SIST ETS 300 625 E2:2003

SIST ETS 300 625 E2:2003 is the Slovenian identical text of ETS 300 625 Edition 2 from ETSI. It specifies the stage 1 description of Unstructured Supplementary Service Data (USSD) for GSM Phase 2, so it explains how USSD is handled between the Mobile Station (MS) and GSM Public Land Mobile Networks (PLMNs).

What does SIST ETS 300 625 E2:2003 specify?

SIST ETS 300 625 E2:2003 defines the user-level behavior of USSD in one or more GSM PLMNs. The document focuses on how a USSD string is entered, routed, responded to, and terminated, so implementers can match network behavior and handset behavior.

The document is organized into a short front matter, scope, normative references, abbreviations, and a main clause on unstructured SS data operations. Annex A is informative and gives the change history.

What are the key requirements of SIST ETS 300 625 E2:2003?

SIST ETS 300 625 E2:2003 gives the rules for mobile initiated and network initiated USSD, plus the routing and coding rules that make roaming behavior predictable. In practice, this tells the MS, the serving network, and the home network how to treat each message format.

Mobile initiated USSD

When the user enters an MMI string that GSM 02.30 treats as USSD, the MS sends it using the GSM 04.80 operation. The mobile initiated operation carries an alphabet indicator and a language indicator, with the alphabet set to SMS default alphabet and the language set to language unspecified. This matters because the handset must format the request consistently before the network can process it.

The MS may start USSD during a call or while idle. The network then checks the alphabet indicator first. If the serving network does not recognize the alphabet, it forwards the operation to the HLR; if it does recognize it, it examines the string format and applies the routing rules for the four message cases in clause 4.1.2.

Message routing and reserved formats

SIST ETS 300 625 E2:2003 reserves certain message patterns for HPLMN use and others for VPLMN use. For the reserved HPLMN cases, a visited network must pass the message directly to the HPLMN when the sender is roaming; for VPLMN-reserved cases, the VPLMN decides how to treat them. This is important for service codes and operator-specific services, especially in roaming.

For all other formats, the visited network processes the message if it can, otherwise it passes the message to the HLR. If the HLR does not support the alphabet, it informs the MS. The network ends the mobile initiated operation with either an error signal or a text response, and the response uses the GSM 03.38 default alphabet.

Cross phase compatibility

If a non-supporting network rejects a mobile initiated USSD operation, the MS retries only when the content can be encoded in IA5. This retry is made without alphabet and language indicators. The procedure is not used for failures caused by unsupported alphabet, unsupported service, or network failure, so terminals should only retry when the text itself can be represented safely.

Service code allocation

The standard says service codes for supplementary services are internationally standardized and may be used in GSM only when authorized. Only the codes specified in GSM 02.30 and the codes defined in the reserved cases may be used. For operators, this is the control point that prevents clashes between national, operator-specific, and standardized service codes.

Network initiated USSD

A network may send an unstructured string to the MS while it is registered. The network initiated operation also carries alphabet and language indicators, chosen by the operator. If the MS cannot process it, or cannot support the indicated alphabet, it returns an error to the originating node.

If the network requires a user response, the next MMI string entered by the user becomes the response, and the MS must provide a way to end the dialogue with a null response. If no response is requested, normal MMI behavior continues. This is the basis for interactive USSD services such as menu-based network dialogues.

What terms does SIST ETS 300 625 E2:2003 define?

Unstructured Supplementary Service Data (USSD) is a GSM supplementary service for sending unstructured strings between the MS and the network.

Mobile Station (MS) is the user equipment that sends and receives USSD and handles the MMI.

Public Land Mobile Network (PLMN) is the GSM network environment for which USSD behavior is defined.

Home PLMN (HPLMN) is the subscriber’s home network, which receives certain reserved USSD formats directly.

Visited PLMN (VPLMN) is the roaming network that may handle its own reserved USSD formats.

Home Location Register (HLR) is the network node that may receive forwarded USSD when the serving network cannot process it.

Man-Machine Interface (MMI) is the command interface on the MS that the user uses to enter USSD strings.

Who uses SIST ETS 300 625 E2:2003?

SIST ETS 300 625 E2:2003 is used by GSM network operators, roaming and interconnect engineers, MS vendors, and service designers who implement USSD-based services. Quality and interoperability teams use it to verify that handset behavior, network routing, and service code handling match the GSM USSD rules. Buyers and integrators use it when they need equipment that supports USSD dialogs in GSM PLMNs.

What changed in SIST ETS 300 625 E2:2003 from the previous edition?

SIST ETS 300 625 E2:2003 is the second edition. The change history records a clarification of USSD transmission in clauses 4.1.2 and 4.2.2.

Which standards are used with SIST ETS 300 625 E2:2003?

• GSM 01.04 (ETR 100) - provides abbreviations and acronyms used in the standard.
• GSM 02.04 (ETS 300 503) - gives the general rules for supplementary services.
• GSM 02.30 (ETS 300 511) - defines the MMI of the MS and the string formats that trigger USSD handling.
• GSM 03.38 (ETS 300 537) - defines the alphabets, including the default alphabet used for responses.
• GSM 04.80 (ETS 300 564) - defines the layer 3 supplementary service formats and coding used to carry USSD operations.

What does the SIST ETS 300 625 E2:2003 document contain?

The document is a procedural specification of USSD behavior rather than a test method. Clause 4 describes mobile initiated and network initiated operations, including alphabet indicators, language indicators, routing decisions, response handling, and dialogue termination. It also covers cross phase compatibility and the allocation of service codes for supplementary services. Annex A gives the recorded change history, which is useful when tracking edition differences during implementation or audit work.