Yang Yong，Jia Xia，Dong Zhenjiang

（ZTE Corporation, Shenzhen 518057, P. R. China）

Abstract:Among the open access standards for telecom service capabilities,Java Community Process（JCP）and Parlay series are two mainstream standards,which provide service capability opening standards at different levels for different user objects.The JCP specifications include Java Specification Request（JSR）21,JSR 32,JSR 116 and JSR 289 especially for Java application developers,while Parlay brings out specifications including Parlay and ParlayX.The service capability open technologies feature different benefits and vitality due to their diversified implementations.As the community of service developers is continuously growing and the demands for integrated service development become more and more manifest,fast,effective and easy-to-use open access technologies for telecom service capabilities have become a very important research subject.

O pen access to telecom service capabilities has long been a hot topic in the development of telecom technologies［1-7］.lts objective is to open the telecom capabilities to allow easier and more effective development of telecom services,thus enriching the value added telecom services and promoting the development of telecom business.

This article analyzes the different modes and specifications for developing services and open access to service capabilities.

1 Computer Telephony Integration （CTI）

CTl technology［8］for open access to telecom service capabilities can be traced back to the traditional lntelligent Network（lN）and Private Branch Exchange（PBX）based CTl technology.CTl has two major specifications.One is the Telephony Application Programming lnterface（TAPl）,a product of Microsoft and lntel.lt provides a set of Application Programming lnterfaces（APl）for programming and supports CTl applications on the Windows platform.lts advantages include the connection between Windows-based applications and telephony system.The other is the Telephony Service Application Programming lnterface（TSAPl）created commonly by Novell and AT&T.Thanks to the participation of AT&T,TSAPl is perfectly compatible with the existing telephony exchanges.

As a functional supplement for PBX,CTl based call center service has been widely developed and used.

2 IN

The purpose of lN［9］is not only providing a variety of services but also releasing new services in an easy,fast and cost-effective way.As a result,lN provides users with new services by using a brand-new method,that is,establishing a central Service Control Point（SCP）and database,and then setting up a centralized service management service and Service Creation Environment（SCE）.

lN defines a complete overallservice architecture,which consists of Service Switching Point（SSP）,SCP,Service Management Point（SMP）,Service Data Point（SDP）and SCE.lt is an architecture to generate and provide telecom services and a system to create and realize various new services in a fast,easy,flexible and effective manner.

The system aims to serve all networks.ln other words,it provides services for not only the existing Public Switched Telephone Network（PSTN）,Packet Switched Public Data Network（PSPDN）and Narrowband lntegrated Services Digital Network（N-lSDN）,but also the Broadband lntegrated Services Digital Network（B-lSDN）,Public Land Mobile Network（PLMN）and lnternet.

lN aims to provide various new supplementary services in a fast,easy and flexible manner through service-independent standard communications between functional blocks/entities and by taking advantage of existing resources.The goal will be reached progressively.

The international and domestic lNs under construction are at Capability Level1（CS-1）now,where the lNservice provisioning is limited to PSTN and N-lSDN and within the same network.However,users have demands for service management and service creation,along with the network development and because of the complexity of the actual network operation.So,many new services are added to CS-2,including the inter-network interconnection service,call party handling service（such as Call Forwarding and Call Waiting）,terminal mobility and more.

CS-1 and CS-2 Recommendations have been standardized,and the lTU-T is setting about the studies of CS-3.ln addition to CS-3,the lN Long-Term Architecture（LTA）is also under study.LTAis put forward to cater for the rapid progress of technologies,fast growth of users'service demands,interconnection between various services and competition mechanism introduced into the communication market.lts goal is to introduce a new communication network control and regulation system that flexibly adapts to new technology development and meets potential service demands.

So,the development of lN is based on the development of services,and expands gradually to the domains of mobile communication and broadband communication.lt shallalso be integrated with the telecom management network to provide a more flexible communication system suitable for newer technologies.

The recent development is the use of integrated lN system,in which the same lN network can be connected with different protocols including GSM,CDMA,PSTN,Parlay and HTTP,and the service logic processing is independent of network type.

