Network Protocol Interoperability Testing based on Contextual
Contents
1. Connect entails the sending of the PDU Invoke to the network In other words this invariant controls that a transaction related to the connection es tablishment is initiated by the WTP initiator layer and transmitted through the network to its corresponding distant entity to perform the requested service The simple invariant is described as follows I1 TR invoke req pdu 2 false TID Invoke TID Invoke TID 2 The parameter value TID which is instantiated in the messages TR Invoke req and Invoke allows to warranty that the infor mation sent to the network are those of the initial request of the service The invariant represented by the signature sign 02 checks that the transaction related to the client connection is taken in charge by the WTP Responder activated by the event RevInvoke It also checks that the transaction realizes the requested service by sending the PDU Result to the network The second invariant is described as follows 2 Invoke TID 2 RevInvoke TID 2 x TR Result req Result TID false The two invariants are connected by means of the identifier of the transaction TI D The value of this parameter permits identifying the transactions that are performed by the distant layers and allows to follow the requested service These invariants are checked on the correlated traces as previously explained Two correlations are needed i one is performed be tween the traces of WTP2. M Mackaya and P Laurencot A multi service and multi protocol validation platform experimentation results In TestCom 2004 Springer 2004 7 J Gadre C Rohrer C Summers and S Symington A COS study of OSI interoperability In Computer Standards and Interfaces pages 217 237 1990 8 N Griffeth R Hao D Lee and R Sinha Integrated System Interoperability Testing with Applications to VOIP In FORTE PSTV 00 Pize Italy October 2000 9 S Kang and M Kim Interoperability test suite derivation for symmetric communication protocols In FORTE PSTV 97 1997 10 Kannel foundation Kannel Overview http www kannel org overview shtml 11 D Knuth J Morris and V Pratt Fast pattern matching in strings SIAM Journal on Computing 6 1 323 350 1977 12 O Kon and R Castanet Test generation for interworking systems In Computer Communications volume 23 pages 642 652 Elsevier Science 2000 13 J Orset B Alcalde and A Cavalli A formal approach for detecting attacks in ad hoc networks International Journal of Network Security 22 141 149 2007 14 Y Park M Kim and S Kang Conformance Testing of Multiprotocol IUTs In The IFIP 12th IWTCS Budapest Hungary September 1999 15 V Paxson The Bro 0 8 User Manual ICSI Center for Internet Research March 2004 16 O Rafiq and R Castanet From conformance testing to interoperability testing In The 3rd Int Workshop on Protocol Test System
3. algorithm described by the figure 1 is to correlate the events observed by the trace TRAC Etrans with the PDU ob served in the trace TRAC Enetwork This in order to constitute a new trace TRAC Erans Which is an end to end one The PDU ob served in the network is considered as input or output depending on the direction of the communication messages and is consequently used in this way by the interoperability invariants In the following we provide an explanation of the correlation algorithm For each input 7 and or output op of the TRAC Etrans denoted by the external while loop we check that it belongs to the PDU SET_PDU set specified as an input of the algorithm inside the first external if This set of PDU names can change accordingly to the protocol to be tested If the current input ix or output ox second external if belongs to the set SET_P DU then we look forward in the TRAC Enetwork for the packet identified by the name of the PDU and its TID using the function getPacket If the packet is not found in the TRAC E Network instruction if pck null with the required event i e 7 or ox then we have a correlation error This error could be produced by the loss of a packet or by an erroneous behaviour in the transaction layer In this case the correlation process is stopped fault_correlate true On the other hand if the packet is found in the trace we add the information included in the packet to the trace TRAC Ej ans ini
4. of Observation PO It is necessary to observe the messages exchanged by the distant entities A sniffer is used to collect the traffic carried by the communication medium For the communication protocols area there are several sniffers avail able such as Ethereal Wireshark 19 new release of Ethereal and Snort 17 We install points of observation at the interface levels of the protocol layer to be tested These local observers are needed to perform vertical interoperability between protocol layers at dif ferent levels For horizontal interoperability the sniffer is used to collect the protocol messages that are exchanged between distant entities In the testing architecture used we have local observers that collect the messages at the protocol layer interface Further more the architecture relies on a global observer that reconstructs a global trace from the trace retrieved by the local observers and from the PDU exchanged at the communication level In this work we consider the horizontal interoperability between two entities To achieve the construction of the global trace i e an end to end trace we correlate the events that are collected by the different ob servers The correlation is feasible because of the specific nature of communicating protocols We assume that we have all the required information on Service Data Units SDU and also the correspond ing PDU Once a global trace is reconstructed we can check an end to end p
