Editing SMS (section)

== Technical details ==

=== GSM ===
{{Main|Short message service technical realisation (GSM)}}
The ''Short Message Service—Point to Point (SMS-PP)''—was originally defined in GSM recommendation 03.40, which is now maintained in [[3GPP]] as TS 23.040.<ref name="GSM 03.40">{{cite web|url=https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=141|title=Technical realization of the Short Message Service (SMS)|id=GSM TS 03.40|access-date=3 December 2022|archive-date=3 December 2022|archive-url=https://web.archive.org/web/20221203215922/https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=141|url-status=live}}</ref><ref>{{cite web|url=https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=747|title=Technical realization of the Short Message Service (SMS)|id=3GPP TS 23.040|access-date=3 December 2022|archive-date=7 December 2022|archive-url=https://web.archive.org/web/20221207054608/https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=747|url-status=live}}</ref> GSM 03.41 (now 3GPP TS 23.041) 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.<ref name="GSM 03.41">{{cite web|url=https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=142|title=Technical Realization of Short Message Service Cell Broadcast (SMSCB)|id=GSM TS 03.41|access-date=3 December 2022|archive-date=3 December 2022|archive-url=https://web.archive.org/web/20221203215908/https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=142|url-status=live}}</ref><ref>{{cite web|url=https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=748|title=Technical realization of Cell Broadcast Service (CBS)|id=3GPP TS 23.041|access-date=3 December 2022|archive-date=3 December 2022|archive-url=https://web.archive.org/web/20221203215908/https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=748|url-status=live}}</ref> [[Cell broadcast]] is the technology behind [[Wireless Emergency Alerts]] in the US which is used for public safety messages and AMBER alerts,<ref>{{cite web|url=http://www.fcc.gov/guides/wireless-emergency-alerts-wea |title=Wireless Emergency Alerts (WEA) |date=6 May 2014 |publisher=FCC.gov |access-date=2015-07-15}}</ref><ref>{{cite web |url=http://www.eena.org/ressource/static/files/2011_11_17_one2many.pdf |title=Cell Broadcast ; One2many |publisher=Eena.org |access-date=2015-07-15 |archive-date=2015-09-23 |archive-url=https://web.archive.org/web/20150923234130/http://www.eena.org/ressource/static/files/2011_11_17_one2many.pdf |url-status=dead }}</ref> and similar public safety messages in [[Cell broadcast#Public warning implementations|other countries]]. These messages are similar to SMS messages.

Messages are sent to a [[short message service center]] (SMSC), which provides a "[[store and forward]]" mechanism. It attempts to send messages to the SMSC's recipients. If a recipient is not reachable, the SMSC queues the message for later retry.<ref>Gil Held: "Data over Wireless Networks." pages 105–11, 137–38. Wiley, 2001.</ref> 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 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, but delay or complete loss of a message is uncommon, typically affecting less than 5 percent of messages.<ref>{{citation |url=https://cs.uwaterloo.ca/research/tr/2007/CS-2007-42.pdf |title=Design and Implementation of a Short Message Service Data Channel for Mobile Systems |last=Oliver |first=Earl |access-date=March 14, 2022 |archive-date=January 26, 2022 |archive-url=https://web.archive.org/web/20220126180516/https://cs.uwaterloo.ca/research/tr/2007/CS-2007-42.pdf |url-status=live }}</ref> Some providers allow users to request delivery reports, either via the SMS settings of most modern phones, or by prefixing each message with *0#.<ref>{{Cite news|date=December 9, 2018|title=Text Message Tips (not sent or received)|url=https://community.o2.co.uk/t5/How-to-Guides/Text-Message-Tips-not-sent-or-received/ba-p/1179723|access-date=September 28, 2021|website=community.o2.co.uk|language=en|archive-date=September 28, 2021|archive-url=https://web.archive.org/web/20210928142837/https://community.o2.co.uk/t5/How-to-Guides/Text-Message-Tips-not-sent-or-received/ba-p/1179723|url-status=live}}</ref>