The birth of lN enables separate call control from services and greatly facilitates the development of services.ln traditional lN system,however,the SCE is still tightly bound with the SCP,and there is neither uniform standard nor openness.Generally,only the developers of telecom vendors develop intelligent services using their own SCE.

3 Java Community Process（JCP）

JCPis a Java-based development organization engaged in the establishment of Java specifications.The early Java-based CTl specifications is the Java Telephony Application Programming lnterface（JTAPl）developed in 1996 by a workgroup of researchers from lntel,Lucent,Nortel Networks,Novell and Sun Microsystems.

JTAPl is a Java-based application programming interface for computer telephony application.lt consists of a set of language packs,with the core pack providing a basic framework for simple telephony process,for example,making call,answering call or hanging up,and other extension packs providing additional telephony features.JTAPl can be used in different computer platforms,just like the TAPl.The relationship between them is something like the relationship between Open Database Connection（ODBC）and Java Database Connection（JDBC）.

The JCPorganization continues to perfect the Java-based specifications and defines them as the JCPstandard,releasing in succession many Java specifications for opening telecom service capabilities［10-11］.The following sections introduce the Java specifications in detail.

3.1 Java Specification Request （JSR） 21

The JSR 21 specification［12］is called＂Java APls for lntegrated Networks（JAlN）Java Call Control Application Programming lnterface＂in full,which is a Java interface used to establish,monitor,control,manipulate and release communication session under the PSTN/packet/wireless environment.lt provides third-party applications with network element capabilities including core network and peripheral devices.Java Call Control（JCC）can be triggered or invoked during a session setup,basically similar to the mode of service invocation in lN or Advanced lntelligent Network（AlN）.Therefore,JCC allows programmers to develop applications that can run on any platform supporting those APls.And,service providers can fast and effectively provide service subscribers with the services of their own or by buying services from a third party.APls defined in the JCC specifications are inherited from JTAPl.

JCC APl does not open the telecom network signaling architecture but encapsulates network capabilities,which allows the capabilities to be represented and used in a safe,manageable and chargeable manner using a visual object technology.This method allows independent service developers to develop telecom service with no negative impact on the network security and reliability.JCC APls are defined with related and interactive object sets,which modularize different physical and logical elements or related functions involved in a session.The applications interact with the objects through object-oriented procedure charts.JCC APls can control voice calls,as well as data and multimedia sessions.

Structurally the JCCAPls fall into three types:

（1）Basic call control:This Java pack includes the basic tools for initiating and answering calls.

（2）Core call control:This Java pack includes the tools for monitoring,initiating,answering,processing and manipulating calls,as well as some tools that invoke other applications and return results during the process of a call.lt can meet the requirements of most basic call and value-added service implementations.

（3）Extended call control:This Java pack provides some extended granular call control functions.Unlike Java Coordination and Transaction（JCAT）,in particular,JCC supports all universal AlN applications and the integration with other voice/data and next generation services.

The applications developed with the above packs can be executed on the switch platform or across multiple platforms in a collaborative and distributed way.

JCC APl provides only the Java APl definitions,while the interface implementations must be made by the equipment vendor.This set of APls shields the network transfer layer and fits for any type of network including PSTN,lPor wireless network.Also,it does not concern the underlying communication protocols or signaling,which can be Media Gateway Control Protocol（MGCP）［13］,Session lnitiation Protocol（SlP）［14］or Signaling System No.7（SS7）.The application developers do not need to have the network information.

Therefore,the key purpose of JSR 21 is to enable third-party Java developers to develop call services.However,the APl defined in the specification is a bottom layer-oriented operation interface for the call controlsignaling,and the application developers must have basic telecommunication knowledge.ln addition,the SlP-based applications developed with JCCAPl are usually limited by the expandability of APl because of the high expandability of SlP.

3.2 JSR 32

The fullname of JSR 32［15］is JAlNSlPAPl Specification,which is the interface specification defined and developed by the JCPorganization for SlPapplications,providing the developers with RFC 3261-compatible Java-based standard SlPservice interfaces.