5. AC E trans TRAC Erans TRAC Etrans k 0 fault_correlate false while k lt n and not fault_correlate do begin case of a correlation with an entry of TRAC Etrans if ik E SET_PDU then begin selection of the parameter TID for the entry iz Ap Pi p name trans TID selection of the corresponding packet peck getPacket ix p value if pck null then fault_correlate true else begin entry of a couple of PDU trans and session input_pdu pck trans_pdu pck session_pdu We append this entry in TRACE vane with respect of the format of input output needed to apply the invariants TRACE tnans k 1 0k 1 input_pdu ix ik Ok ik 1 0k 1 end end case of a correlation with an output of TRAC Etrans if 0 E SET_PDU then begin selection of the parameter TID for the output Ok Ap Pop p name trans TID selection of corresponding packet peck getPacket o p value if pck null then fault_correlate true else begin output made of a couple of PDU trans and session output_pdu pck trans_pdu pck session_pdu we append this output in ITRAC E ans With respect of the format of input output end end k k 1 end if fault_correlate then return false else return T RAC E trans Figure 1 Correlation algorithm of protocol events session of the packet pck General idea of the algorithm The aim of the
6. ATED WORKS Many works address the problems of interoperability testing There are mainly two kinds of approaches those that are based on a formal framework and those based on experimental results The authors of 16 have proposed a solution for interoperability test generation Their work is based on the generation of the reachabil ity graph of the communicating system Kon and Castanet in 12 have formalized the relation of interoperability by adapting the ex isting conformance relations 9 proposed algorithms to generate a test suite that are based on stable states of their composition algo rithm Previous works can be classified as methods based on reach ability analysis that often suffer from the well known state space explosion problem when applied to realistic or real case studies Methods based on experimentations have also been proposed such as 18 but they lack a formal framework 8 based their work on interoperability by proposing a test gen eration technique from the joint behaviour of end users interfaces This method avoids the combinatorial explosion problem by classi fying the edges concerning interoperation as black edges and those concerning local activities as white edges They propose an effi cient algorithm to retrieve the significant transitions in other words the black edges 4 proposed to consider transitions on a communi cating graph representing interactions between distant entities and they have develo
7. Network Protocol Interoperability Testing based on Contextual Signatures and Passive Testing Fatiha Zaidi 1Univ Paris Sud LRI Orsay F 91405 2CNRS Orsay F 91405 Fatiha Zaidi ri fr Categories and Subject Descriptors C 2 2 Computer Communication Networks Network Proto cols Routing protocols D 2 5 Software Engineering Testing and Debugging Testing Tools 1 6 Simulation and Modeling Model Validation and Analysis General Terms Design Reliability Verification Keywords Interoperability testing contextual signatures passive testing com munication protocols WAP ABSTRACT This paper presents a methodology for interoperability testing based on contextual signatures and passive testing with invariants The concept of contextual signature offers a framework to add informa tion on the states the values of parameters as well as logical con nectors that increases the expressive power of invariants This al lows expressing horizontal and vertical interoperability properties i e between layers of a protocol stack or end to end communica tion between distant entities In order to test interoperability we have defined a correlation algorithm between the events collected from different network views client or network side Once the correlation has been performed we apply the contextual signatures that characterize interoperability properties to check their validity To illustrate the application of the propo
8. btained the Inconclusive verdict This is because of the length of the traces that were too short We have adjusted the length to avoid this problem We also obtained such verdict for a contextual signature related to push primitives We cannot observe such primitives initiated by the gateway since no subscription of provider has been done The results obtained have established the correct interoperation of two entities regard ing the test objectives based on the expert requirements Invariant SITGI SIG2 STG3 STG4 Time 3 15 2 60 3 19 1 15 Verdict Pass Pass Pass Pass Table 1 Verification of horizontal interoperability signatures on traces 6 CONCLUSIONS AND FUTURE WORK In this paper we have presented a new methodology for inter operability testing that improve previous approaches and advances the state of the art The use of contextual signatures eases the ex pression of interoperability testing properties Two types of inter operability properties vertical and horizontal may be described by contextual signatures These are very useful to respectively check interoperation between layers of the same protocol stack and check that distant entities of the same layer can interoperate Another important contribution of this work is the definition of a correlation algorithm This last enables the application of pattern matching to check the correctness of execution traces with respect to interope
