Editing Unstructured Supplementary Service Data

{{Short description|Communications protocol}}
{{Redirect|USSD|the organization|United States Society on Dams}}
[[Image:USSD soneric.jpg|thumb|150px|USSD on a [[Sony Ericsson]] mobile phone (2005)]]
{{Anchor|USSD for the layman}}
'''Unstructured Supplementary Service Data''' ('''USSD'''), sometimes referred to as "'''quick codes'''" or "'''feature codes'''", is a [[communications protocol]] used by [[GSM]] [[cellular telephone]]s to communicate with the [[mobile network operator]]'s computers. USSD can be used for [[Wireless Application Protocol|WAP]] browsing, prepaid callback service, mobile-money services, location-based content services, menu-based information services, and as part of configuring the phone on the network.<ref name="telecomspace">{{cite web|title=Unstructured Supplementary Services Data (USSD)|work=Telecom Space|access-date=August 23, 2010|url=http://www.telecomspace.com/messaging-ussd.html|archive-date=March 3, 2021|archive-url=https://web.archive.org/web/20210303081521/http://www.telecomspace.com/messaging-ussd.html|url-status=dead}}</ref> The service does not require a messaging app, and does not incur charges.<ref name=scard>{{cite web | last=Scard | first=Jen | title=What is USSD? | website=Wireless Logic| date=12 July 2022 | url=https://www.wirelesslogic.com/iot-glossary/what-is-ussd/}}</ref>

USSD messages are up to 182 alphanumeric characters long. Unlike [[SMS|short message service (SMS)]] messages, USSD messages create a real-time connection during a USSD session. The connection remains open, allowing a two-way exchange of a sequence of data. This makes USSD faster than services that use SMS.<ref name="telecomspace"/>

While [[GSM]] is being phased out in the 2020s with [[2G]] and [[3G]] technologies, USSD services can be supported over [[LTE (telecommunication)|LTE]] and [[5G]].

== Uses ==
When a user sends a message to the phone company network, it is received by a computer dedicated to USSD. The computer's response is sent back to the phone, generally in a basic format that can easily be seen on the phone display. Messages sent over USSD are not defined by any [[standardization]] body, so each network operator can implement whatever is most suitable for its customers.

[[Image:USSD MaxisHotlink.png|thumb|150px|USSD on a [[Google Pixel]] device (2018). The user submits a code corresponding to the service available]]

USSD can be used to provide independent calling services such as a [[Callback (telecommunications)|callback]] service (to reduce phone charges while roaming), enhance mobile marketing capabilities or interactive data services.

USSD is commonly used by prepaid GSM cellular phones to query the available balance. The vendor's "check balance" application hides the details of the USSD protocol from the user. On some [[Prepaid mobile phone|pay as you go]] networks, such as [[Tesco Mobile]], once a user performs an action that costs money, the user sees a USSD message with their new balance. USSD can also be used to refill the balance on the user's [[SIM card]] and to deliver [[one-time password]]s or PIN codes.

Some operators use USSD to provide access to real-time updates from social-networking websites including [[Facebook]] and [[Twitter]].<ref>{{cite web |url=https://www.datareign.com/tata-docomo-starts-ussd-services-to-facebook-and-twitter.html |title=TATA Docomo introduces Facebook, Twitter access via USSD |date= 16 July 2011 |access-date= 12 Nov 2019}}</ref> Between 2012 and 2018, the [[Wikipedia Zero]] project provided access to Wikipedia articles via USSD.<ref>{{cite web|url=http://blog.wikimedia.org/2013/02/22/getting-wikipedia-to-the-people-who-need-it-most/|last=Wadhwa|first=Kul|title=Getting Wikipedia to the people who need it most|date=22 February 2013|work=Wikimedia blog|publisher=Wikimedia Foundation}} (Page now obsolete and invalid.)</ref>

USSD is sometimes used in conjunction with SMS. The user sends a request to the network via USSD, and the network replies with an acknowledgement of receipt:
:"Thank you, your message is being processed. A message will be sent to your phone."

Subsequently, one or more mobile terminated SMS messages communicate the status and/or results of the initial request.<ref>{{cite web |title=Monitor usage on your phone |access-date=14 May 2012 |work=AT&T Residential Wireless Support |url=http://www.att.com/esupport/article.jsp?cv=820&sid=KB64693 |archive-url=https://web.archive.org/web/20120511153629/https://www.att.com/esupport/article.jsp?cv=820&sid=KB64693 |archive-date=11 May 2012 |url-status=dead }}</ref> In such cases, SMS is used to "push" a reply or updates to the handset when the network is ready to send them.<ref>{{cite web|title=Manage your account|url=http://www.att.com/esupport/article.jsp?sid=53414|work=AT&T Residential Wireless Support|publisher=AT&T|access-date=11 May 2013}}</ref> In contrast, USSD is used for command-and-control only.

