Implementation eXtra Information for Testing Proforma

Description

The IXIT proforma is a document defined in 3GPP specifications for conformance testing, particularly for User Equipment (UE) testing. IXIT stands for Implementation eXtra Information for Testing. The proforma is a structured questionnaire that, when completed for a specific UE under test (UEUT), becomes the IXIT. The IXIT provides the test system with implementation-specific details that are not otherwise available from the UE's standard interface, such as supported features, configuration parameters, and optional capabilities. This information is essential for selecting and parameterizing test cases correctly.

In the 3GPP conformance testing framework, the IXIT proforma is referenced in specifications such as TS 36.523 (E-UTRA UE conformance specification), TS 37.571 (multi-RAT UE conformance), TS 38.508 (5G UE conformance), TS 38.522 (5G UE conformance test specifications), and TS 38.523 (5G UE conformance test specification for protocol). The proforma is typically provided by the test house or test equipment vendor and is filled out by the UE manufacturer or supplier. The completed IXIT is then used by the test system to configure the test environment and to determine which test cases are applicable.

The IXIT proforma covers a wide range of information. It may include details about the UE's supported frequency bands, radio capabilities, protocol options, security algorithms, and optional features. It may also include information about the UE's behavior in specific scenarios, such as handling of certain messages or timers. Because many 3GPP test cases are conditional on the UE's capabilities, the IXIT ensures that only relevant tests are executed and that test parameters are set correctly. This avoids false failures and reduces test time.

The proforma is structured as a questionnaire with predefined questions and answer formats. It is designed to be machine-readable or at least easily parsed, so that the test system can automatically extract the necessary information. The IXIT is not a substitute for the UE's declared capabilities over the air interface; rather, it supplements them with information that is needed for test execution but not signalled by the UE. For example, the UE may support a feature but not indicate it in a standard message, or the test may require knowledge of internal configuration that is not exposed.

In terms of evolution, the IXIT proforma was introduced in Rel-15, coinciding with the first release of 5G NR specifications. It was defined to support the testing of 5G UEs, which have a large number of optional features and configurations. The definition text remained essentially unchanged from Rel-15 through Rel-19, with only minor punctuation and formatting differences. The proforma is maintained in the relevant conformance test specifications and is updated as new features are added to the standard.

Purpose & Motivation

The IXIT proforma exists to solve a fundamental problem in conformance testing: test cases must be applicable to a wide range of UE implementations, but many test procedures depend on implementation-specific details that are not standardized or not signalled over the air interface. Without a way to capture this information, test systems would either have to run all possible test variants (which is inefficient) or make assumptions that could lead to incorrect test verdicts.

The proforma provides a standardized questionnaire that UE vendors fill out for each device model. This ensures that the test system has the necessary information to select the right test cases and configure them correctly. It also provides a consistent format for this information, making it easier for test houses to automate test execution and for vendors to provide the data.

Historically, similar concepts existed in earlier 3GPP releases for 2G and 3G testing, but the IXIT proforma as a formalized document was introduced in Rel-15 to address the complexity of 5G NR. The large number of optional features and flexible configurations in 5G made it impractical to rely on implicit knowledge or ad-hoc information exchange. The IXIT proforma therefore became a key tool for ensuring that 5G UE conformance testing is efficient, repeatable, and fair.