9. cify a property that combines several invariants i e several individual signatures Hence the signatures can be connected by logical connectors The structure of this element is defined by several attributes as follows e logic connector indicates the link between the current signature and the one specified by the attribute id sign re quest We can use a conjunction and or a disjunction or to define this link e id sign request identifies the signature that will be re lated to the current signature 3 6 Correlation algorithm This section presents the correlation algorithm We introduce first the notation used and secondly we give the general idea of the algorithm which is described in detail in figure 1 Notation used by the algorithm The traces collected by the local observers at the protocol inter face levels of a client or server side are represented as a succession of inputs and outputs The inputs and outputs represent services primitives SDU events representing the PDU reception or emis sion or events related to timers The function getPacket allows identifying from the trace TRACE Network the packet where the PDU transaction corresponds to an event observed in TRAC Etrans indicating the reception or the emission of this PDU The correspondence is established by the name of the message and the parameter TID The function returns the correspond ing packet to be used by the algorithm of the figure 1 If t
10. d information on the Platonis platform The experiments were carried out on traces of more than 1000 mes sages We have defined several contextual signatures related to con nection establishment SIG1 corresponding to the signature of the properties exhibited by figure 2 of a mobile client connection es tablishment with a PDA SIG2 a page download of the mobile client SIG3 and disconnection requested by the PDA SIG4 We have performed experiments with several clients to observe dif ferent TID parameters For sake of simplicity we just give the results for these four signatures see table 1 Note that the time in seconds second row corresponds to the time obtained on a Mi crosoft Windows XP Pentium IV 800mMHz with 2Go of RAM We have also checked on the specification the soundness of the invariants enclosed in these contextual signatures We were able to perform such verification because the formal description of the WAP protocol the client and the WAP server was available in the frame of the PLATONIS project Numerous experiments have been performed They are related to the connection establishment with the different level of trans port class i e 0 1 or 2 that conditions the number of messages exchanged between the distant entities We have tried different val ues for the parameters of the messages We have also tested the interoperation based on the data transfer and disconnection phase In some of the experiments we o
11. e mentation For the specification in 3 we have developed algo rithms which are better with respect to complexity than classical algorithms for model checking These algorithms are usually ex ponential on the number of transitions In our case the proposed algorithm possesses in the worst case a complexity that is linear with respect to the number of transitions in the specification if the invariant does not contain the wild character The complexity is quadratic if the symbol appears in the invariant For the verifi cation of the implementation we have developed a new algorithm that checks the properties on the real implementations traces This algorithm is based on classical algorithms for pattern matching on strings see e g 11 and 5 It possesses a complexity O m n in the worst case where m and n are respectively the length of the trace and of the invariant Let us remark that in most practi cal cases the length of the invariant is several orders of magnitude smaller than the length of the trace Thus we may consider that the previous complexity is almost linear with respect to the length of the trace 3 5 Concept of contextual signatures Contextual signatures are defined by a XML eXtensible Markup Language tree This representation has been chosen because it contributes to structure the signatures and to define the syntax of the data XML also offers means to check the syntax of a document through a DTD Data T