== Technical details {{Anchor|USSD for the GSMA aficionados}} ==
Most GSM phones have USSD capability.<ref>{{cite web|title=Windows Phone 7 doesn't support USSD|url=http://answers.microsoft.com/en-us/winphone/forum/wp7-wpstart/ussd-service/80ce77d9-5b46-4bbc-9a8f-c209f566f9a9|archive-url=https://web.archive.org/web/20120703033325/http://answers.microsoft.com/en-us/winphone/forum/wp7-wpstart/ussd-service/80ce77d9-5b46-4bbc-9a8f-c209f566f9a9|archive-date=3 July 2012|website=Microsoft Answers|date=8 February 2012}}</ref> USSD is generally associated with real-time or instant messaging services. An [[Short message service center|SMSC]] is not present in the processing path, so that the [[store-and-forward]] capability supported by other short-message protocols such as SMS is not available.

USSD Phase 1, as specified in GSM 02.90, only supports mobile-initiated ("pull") operations.<ref>{{cite web|title=GSM 02.90 (ETSI TS 100 625, V7.0.0) Specification (USSD) – Stage 1|url=http://www.3gpp.org/ftp/Specs/html-info/0290.htm|work=3gpp.org|publisher=3rd Generation Partnership Project|access-date=11 May 2013}}</ref> In the [[Network switching subsystem|core network]], the message is delivered over [[Mobile Application Part|MAP]], USSD Phase 2, as specified in GSM 03.90.<ref>{{cite web|title=GSM 03.90 (ETSI TS 100 549, V7.0.0) Specification (USSD) – Stage 2|url=http://www.3gpp.org/ftp/Specs/html-info/0390.htm|work=3gpp.org|publisher=3rd Generation Partnership Project|access-date=11 May 2013}}</ref> After entering a USSD code on a [[GSM]] handset, the reply from the [[GSM]] operator is displayed within a few seconds.

While GSM is being phased out in the 2020s with [[2G]] and [[3G]],  a solution is available for supporting USSD services directly from the [[LTE (telecommunication)|LTE]]/[[5G]]/[[IP Multimedia Subsystem|IMS]] network, providing a similar user experience as in GSM.<ref name=kulkarni>{{cite web | last=Kulkarni | first=Ajay | title=The Future of USSD in the Telecommunications space | website=Comviva | date=10 December 2020 | url=https://www.comviva.com/blog/mobile-data-platform/the-future-of-ussd-in-the-telecommunications-space/}}</ref>

===Format===
A USSD message typically starts with an asterisk symbol (*) or a hash symbol (#) and is terminated with a hash symbol (#).  A typical message comprises digits for commands or data; groups of digits may be separated by additional asterisks.<ref name="telecomspace"/>

USSD mode

Mobile-initiated
* USSD/ PULL or USSD/ P2A
* when the user dials a code, e.g. *139# from a GSM mobile handset

Network-initiated
* USSD/ PUSH or USSD/A2P
* when the user receives a push message from the network; primarily used for promotional services
{| class="wikitable"
! Example USSD codes
|-
| *101#
|-
| *139*1*1234567890#
|}

==Man-Machine Interface==
'''The codes below are not USSD codes''', these are the related Man-Machine Interface (MMI); they are standardized so they are the same on every GSM phone. They are interpreted by the handset first before a corresponding command (not the code itself) is sent to the network. These codes might not always work when using an AT interface; there are standard AT commands defined for each of these actions instead.<ref>{{cite web |url= http://www.etsi.org/deliver/etsi_ts/122000_122099/122030/10.00.00_60/ts_122030v100000p.pdf |format= pdf |title= Man-Machine Interface (MMI) of the User Equipment - ETSI TS 122 030 V10.0.0 |date= May 2011 |pages= 30 }}</ref><ref>{{Cite web|url=http://berlin.ccc.de/~tobias/mmi-ussd-ss-codes-explained.html|title = What's the difference between USSD, MMI and SS codes?}}</ref>

'''BS''' is the type of bearer service, some valid values are:

'''11''' for voice

'''13''' for fax

'''16''' for SMS (only valid for barring)