=== Message size ===
Transmission of short messages between the SMSC and the handset is done whenever using the [[Mobile Application Part]] (MAP) of the [[Signaling System 7|SS7]] protocol.<ref>{{cite web|url=http://services.eng.uts.edu.au/userpages/kumbes/public_html/ra/sms/|access-date=October 5, 2013 |last=Amri |first=Kuross |title=Communication Networks |archive-url=https://web.archive.org/web/20160511143408/http://services.eng.uts.edu.au/userpages/kumbes/public%5Fhtml/ra/sms/|archive-date=May 11, 2016 |url-status=dead}}</ref>  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 [[byte]]s (140 bytes × 8 bits / byte = 1120 bits).

Short messages can be encoded using a variety of alphabets: the default [[GSM 03.38|GSM 7-bit alphabet]], [[GSM 03.38#GSM 8 bit data encoding|the 8-bit data alphabet]], and the 16-bit [[UCS-2]] or [[UTF-16]] alphabets.<ref>{{cite web|url=https://www.twilio.com/engineering/2012/11/08/adventures-in-unicode-sms|title=Adventures in Unicode SMS|date=2012-11-08|publisher=Twilio|author=Chad Selph|access-date=2015-08-28|archive-url=https://web.archive.org/web/20150908104520/https://www.twilio.com/engineering/2012/11/08/adventures-in-unicode-sms|archive-date=2015-09-08|url-status=dead}}</ref><ref name="3GPP 23.038">{{cite web |url=https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=745 |title=Alphabets and language-specific information |id=3GPP TS 23.038}}</ref> 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. GSM 7-bit alphabet support is mandatory for GSM handsets and network elements.<ref name="3GPP 23.038"/>

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 part of the payload, the number of available 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,<ref>{{Cite book|last=Groves|first=Ian|url=https://www.worldcat.org/oclc/847640648|title=Mobile systems|date=1998|publisher=Springer|isbn=978-1-4615-6377-8|edition=1st|location=London|pages=70, 79, 163–66|oclc=847640648|access-date=2021-09-23|archive-date=2024-01-11|archive-url=https://web.archive.org/web/20240111044135/https://search.worldcat.org/title/847640648|url-status=live}}</ref> 10 segments is the practical maximum with some carriers,<ref>{{Cite web|url=https://help.twilio.com/articles/223181508-Does-Twilio-support-concatenated-SMS-messages-or-messages-over-160-characters|title=Does Twilio support concatenated SMS messages or messages over 160 characters?|website=Twilio Help Center|language=en-US|access-date=28 September 2024|quote=when sending very long SMS messages (longer than 10 segments with Unicode characters) some mobile carriers may have trouble handling these messages.}}</ref> and long messages are often billed as equivalent to multiple SMS messages. In some cases 127 segments are supported.<ref>{{Cite web|title=Simplifying Unicode punctuation for SMS|url=https://ssb22.user.srcf.net/adjuster/sms.html|access-date=July 15, 2021|website=ssb22.user.srcf.net|archive-date=July 15, 2021|archive-url=https://web.archive.org/web/20210715062556/https://ssb22.user.srcf.net/adjuster/sms.html|url-status=live}}</ref>