12. entation under test which is an advantage when it is necessary to test a system with no direct access to their components The case study presented here is a good illustration to perform vertical interoperability i e between proto cols layers no direct access to the embedded layer is given also for end to end interoperability it is not always possible by using active testing techniques to have a global view of the communication be tween the entities of the system In our case we can observe what occurs at each entity side and to obtain a global view through the correlated traces To illustrate the suitability of our approach a real case study is presented the Wireless Application Protocol WAP To perform the experiments a free software protocol stack has been installed namely Kannel version2 10 The paper is organized as follows In section 2 related works to the context of the research are presented Section 3 gives the defini tion of interoperability testing interoperability testing architecture and an outline of the proposed methodology This section also in cludes the definition of invariants and contextual signatures that are used to describe interoperability properties Section 3 6 presents the correlation algorithm to produce end to end traces The appli cation of the proposed approach and the experimental results are exhibited in section 5 Finally section 6 gives the conclusions and perspectives of this work 2 REL
13. he packet is not retrieved in the TRAC Enetwork then the correlation fails We consider that for each event observed in TRAC Etrans which entails the sending of a PDU we have to observe this PDU in TRAC ENetwork In the same way an event observed in TRACE trans corresponding to the reception of a PDU has to be observed in TRAC Enetwork If this is not the case an error has occurred either caused by the loss of the PDU or by due to an erroneous interoperation behavior between the entities The events that are used by the algorithm i e inputs and outputs are associated to their parameters A transac tion trace of an entity is represented formally in the following way TRAC Etrans 11 Piz 01 Por in Pin On Pon Where e ix Op are respectively the inputs and outputs such that 1 lt k lt n e Di pi Pm is a vector which is characterized by a finite set of variables and the values of the parameters of the input ip We note p name and p value the corresponding access to the name and value of parameter p with 1 lt j lt m We use the same notation for outputs i e Po p1 p The boolean variable pck marked in the function below is used to mark the packet that has been already retrieved from the trace The variable pck trans du is explained below 4 ALGORITHM CORRELATION With respect to the traces captured by the sniffer these must be processed as described previously transformation validat
14. ine emits output o and moves to the state s Intuitively a trace such as i1 01 n 1 On 1 5 tn O is a sim ple invariant for M if each time that the trace 71 01 in 1 On 1 is observed if we obtain the input in then we necessarily get an output belonging to O where O C O In addition to sequences of input and output symbols the wild card characters and are al lowed where the wild card character represents any single sym bol and the represents any sequence of symbols This notion of invariant allows us to express several interesting properties For example by using the invariant we can test that an user is discon nected each time he requests a disconnection I req_disconnect disconnected The idea is that each occurrence of the symbol req_disconnect is followed by the output symbol disconnected An invariant that expresses a property as if y happens then we must have that x had happened before is called an obligation invariant Obligation invariants may be used to express properties where the occurrence of an event must be necessarily preceded by a sequence of events For example the intuitive meaning of an invariant such as I request_page req_ack page_sent is that if the event page_sent is observed in the trace then we must have that a page had been requested before and that the server has acknowledged the reception of the request Invariants can be checked on the specification and on the impl
15. ion for matting In this way we obtain a succession of packets each one integrating the PDU transaction and session exchanged between the two distant entities The formal representation of a network trace has the following form TRACENetwork pcki pcku where pck is a packet such that 1 lt i lt u which the structure is composed by the cou gt gt ple trans_pdu ptrans and session_pdu Psession They char acterize respectively the PDU transaction and session and their associated parameters or when the session layer is not solicited only the PDU trans_pdu Ptrans and its associated parameters gt Ptrans pi Pzx and Psession pi Py are vectors which characterize respectively a finite set of parameters vari ables for the PDU transaction and for the session One can ac cess the parameters as explained in p By adding session layer information to enrich the expression of our invariants one can ex press properties related to services primitives and to PDU We note gt pck trans_pdu pirans and pcki session_pdu Psession respec tively the access to the PDU trans_pdu Ptrans and session_pdu Inputs TRAC Etrans i1 Piz 01 Po lt gt n Pin On Pon TRACENetwork pcki peku SET_PDU e g for the WAP SET_PDU Invoke Result Ack Abort Outputs false indicates the failure of the correlation or returns the new built trace TR
