[34] 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 these 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.[35]

[edit] See also

[edit] Details

[edit] Related protocols

[edit] Related technology

[edit] References

  1. ^ a b GSM Doc 28/85 "Services and Facilities to be provided in the GSM System" rev2, June 1985
  2. ^ a b GSM 03.40, Technical realization of the Short Message Service (SMS).
  3. ^ see GSM document 02/82 available in the ETSI archive
  4. ^ These Message Handling Systems had been standardised in the ITU, see specifications X.400 series
  5. ^ See GSM document 28/85rev.2 of June 85 and GSM WP1 document 66/86 available in the ETSI archive
  6. ^ See also Friedhelm Hillebrand "GSM and UMTS, the creation of Global Mobile Communication", Wiley 2002, chapters 10 and 16, ISBN 0470 84322 5
  7. ^ GSM document 19/85, available in the ETSI archive
  8. ^ GSM document 28/85r2, available in the ETSI archive
  9. ^ GSM TS 02.03, Teleservices Supported by a GSM Public Land Mobile Network (PLMN).
  10. ^ Document GSM IDEG 79/87r3, available in the ETSI archive
  11. ^ GSM 03.40, WP4 document 152/87, available in the ETSI archive
  12. ^ MAP phase 1 specification, available from the 3GPP web site.
  13. ^ MAP phase 2 specification, available from the 3GPP web site.
  14. ^ CAMEL Phase 3 specification, available from the 3GPP web site.
  15. ^ CAMEL Phase 4 specification, also available from the 3GPP specification page.
  16. ^ I put the Gr8 in Britain May 2007, London Magazine.
  17. ^ UK hails 10th birthday of SMS, December 2002, The Times of India.
  18. ^ False dawn of the photo phone boom, Jan 2003, The Scotsman.
  19. ^ First commercial deployment of Text Messaging (SMS)
  20. ^ a b GSM World press release
  21. ^ Crystal, David (2008-07-05). "2b or not 2b?". Guardian Unlimited.,,2289259,00.html. Retrieved on 2008-07-08.
  22. ^ ITU Internet Report 2006:, Chapter 3PDF (451 KiB)
  23. ^ GSM 03.41, Technical Realization of Short Message Service Cell Broadcast (SMSCB).
  24. ^ Gil Held: "Data over Wireless Networks". page 105-111, 137-138. Wiley, 2001.
  25. ^ a b 3GPP TS 23.038, Alphabets and language-specific information.
  26. ^ Ian Groves: "Mobile Systems", page 70, 79, 163-166. Chapman & Hall, 1998.
  27. ^ "t-zones text messaging: send and receive messages with mobile text messaging". Retrieved on 2008-09-18.
  28. ^ "Support - How do I compose and send a text message to a Sprint or Nextel customer from email?". Retrieved on 2008-09-18.
  29. ^ "Answers to FAQs - Verizon Wireless Support". Retrieved on 2008-09-18.
  30. ^ BT trials mobile SMS to voice landline, January 2004, The Register.
  31. ^ SMS Tutorial: Introduction to AT Commands, Basic Commands and Extended Commands
  32. ^ Mohsen Toorani, and Ali Asghar Beheshti Shirazi, (September 2008). Solutions to the GSM Security Weaknesses,Proceedings of the Second IEEE International Conference on Next Generation Mobile Applications, Services, and Technologies (NGMAST2008), pages=576-581, University of Glamorgan, Cardiff, UK.
  33. ^ Mohsen Toorani, and Ali Asghar Beheshti Shirazi, (July 2008). SSMS - A Secure SMS Messaging Protocol for the M-Payment Systems, Proceedings of the 13th IEEE Symposium on Computers and Communications (ISCC'08), pages=700-705, IEEE ComSoc, Marrakesh, Morocco.
  34. ^ An Analysis of Vulnerabilities in SMS-Capable Cellular Networks:Exploiting Open Functionality in SMS-Capable Cellular Networks (September 2, 2005)
  35. ^ An overview on how to stop SMS Spoofing in mobile operator networks (September 9, 2008)

[edit] External links

Saturday, February 14, 2009

Short message service

Short Message Service (SMS) is a communication service standardised in the GSM mobile communication system, using standardised 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.[citation needed] 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[1] as a means of sending messages of up to 160 characters (including spaces), to and from GSM mobile handsets.[2] Since then, support for the service has expanded to include alternative mobile standards such as ANSI CDMA networks and Digital AMPS, as well as satellite and landline networks.[citation needed] Most SMS messages are mobile-to-mobile text messages, though the standard supports other types of broadcast messaging as well.