=== Interconnectivity with other networks ===
On some carriers non-subscribers can send messages to a subscriber's phone using an [[SMS gateway|Email-to-SMS gateway]]. Additionally, many carriers, including [[AT&T Mobility]], [[T-Mobile USA]],<ref>{{cite web |url=http://www.t-mobile.com/shop/addons/services/TzonesDetail.aspx?tp=Svc_Tab_TZones&tsp=Svc_Sub_Messaging&tssp=Svc_Sub_TextMessaging&oscid=4CD51BA7-B5AF-4AB2-85E0-50EC0AF141F9 |title=t-zones text messaging: send and receive messages with mobile text messaging |publisher=T-mobile.com |access-date=September 18, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20080917095859/http://www.t-mobile.com/shop/addons/services/TzonesDetail.aspx?tp=Svc_Tab_TZones&tsp=Svc_Sub_Messaging&tssp=Svc_Sub_TextMessaging&oscid=4CD51BA7-B5AF-4AB2-85E0-50EC0AF141F9 |archive-date=September 17, 2008 }}</ref> [[Sprint Nextel|Sprint]],<ref>{{cite web |url=http://support.sprintpcs.com/doc/sp7648.xml?selectedDeviceId=5707&related=y&Referring%20Related%20DocID%20List%20Index=5&docid=7434&navtypeid=10&pagetypeid=7&prevPageIndex=10 |title=Support – How do I compose and send a text message to a Sprint or Nextel customer from email? |publisher=Support.sprintpcs.com |access-date=September 18, 2008 |archive-url=https://web.archive.org/web/20081020092825/http://support.sprintpcs.com/doc/sp7648.xml?selectedDeviceId=5707&related=y&Referring%20Related%20DocID%20List%20Index=5&docid=7434&navtypeid=10&pagetypeid=7&prevPageIndex=10 |archive-date=October 20, 2008 |url-status=dead}}</ref> and [[Verizon Wireless]],<ref>{{cite web |url=http://support.vzw.com/faqs/Picture%20Messaging/faq_pixmessaging.html#item3 |title=Answers to FAQs – Verizon Wireless Support |publisher=Support.vzw.com |access-date=September 18, 2008 |archive-date=September 9, 2008 |archive-url=https://web.archive.org/web/20080909053230/http://support.vzw.com/faqs/Picture%20Messaging/faq_pixmessaging.html#item3 |url-status=dead }}</ref> offer the ability to do this through their respective websites.<ref>{{Cite journal |last=Alguliev |first=Rasim Magamed ogly |last2=Nazirova |first2=S. A. |date=2008 |title=Multilayer and Multiagent Automated Email Filtration System |url=https://doi.org/10.1615/telecomradeng.v67.i12.60 |journal=Telecommunications and Radio Engineering |volume=67 |issue=12 |pages=1089–1095 |doi=10.1615/telecomradeng.v67.i12.60 |issn=0040-2508}}</ref>

For example, an AT&T subscriber whose phone number was 555-555-5555 would receive emails addressed to 5555555555@txt.att.net as text messages. Subscribers can easily reply to these SMS messages, and the SMS reply is sent back to the original email address. Sending email to SMS is free for the sender, but the recipient is subject to the standard delivery charges. Only the first 160 characters of an email message can be delivered to a phone, and only 160 characters can be sent from a phone.  However, longer messages may be broken up into multiple texts, depending upon the telephone service provider.<ref>{{Cite web |title=Is there a maximum SMS message length? |url=http://www.textanywhere.net/faq/is-there-a-maximum-sms-message-length |publisher=TextAnywhere |access-date=May 8, 2017 |archive-date=May 8, 2017 |archive-url=https://web.archive.org/web/20170508152305/http://www.textanywhere.net/faq/is-there-a-maximum-sms-message-length |url-status=live }}</ref><ref>{{Cite web |first1=Simon |last1=Hill |first2=Andre |last2=Revilla |date=28 April 2022 |title=How to send a text message from your email account |url=https://www.digitaltrends.com/mobile/how-to-send-a-text-from-your-email-account/ |publisher=Digital Trends |quote=Keep in mind that if you’re trying to send a message that’s more than 160 characters long, it will often be sent through the Multimedia Message Service (MMS). |access-date=3 December 2022 |archive-date=3 December 2022 |archive-url=https://web.archive.org/web/20221203221043/https://www.digitaltrends.com/mobile/how-to-send-a-text-from-your-email-account/ |url-status=dead }}</ref>

Text-enabled fixed-line handsets are required to receive messages in text format. However, messages can be delivered to non enabled phones using [[Speech synthesis|text-to-speech conversion]].<ref name="Voice SMS">{{Cite news |first=John |last=Leyden |date=January 2004 |title=BT trials mobile SMS to voice landline |url=https://www.theregister.co.uk/2004/01/08/bt_trials_mobile_sms |work=[[The Register]] |access-date=May 8, 2017 |archive-date=June 29, 2017 |archive-url=https://web.archive.org/web/20170629212915/http://www.theregister.co.uk/2004/01/08/bt_trials_mobile_sms |url-status=live }}</ref>

Short messages can send binary content such as [[ringtone]]s 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 message|Smart Messaging]] is common.

