22.1123GPPRelease 8Stage 1TSUSIM Application Toolkit (USAT) Interpreter
5.1 Application system
This entity is a collection of systems that utilise the USAT interpreter for services requiring the usage of USIM specific services, e.g., security. A special case is the provision of dynamic content for delivery via USAT, e.g. web server or an application.
The application system may contain symmetric or asymmetric keys for secure end-to-end application delivery.
The application system shall provide an HTTP interface to the USAT Gateway.
5.2 USAT Gateway
The USAT Gateway converts between the "Application to USAT Gateway Protocol" and the "USAT Gateway to USAT Interpreter Protocol".
The USAT Gateway may contain keys for secure transport delivery using TS 23.048 . This system shall provide interfaces to the application systems and to the access nodes.
5.2.1 Blocking mechanisms
The USAT Gateway shall be able to reject application containing forbidden functionality. Forbidden functionality is a set of functionality restricted on a application system basis or on an USIM basis. E.g., a restriction of functionality available could be made based on the level of trust of the application system or on the subscription type of the user.
The blocking mechanism generates an error as defined by the USAT Gateway error handling.
5.2.2 Error handling
When the USAT Gateway rejects user requested content, the subscriber shall be informed by the USAT Gateway.
Samples for possible error reasons are:
– not supported mark-up language tags;
– not supported attributes;
– bad message structure;
– security requirements not fulfilled;
– internal errors;
– rejection by busy USAT Interpreter;
– communication failure;
5.3 Access Node
This entity provides the transparent transport of the USAT Gateway to USAT Interpreter content. This can be SMS or GPRS or any other service available now or in the future, which is able to provide a transparent data channel to the USIM with USAT Interpreter.
5.4 Mobile Equipment
The mobile equipment provides the transparent transport of the USAT Gateway to USAT Interpreter content. For GPRS the ME decodes the IP-packets.
5.5 USIM with USAT Interpreter and stored applications
This entity converts USAT Gateway to USAT Interpreter protocol to local USIM commands. The local USIM commands could be USAT commands or other commands necessary, e.g., security commands, to execute the application. The USAT Interpreter shall use the commands defined in TS 31.111  to communicate with the ME. The USIM with USAT Interpreter may contain keys for both secure end-to-end application delivery and secure transport.
It shall provide memory space for locally stored translated applications.
The USAT Interpreter shall be configurable to allow or deny the execution of specific low level commands.
The USAT Interpreter can be triggered either
– locally from the ME, as a result from a menu selection,
– locally from the ME, as a result from an event,
– by an incoming page as a result from a previous URL request from the USAT Interpreter, or
– by an incoming page initiated by an application system (push).
A caching mechanism may be used by the USAT Interpreter.
The USAT Interpreter shall provide a generic interface to support all USAT commands.
The following table describes the list of additional functionality to be provided by the USAT Interpreter:
Table 1: Additional USAT Interpreter functionality
Support mark-up language mediation
Go (branching to a URL)
Variables (referencing, substituting,…)
Support of different variable types, including type checking and type conversion
Supported types of variables
Soft-Key support (e.g. Do tags)
Minimum Navigation Units: Cards and Decks (or similar for non-WML mark-up languages)
– Go homepage (specific URL)
– Go Back
This function is depending of the current context and can result in:
– Restart current Navigation Unit
– Step back previous Navigation Units
– Go back (history functionality of visited URLs during the current USIM session)
Unconditional branching (forward and backward)
Concatenation of strings
Environment variables (USIM/USAT/USAT Interpreter platform information available to all services)
Variable value sharing between decks/pages (or similar for non-WML mark-up languages) within a session
Permanent variable value sharing between sessions and applications
Execution of locally stored translated content
Ciphering / Authentication
End-to-End security based on symmetric algorithms
End-to-End security based on asymmetric algorithm schemes
Execution of an external function
Bookmark storage of the current page on
– USAT Gateway or
– locally at USAT Interpreter by the end user
Support for caching