Efficient Programming Interface for UMTS Protocol Development

3GPP-specific commands and must be Adapting this DLL to the DUT takes rela- Summary adapted to the specific mobile phone tively little time if you consider that this being tested by means of proprietary up-front work reduces test time and that By providing test-case automation, commands. This requires a knowledge no personnel is needed during testing. Rohde & Schwarz has increased the of Visual C++. It should also be men- This means that you can use the protocol value of the R&S ® CRTU-G even further. tioned here that the Automation DLL tester virtually around the clock. A universal mechanism that requires project basically contains two modules: only a little up-front effort saves sub- the comport.c module, which contains You can monitor the commands stantial time later on. For details, refer to all functions that involve the COM port, exchanged between the R&S ® CRTU-G the R&S ® CRTU-G documentation. and the MS_Auto_RS232.cpp module, and the mobile phone by using the Gerhard Götz which contains all mobile-phone-spe- AutoDLL Traffic Viewer. This tool is also cific commands. For details, refer to the helpful when developing a Customer R&S ® CRTU-G software manual. Automation DLL.

Protocol Tester R&S ® CRTU-W Efficient programming interface for UMTS protocol development

The R&S ® CRTU-W (FIG 1) has long Intelligent compromise

been known for its convenient and The use of the R&S ® CRTU-W as a test tool in UMTS protocol development powerful TTCN interface, which was places very high demands on the programming interface. The vast number of designed and optimized for confor- parameters specified by the 3GPP standard as well as the variety of applica- mance testing. Research and develop- tions call for an intelligent compromise between flexibility and convenience. The 43793/5 ment, however, require a flexible yet R&S ® CRTU-W now comes with a new FIG 1 The Protocol Tester R&S ® CRTU-W – software option – MLAPI (Medium Level a flexible test platform for the development and easy to operate programming inter- C++ Programming Interface) – that pro- certification of WCDMA user equipment. vides the right answer. face. The new MLAPI software option to handle the constraints inherent in the (R&S ® CRTU-WT02) now provides Convenience and flexibility TTCN programming language as well as in the architecture of the 3GPP test you with the right tool for R&D The test cases specified by 3GPP for suites and the extra tools required. conformance testing of UMTS mobile applications. phones [1, 2] are already implemented in To meet this need, Rohde & Schwarz the R&S ® CRTU-W. Research and devel- has developed the MLAPI programming opment, however, require a program- interface. It enables you to create proto- ming interface that offers greater flexi- col layer 3 user-defined scenarios in the bility and convenience. It must be able C++ programming language. The meth-

17 News from Rohde & Schwarz Number 182 (2004/II) MOBILE RADIO Protocol testers

ods of handling protocol messages as Since users of the C++ programming tool which is also based on the MDDB well as the modelling of dynamic oper- interface are usually interested in the has been implemented for this purpose ation cover a wide range of applica- detailed definition and full flexibility of – the Message Composer (FIG 4). This tions, from simple to very powerful. For the RRC PDU covering all parameters tool enables you to conveniently perform example, you might want to set a mobile rather than in the complex configuration any modifications to the scenario behav- phone to a defined signalling state by of the lower layers, offering the actual iour that are coded in the protocol mes- using a simple sequence of messages RRC PDU as a “single-source” interface sages without having to recompile the and then implement a desired applica- is a good approach. scenario. tion in this state. Or, you might employ complex alternatives or deliberately As a result, the MLAPI protocol stack To allow received messages to be cause a faulty response in order to test provided by Rohde & Schwarz con- checked against predefined receive con- the signalling function. tains not only the lower protocol layers straints, they are not stored in purely but also the part of the RRC layer that hexadecimal format. Rather, they must is responsible for the configuration of support wildcards that, for example, Concept of automatic the lower layers, hence the designa- allow a defined list of values or any configuration tion “Medium Level“. Thus, when you value (ANY) to be assumed by a specific send an RRC PDU from your scenario, subelement. These values can also be Due to the quality of service (QoS) archi- the required information is automatically graphically defined with the Message tecture of the UMTS standard, higher extracted and passed on to the lower Composer and are highlighted in colour protocol layers request the transmis- layers. This considerably reduces error (FIG 4). The C++ programming interface sion quality for a specific application rate and program size without any loss also offers a simple macro that performs in abstract form, whereas the actual of flexibility. the comparison automatically. If there is parameters for channel configura- no match, the discrepancy will be indi- tion are known only in the lower layers cated in the subelement tree. (referred to as access stratum, AS). New dimensions in protocol These parameters are very numerous, message handling however, and can be combined in a vari- Intelligent organization of ety of ways. UMTS differs from GSM in The basic software for the R&S ® CRTU-W dynamic behaviour that the top AS layer, i.e. the RRC [3], is provides a library (MDDB) for handling responsible for managing these param- protocol messages. The library is auto- The MLAPI offers simple macros for eters and their combinations. The strat- matically generated from the message defining state machines to enable effi- egy for assigning these parameters is specifications and includes all methods cient programming even for complex, implemented by the network opera- of handling such messages. For example, branched operations. The reception of a tor. The parameter information is coded the Message Analyzer uses the MDDB message – or more generally speaking as RRC protocol data (PDUs) using com- to completely decode recorded proto- an event – is represented by a transition plex elements described in the ASN.1 col messages and interpret subelement within a state. If and to what extent dif- language and transmitted to the mobile values in text form. ferent states or state machines are actu- phone. The base station and the mobile ally used is up to you. phone must configure their lower proto- All MDDB methods are available for the col layers accordingly before data can be C++ pogramming interface, including Further powerful functions are avail- transmitted at the required QoS (FIG 2). read and write access to any desired able for optimizing scenario modular- Similar processes take place during hand- subelements, cloning of substruc- ity. State machines can be run in parallel over and other main procedures. tures, reading and storage of mes- or be derived from one another, making sage instances – in hexadecimal or XML it easy for you to define a common In contrast to other layer 3 messages, format – and many more. Simple macros means of handling exceptions for a spe- the RRC PDUs therefore contain infor- are available for transmitting and receiv- cific number of procedures, for example. mation not only for the peer station but ing any layer 3 PDU. Moreover, state machines can mutually also for local configuration. The configu- call each other, allowing you to design ration interfaces of the lower layers are Being able to define message instances a procedure-oriented scenario. The pro- usually proprietary, whereas the RRC is one of the programming interface‘s gramming interface further provides con- PDU is defined by the 3GPP standard [3]. main features. Therefore, a graphical venient means of defining timers, delays,