GPRS is offered by smaller telco players as a route of sending SMS text to reduce the cost of SMS texting internationally.<ref name="GPRS SMS">{{Cite web |author=Ewan |date=September 1, 2006 |title=10pText.co.uk help you text internationally for 10p/text |url=http://www.smstextnews.com/2006/09/10ptextcouk_hel.html |archive-url=https://web.archive.org/web/20160304034156/http://www.smstextnews.com/2006/09/10ptextcouk_hel.html |archive-date=March 4, 2016 |publisher=SMStextnews |access-date=May 8, 2017}}</ref>

=== 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 extensions were standardised as part of the GSM Standards and extended as part of the 3GPP standards process.<ref>{{cite web|title=Use of Data Terminal Equipment – Data Circuit terminating Equipment (DTE – DCE) interface for Short Message Service (SMS) and Cell Broadcast Service (CBS)|url=https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1514|access-date=July 1, 2019|archive-date=February 16, 2020|archive-url=https://web.archive.org/web/20200216153418/https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=1514|url-status=live}}</ref>

The connection between the terminal equipment and the transceiver can be realized with a serial cable (e.g., [[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).<ref name="SMS AT extensions">{{cite web|url=http://www.developershome.com/sms/atCommandsIntro.asp|title=SMS Tutorial: Introduction to AT Commands, Basic Commands and Extended Commands|access-date=June 14, 2015|archive-date=May 9, 2008|archive-url=https://web.archive.org/web/20080509072532/http://www.developershome.com/sms/atCommandsIntro.asp|url-status=live}}</ref>

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.<ref>{{Cite web |last=Agarwal |first=Tarun |date=2019-09-18 |title=What are AT Commands : Different Types, and Their List |url=https://www.elprocus.com/at-commands-tutorial/ |access-date=2022-07-11 |website=ElProCus – Electronic Projects for Engineering Students |language=en-US |archive-date=2022-05-16 |archive-url=https://web.archive.org/web/20220516113156/https://www.elprocus.com/at-commands-tutorial/ |url-status=live }}</ref>

=== Premium-rated short messages ===
An alternative to inbound SMS is based on [[long numbers]] (international number format, such as "+44 762 480 5000"), 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 work internationally, allow businesses to use their own numbers, rather than short codes, which are usually shared across many brands. Additionally, long numbers are nonpremium inbound numbers.<ref name=":0" />

=== Threaded SMS ===
Threaded SMS is a visual styling orientation of SMS message history that arranges messages to and from a contact in chronological order on a single screen. It was first invented by a developer working to implement the SMS client for the BlackBerry, who was looking to make use of the blank screen left below the message on a device with a larger screen capable of displaying far more than the usual 160 characters, and was inspired by threaded Reply conversations in email.<ref>{{US patent|7028263}}</ref>

Visually, this style of representation provides a back-and-forth chat-like history for each individual contact.<ref>{{cite web |url=https://www.phonescoop.com/glossary/term.php?gid=455 |title=Threaded Messaging |website=Phone Scoop |access-date=29 September 2024}}</ref>  Hierarchical-threading at the [[Conversation threading#Advantages|conversation-level]] (as typical in blogs and online messaging boards) is not widely supported by SMS messaging clients.  This limitation is due to the fact that there is no [[session identifier]] or subject-line passed back and forth between sent and received messages in the [[Header (computing)|header]] data (as specified by SMS protocol) from which the client device can properly thread an incoming message to a specific dialogue, or even to a specific message within a dialogue.