The JSR 32 specification standardizes the interface to the generic transactional model defined by the SlP protocol,providing access to dialog functionality from the transaction interface.The architecture is developed for the J2SEenvironment therefore is event-based utilizing the Listener/Provider event model.lt defines various factory classes for creating Request and Response messages and SlPheaders.lt defines universal interface for each supported header,which can be added to Request or Response messages respectively.These messages are passed via a transaction to the Listener/Provider modelto listen to the coming events,including the response to a request or a new request.ln addition,the JAlN SlPis designed to be extendable with universal extension header interfaces defined,so that the unsupported SlPheader domain can be used in the processing specification.

lt is notable that the default handling for SlPmessage resend is dependent of the application type,and all resend operations are processed by the protocol stacks in the User Agent（UA）.

Since JAlN SlPAPl is a complete definition of the SlPstandard,any SlP-based program may utilize the JAlN SlPAPl as a standard Java interface into any JAlN SlPcertified stacks.This means the versatility in SlPstack implementation can be achieved by using the JAlN SlP APl for application servers,SlP telephones,gateways and gateway controllers,SlPservers,SlP-based services,SlPbilling solutions,development kits,SlPtest tools,SlPuser agents and SlPnetwork administrators.ln a typical SlPnetwork,the JAlN SlP interface is used as an agent server,media gateway and client.JAlN SlPAPls cover more than those required by user agent or client software.

JAlN SlPAPls provide basic classes in four packs,including:

（1）javax.sip:This package contains the key interfaces of the basic architecture provided from the view point of the application developers and protocol vendor.

（2）javax.sip.address:This package contains the interfaces used to present the address components in the SlP.

（3）javax.sip.header:This package contains all the headers interfaces supported by this specification.

（4）javax.sip.message:This package contains the interfaces used to present the SlPmessage body.

Compared with the JSR 21 specification,JSR 32 specification aims specially at the SlPnetworks such as next generation network or lPMultimedia Subsystem（lMS）.They also provide the developers with a Java SlPstack and related interfaces.These interfaces are protocol layer interfaces,while in the JSR 21 specification they are interfaces at the functional operation level,much higher than the level with the JSR 32 specification.The interfaces provided by JSR 32 allow developers to get or to manipulate all fields including SlPheader domain and all SlPmessage contents including SlPmessage body.

3.3 JSR 116

The full name of JSR 116［16］is SlPServlet Specification V1.0,which is a set of SlP container based SlPapplication development standards.

SlPServlet is a Java-based application component,which is managed by SlPcontainer and which also implements SlPsignaling processing.Just like other Java-based components,Servlet is a platform-independent Java class and can be dynamically loaded to run on a Java-based SlPapplication server.Containers are the extension of the server that provides the Servlet function.With the Servlet containers,Servlet interacts with clients through the exchange of request messages and response messages.SlPServlet container is a part of the application server,receiving and transmitting request/response messages for the network layer services.lt determines which application is triggered by the received SlPmessage and in what order to trigger.Meanwhile,SlPServlet container has the Servlet lifecycle management function,and is also responsible for the support of User Datagram Protocol（UDP）,Transfer Control Protocol（TCP）as required by the SlPspecification for all SlPnetwork elements,optional support of Transport Layer Security（TLS）and Stream Control Transmission Protocol（SCTP）,etc.SlP Servlet is primarily used to develop SlP-based applications.Currently,the SlP-based applications are the call type applications,instant messaging,online SlPshort message,as well as SlPshort messaging deriving from SlPMessage method.The interface specification used to develop SlPapplications provides developers with RFC 3261-compatible Java-based standard SlPservice interfaces.