16. ped two algorithms to cover such transitions All these works are based on an active testing approach where the tester has the ability to stimulate the implementation under test IUT and verify whether the output obtained for each input is ac cording to the specification When the tester is not provided with a direct interface to interact with the IUT passive testing is better adapted than active testing for performing conformance and inter operability testing For these reasons we consider here the use of passive testing techniques Even though passive testing techniques are not new see for example the approach shown in 2 in the last years a very active research on passive testing has been developed The passive testing approach proposed here is based on invariant analysis in which the invariants are properties the IUT is expected to satisfy It is inspired by a previous work 6 which concerned mainly conformance testing 3 The difference with the work pre sented here relies on the introduction of contextual signatures that permit to express interoperability properties This was not possible by using only conformance requirements Moreover the testing ap proach proposed in 3 is based on local observations while in the work presented in this paper a correlation mechanism is provided to obtain a global trace that is needed to test end to end properties The concept of contextual signatures describes in a structural way a set of pro
17. perties that involves different communication ele ments The concept of signature is inspired from the system Bro 15 that is a Network Intrusion Detection System NIDS In our case contextual signatures are extended to provide information such as dependence between invariants constraints on the variables and also the notion of state Moreover this concept provides a structure to specify the requirements related to the interoperability between different protocols implementations 3 PRELIMINARIES 3 1 Interoperability definition In the following we provide the definition of vertical and hori zontal interoperability that we consider Definition 1 Horizontal interoperability layers of the same level of distant entities are interoperable if they successfully pass the con formance tests and if it can been shown that together they satisfy the level N service as specified by the standard 7 Definition 2 The multi protocols or vertical interoperability 14 focuses on the interoperability between layers of the same protocol stack Performing this test is important in order to warranty that the protocol layer will correctly interoperate with the other layers of the protocol stack 3 2 Interoperability testing architecture The testing architecture is based on a more accurate level of ob servation in order to establish a diagnostic regarding the implemen tation behaviors This is the reason the architecture relies on the set up of Points
18. rability properties defined as contextual signatures This algorithm has been implemented in the TESTINV software tool and applied to a real protocol i e the WAP We plan to continue our work on contextual signatures and pas sive testing in the field of network security The techniques on pas sive testing we have developed 13 have shown to be well adapted to detect anomalies attacks and intrusions However this past work presented some limitations needed to reduce the number of false positives The use of contextual signatures in this framework could help refine the analysis and reduce their number 7 REFERENCES 1 I 9646 1 Information Technology OSI Conformance testing methodology and framework Part 1 General Concepts 2 J Ayache P Azema and M Diaz Observer A concept for on line detection of control errors in concurrent systems In 9th Symposium on Fault Tolerant Computing 1979 3 E Bayse A Cavalli M Nunez and F Zaidi A passive testing approach based on invariants application to the wap In Computer Networks volume 48 pages 247 266 Elsevier Science 2005 4 C Besse A Cavalli M Kim and F Zaidi Automated Generation of Interoperability Testing In TestCom 2002 pages 169 184 Berlin 2002 Kluwer Academic 5 R Boyer and J Moore A fast string searching algorithm In Communications of the ACM pages 762 772 1977 6 A Cavalli A Mederreg F Zaidi P Combes W Monin R Castanet
19. res The XSL expressions constructed to filter information or perform data formatting can be easily adapted to different types of trace sources Step 5 Syntax checking Once the traces are filtered they are checked through a DTD Data Type Definition procedure that validates the structure of the file containing the filtered network traces Step 6 Traces correlation Finally the validated traces are cor related The algorithm for the correlation of the traces is de scribed in detail in the section 3 6 Step 7 Verification of the contextual signatures on the traces Once an end to end trace is obtained by applying the correla tion algorithm the verification of the interoperability proper ties is performed and a verdict is emitted Pass Fail or Incon clusive This last step is based on the application of pattern matching algorithms as mentioned in subsection 3 4 These algorithms have been adapted to check contextual signatures 3 4 Invariants definitions Two kinds of invariants are defined the simple and obligation invariants The simple invariant can be defined as follows Let M S T sin O Tr be an FSM An FSM is defined by a finite set of states a set of input actions a set of output actions an initial state Sin and a set of transitions Tr Each transition t Tr is a tuple t s s 2 0 Intuitively a transition t s s i 0 indicates that if the machine is in state s and receives the input 7 then the mach
