Unstructured Supplementary Service Data Unstructured Supplementary Service Data (USSD), sometimes referred to as "quick codes" or "feature codes", is a communications protocol used by GSM cellular telephones to communicate with the mobile network operator's computers. USSD can be use ...

, or USSD is a

communication protocol A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchroniza ...

used by GSM cellular telephones to communicate with the service provider's computers. A gateway is the collection of hardware and software required to interconnect two or more disparate networks, including performing protocol conversion.Webster's New World Telecom Dictionary Copyright © 2010 by Wiley Publishing, Inc., Indianapolis, Indiana. http://computer.YourDictionary.com/gateway

Functionality

A USSD gateway routes USSD messages from the signalling network to a service application and back. A 'USSD gateway' service is also called a 'USSD center'. USSD gateway is based upon the ability of the delivery agent or the source to send and receive USSD messages. A USSD is a session-based protocol. USSD messages travel over GSM signalling channels, and are used to query information and trigger services. Unlike similar services (

SMS Short Message/Messaging Service, commonly abbreviated as SMS, is a text messaging service component of most telephone, Internet and mobile device systems. It uses standardized communication protocols that let mobile devices exchange short text ...

and MMS), which are

store and forward Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in ...

based, USSD establishes a real time session between mobile handset and application handling the service.

Difference between USSD and other gateways

The difference between USSD gateways and other messaging gateways is that USSD gateways maintain a single interactive session once the connection is established.

and MMS store and forward messages independently of the user session, similar to the way

email Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic ( digital) version of, or counterpart to, mail, at a time when "mail" mean ...

is sent over the

internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a ''internetworking, network of networks'' that consists ...

Modular operation

#Session module: as per directions from the Signalling System No. 7 (SS7) protocol stack's

Mobile Application Part The Mobile Application Part (MAP) is an SS7 protocol that provides an application layer for the various nodes in GSM and UMTS mobile core networks and GPRS core networks to communicate with each other in order to provide services to users. Th ...

(MAP), it receives and sends out session IDs from the session ID pool, and maintains and destroys the sessions. #MAP layer:

is present both on the server and on the MS. #Gateway: a gateway will wait for messages from the MAP layer, and work to route these messages into

Short Message Peer-to-Peer Short Message Peer-to-Peer (SMPP) in the telecommunications industry is an open, industry standard protocol designed to provide a flexible data communication interface for the transfer of short message data between External Short Messaging Entit ...

(SMPP) protocol, which is then delivered to the server applications. This is the most important operation, and this is the reason why USSDs are primarily used, as it helps to directly connect users to applications like bill checking and others. #Locator: this tries to find out the current

cell site A cell site, cell tower, or cellular base station is a cellular-enabled mobile device site where antennas and electronic communications equipment are placed (typically on a radio mast, tower, or other raised structure) to create a cell, or adj ...

, and relays it to the gateway. Then the messages are routed using Routing Numbers. #

Home Location Register Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mo ...

: this is the home zone where the given cell phone's number is registered in the database. This is different from the

Visitor Location Register Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call out and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mo ...

which is where the user is roaming. #The reason why USSD is commonly used is because it enhances the

WCDMA The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. Developed and maintained by the 3GPP (3rd Generation Partnership Project), UMTS is a component of the I ...

signalling and multiplexes the coherent signals. ;Types of applications *Balance Check: the user can send a Process Supplementary Service request (PSSR) to the home zone, which will forward this, under guidance from the gateway, to the correct application. Then, the application sends an acknowledgement via USSD gateway, HLR etc., known as PSSR response back to the user. Balance Notification at the end of charged call can also be given using Unstructured Supplementary Service Notify (USSN) message. *Voice Chat: using the same process as above, one can use voice chat. This is highly useful when

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Interne ...

enabled phones are not available. *Advertising: the application can advertise their product using USSD, which is less invasive than

telemarketing Telemarketing (sometimes known as inside sales, or telesales in the UK and Ireland) is a method of direct marketing in which a salesperson solicits prospective customers to buy products or services, either over the phone or through a subseque ...

. *Roaming: this has huge advantages while roaming. This is because USSD services are well available in roaming networks, and all the USSD messages are directed towards the subscriber's Home Network itself, thus, same set of services that are available in home network can be given in visited network too, giving subscribers a Virtual Home Environment (VHE). Apart from PSSR and USSN, there is another method called Unstructured Supplementary Service Request (USSR) message that initiates a session by USSD Gateway to a Mobile User. This message can be used in conjunction with USSR initiated session to provide session based services like Menu services through USSD. Also, in the earlier phases of MAP (

), PSSR message was called PSSD (PSS Data).

Functionality

Difference between USSD and other gateways

Modular operation

References

Further reading