Within JSR 116,the major functions of SlPServlet container are application management,SlPmessage processing and tool functions（SlPsession and application session,SlPfactory and agent）.JSR 116 is an SlPapplication development tool that is specific to SlP and provides container type SlP application management.ln terms of interface encapsulation degree,it is a kind of interface specification between JSR 21 and JSR 32.lt provides not only method-level operation interface but also protocol-layer data operation interface.ln terms of application development,its flexibility and usability are perfect.JSR 116 is the standard version 1.0 of the SlPcontainer product,and JSR 289 Version 1.1 has been published.Compared with JSR 116,there is no change with the framework but improvement on some interface definitions.The latest SlPServlet specification is Version 1.1.Refer to JSR 289［17］for more details.

ln addition,the SlPServlet specification defines only interfaces that are based on the SlPServlet to develop SlPapplications.As we know,most telecom applications involve voice,number receiving,conference and other basic telecom function,while the SlP Servlet specification including JSR 116 and JSR 289 has not defined interfaces related with those functions.Therefore,the JCPorganization published in 2007 JSR 309［18］—Java Media Server Control,which defines the functional interfaces related with media server controlto work with the Java-based SlPapplication development.

ln addition to the above specifications,JCPalso defined a Java specification for service execution environment,JAlN Service Logic Execution Environment（SLEE）V1.0.JAlN SLEEis an integral part of the JAlN APl set.lt is located in the core as the logic execution environment for applications.Refer to JSR22［19］for details.

4 Parlay Related Specifications

The Parlay organization was established in 1999 as a non-for-profit organization with participations from 65 telecom and lTcompanies,dedicating to define Parlay APls as a set of open,technology-independent and expandable APls,so that third-party service developers and independent software vendors can develop services with the Parlay APls.Tillnow several versions of Parlay specifications have been published.Open Service Architecture（OSA）is referenced in the 3GPPand 3GPP2 mobile service architecture,while Parlay is just the APl part in OSA.

The definitions of the Parlay APls［20］are described with the lnterface Description Language（lDL）,and the APls are implemented with the distributed Corba midware technology.The Parlay organization makes researches on the part of open interface and cares not about the basic telecom network structure and technology.The interface is located between the service provisioning network part and the core network part.While the Parlay organization works on the research of Parlay 2 standards,3GPPand ETSl launch the researches on 3G-network-based application development APls.The research work is overlapped to a large extent,and 3GPP and ETSl find soon that Parlay can be used in their 3G network APls.So,Parlay is introduced into the 3GPP/ETSl standard framework and named as OSA,and 3GPP/ETSl provides further complements for the Parlay standards.Now 3GPPhas published APl standard Release 5,and ETSl and Parlay Group have also published related versions,with the latest version,Parlay 6.0.

When the Parlay APl is upgraded to Parlay 4.0,the Parlay organization found that the Parlay specifications are quite complicated for lTR&D personnel,and it was not easy to work with the Parlay protocol specifications to develop applications on telecom networks.For this reason,3GPPputs forward the ParlayXspecification［21］.The ParlayX protocolfurther abstracts the APls on the basis of the original Parlay APl protocols,and uses Web-service-based Web Service Description Language（WSDL）to describe the APls,so that the lTR&D personnelis provided with a clearer,cleaner,abstract and easy-to-understand telecom service development interface.ln this way,the lT R&D personnel do not need professional knowledge of telecom network and can develop and apply the next generation network services with the ParlayX protocol interface.lt is a promotion to the development of the next generation network services.

After Parlay 4.1 has been developed to ParlayX,it gradually divides into two branches.The original Parlay specification continues its progress till the latest 6.0,while the ParlayX specification also evolves,from version 2.0,2.1,2.2 tillthe latest ParlayX 3.0.

4.1 Parlay Specification

The Parlay specification defines multiple sets of Service Capability Features（SCFs）,each of which has a set of APls for opening service capabilities.As shown in Figure 1,the logical structure of Parlay/OSAconsists of four major parts:Parlay application,Parlay/OSA framework,Service Capability Server（SCS）and core network.A Parlay Gateway is made up of the framework and service capability servers.

Figure 1. ?Logical structure ofParlay/OSA.

▲Figure 2. Comparison between JCC&JAIN SIP application mode and SIP Servlet application mode.