20. rizontal protocol interoperability and end to end interoperability This requirement is of a crucial importance to obtain a successful integration of communication components in telecommunication systems In this context conformance testing alone is not sufficient to guarantee successful communication between different components The reason is that this kind of test is only devoted to checking the behaviour of a component in relation to its specification The ISO 9646 standard 1 mentions that conformance testing can increase the probability of interoperability but cannot guarantee the suc cessful interaction between different implementations It must be noted that conformance testing is a necessary step to insure inter operability but it is not enough It could still be possible that com munication components do not communicate correctly even if each conforms to the same standard Until nowadays the majority of research works on interoperabil ity testing are based on active testing that implies interferences with the implementation under test The main objectives of the work presented in this paper is to propose a methodology for interop erability testing based on passive testing which is innovative and original To the best of our knowledge no work based on passive testing techniques has been applied to perform interoperability test ing Furthermore the originality of our approach is based on the absence of interference with the implem
21. rnitiator and the network traces captured by the sniffer ii a second one is realized between the traces of WTPResponder and the network Using our TESTINV tool the in variant defined by the signature sign O is applied on the traces of the first correlation The invariant with the signature sign 02 is ap plied on the traces of the second correlation This property holds if both invariants return a Pass verdict as the two invariants are con nected by a logical connector i e an and Client WAP Gateway WSP WTPinitiator WDP WDP WTPresponder WSP Transaction of level 2 Network TR Invoke req pdu connect TID Invoke TID __Invoke TID2 Inve a RevInvoke TID 2 re Sha __ Pee Fa TR Result req P Ka Result TID false Simple invariant of the signature sign 01 ae _ Simple invariant of the signature sign 02 Figure 2 Horizontal Interoperability Property 5 3 Experimental Results Contextual signatures have been applied to communication traces between several types of Wap clients i e a real mobile phone a PDA Personal Digital Assistant or a mobile simulator and a spe cific server We have used the defined POs that have been added at the interface layers of a PDA and of the simulator for the client side The server side has also been logged on We have used an open source WAP stack i e the Kannel stack version 2 Inter ested readers can refer to 6 for more detaile
22. roperty using the concept of contextual signatures 3 3 Outline of the proposed methodology As mentioned previously to perform interoperability testing end to end traces have to be constructed in order to verify the expected interoperability properties To achieve this the following steps need to be performed Step 1 Properties formulation The properties are retrieved from the standards and expressed the main requirements related to the communication with distant entities Step 2 Properties as contextual signatures Properties have to be formulated by means of contextual signatures Contex tual signatures have to be conform to their Data Type Def inition DTD The verification is done automatically by a parser These signatures enclosed simple or obligation in variants that expressed local properties i e related to a local entity To represent interoperability properties the contex tual signatures are used to connect the invariants by logic connectors All the information presented in the section 3 5 are also furnished Step 3 Extraction of execution traces from local observers by means of a sniffer installed on each side entity The traces are in XML format Step 4 Transformation of traces in an adapted format Traces are transformed by the application of filtering rules defined by a XSL sheet These rules hold the network information needed to perform the checking of the properties described by the contextual signatu
23. s 1990 17 Snort An open source network intrusion prevention and detection system http www snort org 18 G Vermeer and H Blik Interoperabillity testing Basis for the acceptance of communication systems Theory and practice In Protocol Test Systems VI C 19 North Holland 1994 19 Wireshark An award winning network protocol analyser http www snort org