=== Application-to-person (A2P) SMS ===
While SMS reached its popularity as a person-to-person messaging, another type of SMS is growing fast: application-to-person (A2P) messaging. A2P is a type of SMS sent from a subscriber to an application or sent from an application to a subscriber. It is commonly used by businesses, such as banks, e-gaming, logistic companies, e-commerce, to send SMS messages from their systems to their customers.<ref>{{Cite web|url=https://www.infobip.com/en/glossary/a2p-application-to-person-sms-messaging|title=What is A2P (Application-to-person) SMS Messaging? {{!}} Glossary|website=www.infobip.com|access-date=April 13, 2019|archive-date=January 25, 2017|archive-url=https://web.archive.org/web/20170125115455/http://www.infobip.com/en/glossary/a2p-application-to-person-sms-messaging|url-status=live}}</ref>

In the US, carriers have traditionally preferred that A2P messages be sent using a short code rather than a standard [[long code]].<ref>{{cite web|url=https://www.sinch.com/learn/what-is-a-short-code/|title=What is a Short Code?|access-date=September 23, 2015|archive-date=March 7, 2016|archive-url=https://web.archive.org/web/20160307140121/https://www.sinch.com/learn/what-is-a-short-code/|url-status=deviated}}</ref> In 2021, US carriers introduced a new service called A2P 10DLC, supporting the used of 10-digit long codes for A2P messages.<ref>{{cite web|url=https://smartercontact.com/what-is-10dlc/|title=What is A2P 10DLC and How It Impacts Your Business|date=29 December 2021 }}</ref><ref>{{cite web|url=https://www.twilio.com/en-us/blog/what-you-should-know-about-verizons-a2p-10dlc-service|title=What you should know about Verizon's A2P 10DLC Service|website=Twilio}}</ref><ref>{{cite web |title=10DLC Registration: SMS Campaign Approval and Compliance Guide |url=https://www.sent.dm/resources/10dlc-sms-registration |access-date=2024-10-27 |website=Sent.dm}}</ref> In the United Kingdom A2P messages can be sent with a dynamic 11 character sender ID; however, short codes are used for OPTOUT commands.

=== Satellite phone networks ===
While early [[Iridium Satellite LLC|Iridium]] handsets only support incoming SMS, later models can also send messages. The price per message varies for different networks. 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 web-based or email-based SMS portals where one can send free SMS to phones on that particular network.

=== Unreliability ===
Unlike dedicated texting systems like the [[Simple Network Paging Protocol]] and Motorola's ReFLEX protocol,<ref>{{cite web|url=http://findarticles.com/p/articles/mi_m0EIN/is_2000_Dec_20/ai_68271859/ |title=Motorola's ReFLEX Protocol Delivers Wireless Data With Unparelleled Nationwide Network Coverage |date=July 17, 2012|archive-url=https://archive.today/20120717132058/http://findarticles.com/p/articles/mi_m0EIN/is_2000_Dec_20/ai_68271859/ |url-status=dead|archive-date=July 17, 2012}}</ref> SMS message delivery is not guaranteed, and many implementations provide no mechanism through which a sender can determine whether an SMS message has been delivered in a timely manner.<ref name="cellular-news">{{cite web|url=http://www.cellular-news.com/story/33684.php|title=Report Says That SMS is Not Ideal for Emergency Communications|work=cellular-news|access-date=June 14, 2015|archive-date=January 25, 2015|archive-url=https://web.archive.org/web/20150125055849/http://www.cellular-news.com/story/33684.php?|url-status=live}}</ref> SMS messages are generally treated as lower-priority traffic than voice, and various studies have shown that around 1% to 5% of messages are lost entirely, even during normal operation conditions, and others may not be delivered until long after their relevance has passed.<ref>{{cite web |url=https://www.ictworks.org/sms-testing-text-message-delivery-time-and-reliability-tanzania/ |title=SMS Testing: Text Message Delivery Time and Reliability in Tanzania |date=31 August 2011}}</ref> The use of SMS as an emergency notification service in particular has been questioned.<ref name="cellular-news"/>