18 News from Rohde & Schwarz Number 182 (2004/II) FIG 2 QoS and UMTS �� protocol structure. �� Important abbreviations �� 3GPP 3rd Generation Partnership �� Project AMR Adaptive Multirate �� AS Access Stratum �� ASN.1 Abstract Syntax Notation One �� CS Circuit Switched �� EMMI Electrical Man-Machine Interface �� HSDPA High Speed Downlink Packet Access �� IP Internet Protocol �� MAC Medium Access Control

�� MDDB Message Description Data Base �� MLAPI Medium Level C++ Pro- gramming Interface MMS Multimedia Message Service PDCP Packet Data Convergence �� Protocol �� PDU Protocol Data Unit �� PS Packet Switched QoS Quality of Service �� RAT Radio Access Technology

�� RLC Radio Link Control RRC Radio Resource Control �� TTCN Tree and Tabular Combined �� Notation �� UMTS Universal Mobile Telecom- munications System WAP Wireless Application Protocol FIG 3 Modularization of the dynamic behaviour of a scenario.

FIG 4 Message Composer with receive constraints check.

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triggers, as well as the parameterization Summary and future ferences will soon be possible, as well for passing messages or other informa- developments as the scaling of several protocol tes- tion to additional state machines. ters for multicell and handover scenar- The MLAPI is a tool for UMTS protocol ios. Moreover, Rohde & Schwarz plans The MLAPI software option already con- development that optimally combines to expand the programming interface to tains a number of example scenarios flexibility with convenience. Due to the enable you to control a Protocol Tester in the form of compilable source code. unique interface design, test scenarios R&S ® CRTU-G using the same philosophy These scenarios show how to use all can be created with considerably less as for the R&S ® CRTU-W. This will allow essential interface elements. They also effort. The concept of automatic config- you to define 2G3 inter-RAT handover implement standard applications such uration of the lower protocol layers fur- scenarios [6]. as CS registration and PS attach, AMR ther contributes to efficiently generating speech call, PS data call, CS/PS multi- and maintaining test scenarios. Plus, you Rohde & Schwarz increasingly offers call, soft and hard handover. Being of can easily integrate your own protocol packages of ready-to-run scenarios that modular design (FIG 3), the scenarios behaviour into the C++ program source simulate typical applications in real net- can easily be expanded. To make this code that is supplied. This enables you works, i.e. applications in the field of possible, the state model described in to simulate incorrect protocol behaviour, interoperability testing. the 3GPP test specification [4] has been for example. expanded to create a modular system. Future expansions include the HSDPA The versatile capabilities of the base standard, interfaces for stimulating a All actions carried out by macros of the unit are also reflected by the program- specific behaviour in layer 2, and a con- programming interface are written to a ming interface. The convenient use of IP- venient graphical user interface for inter- log file that can be decoded by the Mes- based data services (http, WAP, audio/ actively creating scenarios from existing sage Analyzer. This keeps you constantly video streaming, MMS) and video con- procedures. informed of what is happening – in the Stephan Sandhäger state involved and the scenario activity – in the lower protocol layers. You can also send information of your own to the log file while your scenario is running.

More information and data sheet at www.rohde-schwarz.com Tools and peripherals (search term: CRTU-W)

The generated programs run under REFERENCES Windows® 2000; the programming [1] 3GPP TS34.123: 3GPP Radio Access interface is integrated into Microsoft® Network – User Equipment (UE) Confor- VisualStudio .NET© IDE. User-cre- mance Specification [2] Protocol Tester R&S ® CRTU-W: Future- ated scenarios can be organized by proof tool for testing WCDMA termi- means of the TestSuite Explorer and nals. News from Rohde & Schwarz (2002) Project Explorer tools included in the No. 175, pp 4–7 R&S ® CRTU-W basic software. An exam- [3] 3GPP TS25.331: 3GPP Radio Access Net- work – Radio Resource Control (RRC) ple project is also supplied. Protocol Specification [4] 3GPP TS34.108: 3GPP Radio Access The MLAPI supports linking to the EMMI, Network – Common Test Environments for User Equipment (UE) Conformance enabling automatic control of the mobile Testing phone by means of AT commands [5]. It [5] 3GPP TS34.109: 3GPP Radio Access Net- also allows preliminary and final verdicts work – Terminal Logical Test Interface; to be output like in conformance testing. Special Conformance Testing Functions [6] Protocol Tester R&S ® CRTU-G/-W: 2 in 1: The above functions employ the same Software option for 2G/3G system sim- modules as those used in the TTCN test ulation. News from Rohde & Schwarz cases. (2003) No. 178, pp 22–24

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