24. sed approach a real case study is proposed the Wireless Application WAP protocol The results of the experimentation performed on this protocol are also presented 1 INTRODUCTION Produces the permission block and copyright information For use with SIG ALTERNATE CLS Supported by ACM Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page To copy otherwise to republish to post on servers or to redistribute to lists requires prior specific permission and or a fee SAC 09 March 8 12 2009 Honolulu Hawaii U S A Copyright 2009 ACM 978 1 60558 166 8 09 03 5 00 Emmanuel Bayse St ria T l com F 97782 Issy les Moulineaux Emmanuel Bayse steria fr Ana Cavalli Telecom Sud Paris CNRS SAMOVAR F 91011 Evry Cedex Ana Cavalli int evry fr Future communication networks in particular those based on In ternet lead to the emergence of new families of protocols and ser vices for telecommunication systems These systems will have as infrastructure heterogeneous networks which need to be inter connected and to interoperate while preserving the required qual ity of service They will be confronted with interoperability prob lems between protocol variants and services including vertical and ho
25. tially TRAC Etrans If we consider i then the information of the packet is an input of the trace TRAC Ej ans and ip becomes an output instruction else i e TRAC Etrans tk 1 Ok 1 input_pdu ix ik Ok ik 1 0k 1 If we consider ox then the information of the packet is an output of the trace TRAC Etpans and ox becomes an input This part is treated in the second external if denoted in the algorithm by case of a correlation with an output This procedure is repeated until the trace TRAC Etrans is com pletely covered or a correlation error has been found In this way an end to end trace TRAC E ans is obtained on which interoper ability contextual signatures can be checked 5 APPLICATION TO THE WAP This section presents the application of the proposed methodol ogy to a real case study the WAP protocol We also present an example of horizontal interoperability property and give the exper imental results 5 1 The Wireless Application Protocol WAP Wireless Application Protocol specifies an application framework and network protocols for wireless devices such as mo bile phones pagers or PDAs Personal Digital Assistant One of the main objectives is to bring Internet content and advanced data service to these devices WAP is composed of several layers the topmost of which is the Wireless Application Environment WAE that offers a framework for the integration of the different Web and mobile telephony appli cations Ne
26. xt comes the Wireless Session Protocol WSP which offers to the WAE layer two types of services connection or con nectionless In the first case a session oriented service can be provided supporting session initiation suspension and resumption The connectionless services are on top of a transport datagram ser vice which can be provided either by a Wireless Datagram Service WDP or by UDP User Datagram Protocol The session oriented service is provided on top of the Wireless Transaction Protocol WTP This protocol is a confirmed transaction protocol that is a light weight version of TCP 5 2 Interoperability signatures This section presents an example of horizontal interoperability invariant which is expressed by contextual signatures using the grammar that was described in section 3 5 The interoperability properties to be checked on the traces are defined in XML and re spect the structure of the DTD We do not exhibit vertical interop erability property for the sake of space Figure 2 presents a property that checked that the layers WTPrniti ator and WTPResponder dedicated to the transaction management interoperate correctly to perform a connection establishment The figure is decomposed on two simple invariants that are enclosed in the two signatures The invariant with the signature sign O checks that a connection request received by the WTPrnitiator received after the primitive TR Invoke reg and the parameter pdu
27. ype Definition The validity of a document in our case a signature can be checked with a parser The DTD can be changed accordingly to the protocol that we consider we can change the list of possible values for some attributes We will not go through all the details of the contextual signa tures We will only present here the key elements of this new struc ture Nevertheless we can mention that several elements defined by the info proto element allow adding information on the pro tocol that is being considered The invariant definition presented above is enclosed in the content element which characterizes the property to be tested The content element is described by two attributes one that indicates the type of invariant i e simple or obligation and another that formally describes the property using regular expressions see section 3 4 The contextual signatures have also a context element that integrates the implementation s contextual information In partic ular we add state information This knowledge will help analyze the trace for obligation invariants Indeed with this element we can set the state from which the invariant will be checked The attribute current state indicates the state that the implemen tation needs to go through in order to check the invariant making it a kind of pre condition to be checked The dependency element is used to define relationship with sev eral signatures In other words it allows to spe
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