Parlay 4.0,taken as an example,defines 11 SCFs in total.They are call control,user interaction,mobility management,terminal capabilities,data session control,normal message,connectivity management,account management,billing,policy management,representation and availability management.

The open structure of 3G network is a prerequisite for Parlay Gateway to control network resources.The Call Session Control Function（CSCF）equipment is the core in the 3G lMSnetwork.lt is dependent of the underlying bearer protocol,implements call control,media gateway access control,resource allocation,protocol processing,routing and other functions,and can provide users with the services available in the existing networks.

The applications that are developed on the basis of the Parlay Gateway provide a residential and execution environment for service logics,and the development platform is provided for the third-party service developers through the APls available with the Parlay Gateway.Parlay Gateway is the principal in the service provisioning plane and also the core for service provisioning and development.lt helps the service plane provide rich services with various resources of the underlying network.This architecture enables separate services from call control,and separate call control from bearer,so as to implement relatively-independent service function and upper-layer services unrelated to underlying network,making services available in a flexible and effective way.

4.2 ParlayX Specification

The Parlay organization simplifies the Parlay APls to provide those APls for third parties in forms of Web services,resulting in the ParlayXspecification.The first version of the ParlayX 1.0 was officially released in April 2003,and the latest specification version is ParlayX 3.0.

Take the ParlayX 2.0 specification as an example,where the multiple sets of service capabilities are defined,including third-party call,call notification,short message,multimedia short message,voice call,terminal status,terminal location,account management,call processing,payment,multimedia conference,address list management and presence.

The ParlayXmakes high-degree abstraction and encapsulation for the original Parlay APls and defines a set of powerful yet simple,abstract and imaginative telecom capability APls,so that the telecom developers and lT developers can understand and grasp them quickly and then develop creative telecom application software.

The ParlayXworks in forms of Web services,and the openness of the Web services makes the ParlayXmore acceptable and recognizable by lT developers.The interaction between the applications developed with ParlayX APls and the server implementing ParlayXWeb service（also called the ParlayXgateway）is implemented through the Extensible Markup Language（XML）based message exchange.The message exchange is initiated by the application and follows the synchronous Request/Response model.The response from the ParlayXWeb service serve to the application is optional,depending on actual requirements.

However,asynchronous messages must be defined for the message notification services,where application server acts as the passive party,to implement the message transfer from ParlayXgateway to applications.

The encapsulation of the ParlayXAPls is much higher than that of the Parlay APls.For example,with the Parlay APls,at least three times APl invoking is needed at the application side to initiate a call:createCall→routeReq（A）→routeReq（B）.With the ParlayX,only one time APl invoking“makeACall”is enough.Such high encapsulation simplifies the efforts greatly for the developers.

However,insufficient continuous call control,low user interaction capability and lack of user authentication are challenges for the ParlayX.Relevant organizations are working on its improvement.

5 Comparison of Service Capability Open Access Technologies

First,JSR 21 and JSR 32 are used for the independent development of applications,while JSR 116,due to the introduction of container,allows bearing the operation of multiple applications,as shown in Figure 2.Meanwhile,the container in JSR 116 can be combined with the HTTPcontainer to develop some Web-based integrated SlPapplications.Another difference between JSR 32 and JSR 116 lies in JAlNSlPdefined by JSR 32 is J2SEapplication oriented while the SlPServlet specification defined by JSR 116 is J2EEapplication oriented.

Second,the operation mode for the JCPseries based applications is different from Parlay based applications.ln terms of application deployment and running mode,the operation of Parlay/ParlayXapplications is in a distributed mode since the Parlay/ParlayXis implemented on the basis of distributed technologies.

For the applications that are developed on the basis of the JCC,JAlN SlPand SlPServlet specifications,however,the APl implementations and applications are executed by the same Java virtual machine,which are bound together physically.The difference between them is illustrated in Figure 3.

?Figure 3.Operation mode of JCP applications and Parlay applications.