'''25''' for data

=== <leave blank> for all. ===

=== T is number of seconds for the No Reply Condition Timer, default is 20 seconds if not specified. ===
{| Class = "wikitable sortable"
|+ GSM USSD codes and their functions with various network operators
! Code !! Function !! Note !! Switch on !! Switch off !! Display status
|-
| 002
| all diversions
| unconditional, busy, unreachable, does not answer
| * * 002 * '''number''' * '''BS''' * '''T''' #
| # # 002 * * '''BS''' #
| * # 002 * * '''BS''' #
|-
| 004
| all conditional redirections
| busy, unreachable, does not answer
| * * 004 * '''number''' * '''BS''' * '''T''' #
| # # 004 * * '''BS''' #
| * # 004 * * '''BS''' #
|-
| 03
| Change Network password
| password is network dependent, default on some networks is 0000. See call barring functions *33
| colspan = "3"| * * 03 * 330 * '''old password''' * '''new password''' * '''new password''' #
|-
| 04
| Change [[Personal identification number|PIN]]
|
| colspan = "3"| * * 04 * '''old PIN''' * '''new PIN''' * '''new PIN''' #
|-
| 042
| Change PIN2
| Only with Phase 2 SIM
| colspan = "3"| * * 042 * '''old PIN2''' * '''new PIN2''' * '''new PIN2''' #
|-
| 05
| Change PIN by [[Personal unblocking code|PUK]]
|
| colspan="3"| * * 05 * '''PUK''' * '''new PIN''' * '''new PIN''' #
|-
| 052
| Change PIN2 via PUK
| Only with Phase 2 SIM
| colspan = "3"| * * 052 * '''PUK''' * '''new PIN2''' * '''new PIN2''' #
|-
| 06
| read device number ([[International Mobile Station Equipment Identity|IMEI]])
|
| colspan = "3"| * # 06 #
|-
| 21
| unconditional divert
| all incoming calls will be diverted
| * * 21 * '''number''' * '''BS''' #
| # # 21 * * '''BS''' #
| * # 21 * * '''BS''' #
|-
| 30
| get the [[Caller ID|caller's number]] displayed (CLIP)
| as a callee get the CLIP displayed
| * 30 #
| # 30 #
| * # 30 #
|-
| 31
| suppressing the transmission of caller's phone number (CLIR)
| for all subsequent calls
| # 31 #
| * 31 #
| * # 31 #
|-
| 31
| temporary change of the transmission of CLIR
| valid just for the next call; no final #
| # 31 # '''number'''
| * 31 # '''number'''
|
|-
| 330
| total incoming and outgoing service barring
| password is network dependent, default on some networks is 0000
| * 330 * '''password''' * '''BS''' #
| # 330 * '''password''' * '''BS''' #
| * # 330 * * '''BS''' #
|-
| 33
| outgoing call barring
| password is network dependent, default on some networks is 0000
| * 33 * '''password''' * '''BS''' #
| # 33 * '''password''' * '''BS''' #
| * # 33 * * '''BS''' #
|-
| 331
| outgoing international call barring
| password is network dependent, default on some networks is 0000
| * 331 * '''password''' * '''BS''' #
| # 331 * '''password''' * '''BS''' #
| * # 331 * * '''BS''' #
|-
| 332
| outgoing international call barring, excluding to home
| password is network dependent, default on some networks is 0000
| * 332 * '''password''' * '''BS''' #
| # 332 * '''password''' * '''BS''' #
| * # 332 * * '''BS''' #
|-
| 333
| total outgoing service barring
| password is network dependent, default on some networks is 0000
| * 333 * '''password''' * '''BS''' #
| # 333 * '''password''' * '''BS''' #
| * # 333 * * '''BS''' #
|-
| 35
| incoming call barring
| password is network dependent, default on some networks is 0000. Incompatible with call diversion
| * 35 * '''password''' * '''BS''' #
| # 35 * '''password''' * '''BS''' #
| * # 35 * * '''BS''' #
|-
| 351
| incoming call barring, when international roaming
| password is network dependent, default on some networks is 0000
| * 351 * '''password''' * '''BS''' #
| # 351 * '''password''' * '''BS''' #
| * # 351 * * '''BS''' #
|-
| 353
| total incoming service barring
| password is network dependent, default on some networks is 0000
| * 353 * '''password''' * '''BS''' #
| # 353 * '''password''' * '''BS''' #
| * # 353 * * '''BS''' #
|-
| 37
| Call back on busy (CCBS)
| valid on some mobile networks only
| * 37 #
| # 37 #
| * # 37 #
|-
| 43
| incoming call notification when busy
| aka call waiting
| * 43 * '''BS''' #
| # 43 * '''BS''' #
| * # 43 * * '''BS''' #
|-
| 61
| call divert when not answered
|
| * * 61 * '''number''' * '''BS''' * '''T''' #
| # # 61 * * '''BS''' #
| * # 61 * * '''BS''' #
|-
| 62
| call divert when off or not reachable
|
| * * 62 * '''number''' * '''BS''' #
| # # 62 * * '''BS''' #
| * # 62 * * '''BS''' #
|-
| 67
| call divert when busy or pressing reject
|
| * * 67 * '''number''' * '''BS''' #
| # # 67 * * '''BS''' #
| * # 67 * * '''BS''' #
|-
! Code !! Function !! Note !! Switch on !! Switch off !! Display status
|}

==See also==
* [[USSD Gateway]]
* [[Ultra Mobile Broadband]]
* [[Supplementary service codes]]
* {{section link|Call forwarding|Mobile (cell) phones}}
* [[SIM Application Toolkit]]

== References ==
{{Reflist}}

==External links==
* [http://www.3gpp.org/ftp/Specs/html-info/0490.htm GSM 04.90 (ETSI EN 300 957, V7.0.1) Specification (USSD)] Stage 3 – 3GPP
* [http://www.3gpp.org/ftp/Specs/html-info/22030.htm 3GPP TS 22.030]
* [https://berlin.ccc.de/~tobias/mmi-ussd-ss-codes-explained.html What’s the difference between USSD, MMI and SS codes?]
* [https://www.dtechy.com/android-ussd-codes-list/ Android USSD codes list (MMI code list)]

[[Category:Mobile telecommunications standards]]
[[Category:3GPP standards]]
[[Category:GSM standard]]