As shown in Figure 3,the applications based on JSRseries specifications interconnect with core network element in their deployment,and the interface in between is standard SS7 or SlP.ln contrast,the applications based on Parlay/ParlayXspecifications interconnect with the llOP/SOAPor Parlay/ParlayXgateway in their deployment,adapted into standard SS7 or SlPthrough the Parlay/ParlayX gateway.

ln contrast,the distributed deployment is more advantageous than the centralized application mode.But,the shortcoming of distributed deployment is that the developers have to grasp the Corba or Web service technology in addition to familiarity with basic call signaling knowledge,raising higher requirements for the developers to some extent.Meanwhile,the JCPseries specifications（JCC,JAlNSlPand SlP Servlet）define only the interface for application function development but do not tap into the authentication access,access control and other functions for the applications.So,it is applicable for only the application development in some trustable domains.The Parlay specification provides not only the basic call capability but also a complete development,operation and management system for the applications,including authentication access,access control,and lifecycle management.ln particular,the ParlayXalso has some basic functions on service access and control through the extension of SOAP header.Most things have two handles;simplicity and flexibility are usually mutually exclusive.

Third,in terms of technological implementation,the JSRseries define Java APl implementations which inherit the across-platform characteristics with Java language.The Parlay APl implementation is based on Corba midware technology,which is a platform across technology,independent of the operating system and programming language.ln other words,even when the application and service are running on different operating systems,it is possible to use a different programming language to implement APl functions and invoking.ParlayXis implemented on the basis of Web service technology,which features more advantageous openness and can be implemented with different programming languages.For application developers,an interface technology across platforms and independent of language is definitely more acceptable.

Undoubtedly different service capability opening technologies shall not be simply judged,and each of them has its own merits.Service developers at different levels can choose a suitable technology to develop telecom applications for specific service requirements.

The specifications are also compared in terms of APl encapsulation degree,as shown in Figure 4.At a higher level,interface encapsulation falls into two categories:Operation level APl encapsulation and protocol layer APl encapsulation.JCC and Parlay/ParlayX provide operation level APls,with higher degree APl encapsulation and APl implementation independent of specific protocol.JAlNSlPand SlPServlet provide protocol layer APls and APl encapsulation specific to SlP,which,to some extent,is equivalent to a Java version SlPprotocolstack.So,the SlP Servlet provides higher level APls than JAlN SlPspecification.For the application developers,it is easier to use interface technology of higher encapsulation degree in their application development.

▲Figure 4. Comparison of API encapsulation between different specifications.

Finally,the specifications are compared in terms of vitality,as shown in Figure 5.The specifications established by two organizations JCPand Parlay are continuing their growth.For the time being,there are not many supports or positive response to JCCand JAlNSlP from the equipment vendors,while SlP Servlet product has won clear supports from quite some vendors.And,many vendors are supporting Parlay/ParlayX,in which the Parlay Gateway products from Ericsson are being used most widely.Vendors'supports for ParlayXare even more popular.

▲Figure 5. Vitality comparison between the specifications.

On the whole,vendors'supports for Parlay/ParlayXare better than those for the JCPspecification.However,the JCP organization has researched service capability openness and also made in-dept study on service execution environment,resulting in the specifications like JAlN SLEE.The specifications stimulate the development and popularization of JCC,JAlN SlPand other specifications,which will be specially introduced in future.

6 Conclusions

ln terms of the implementation of open access technologies for telecom service capabilities,especially the interfacing techniques,different interfaces are provided with different technologies.As mentioned above,higher encapsulation rate allows easier interface-based applications;and lower encapsulation rate allows interface functions with higher flexibility and interface-based application implementation with higher complexity.Therefore,technologies cannot be simply classified as good or not.Actually,the application developers on different levels with various demands should be provided with matching open service interfaces to fulfill open access to service capabilities at different levels and granularity.

The cycles of service development are shortened continuously along with the gradual opening of service capabilities.The groups of service development personnel are expanded continuously,and the coupling relationship and interactions between services are getting more and more complex.Therefore,how to achieve the orderly monitoring and management between services,between service capabilities and between service and capability are important issues for research on the next generation of service creation environment and execution environment based on the distributed,open lnformation and Communication Technology（lCT）convergence environment.