1
An open service delivery platform for adding value to softswitch-based telephony environments Mosiuoa Tsietsi, Alfredo Terzoli and George Wells Department of Computer Science, Rhodes University Grahamstown, South Africa +27 46 603 8291
[email protected] {a.terzoli, g.wells}@ru.ac.za
Abstract— Softswitches have played a crucial role in next generation networks (NGNs) not only as the primary agents responsible for controlling the data and media paths between endpoints, but also as hosts of telephony applications such as billing and legal intercept. Even though very useful and flexible application interfaces have been used to program these softswitches, there is much benefit that can be derived from decoupling the application layer from the switching core. NGN architectures such as the IP Multimedia Subsystem (IMS) have borrowed the concept of an application server from the IT domain in order to deliver enhanced services to the network. This paper describes an initial investigation into the development of a service delivery platform (SDP) based on the JAIN Service Logic and Execution Environment (JSLEE) industry standard, to provide advanced services that can be deployed over a telephony environment called iLanga, which is based on the open source software PBX named Asterisk.1 Index Terms— softswitch, telephony, NGN, SDP, JSLEE
I. I NTRODUCTION The term softswitch is used to describe a software-based, distributed switching and control platform that manages the switching and routing of media packets between media gateways across a packet backbone [1]. The move towards performing such duties in software as opposed to hardware has made the softswitch more programmable and generally more flexible in its support for multiple protocols. As entities that can be in both the media and signalling path, telcos saw them as convenient points at which to host services by adding an application layer above the switching and call control layers. The resulting architecture, while useful and certainly powerful, leads to a monolithic design that is at odds with current trends in NGNs, where characteristically, there is a clean separation between the call control and application capabilities of network elements [8]. To enable these services elsewhere in the network, the use of a service delivery platform (SDP) has been used to provide a service creation and execution environment that can be used by network operators to provide new services to their clients. 1 This work was undertaken in the Distributed Multimedia Center of Excellence at Rhodes University, with financial support from Telkom SA, Business Connexion, Comverse, Verso Technologies, Stortech, Tellabs, Amotole Telecommunicaton Services, Mars Technologies, OpenVoice, Bright Ideas Projects 39, THRIP and the National Research Foundation.
II. T HE I L ANGA T ELEPHONY E NVIRONMENT iLanga is the name that was given to a complete, softwarebased PBX solution that was developed in the Computer Science department at Rhodes University, and is based entirely on open source software [5]. The main components of iLanga include the SIP Express Router (which is used as a stateful, forking SIP proxy), Asterisk (the popular software PBX, which can be considered a simple softswitch), Apache web server (which hosts the flash interface) and a proxy (for handling requests from the web interface and passing them to Asterisk). Service development in iLanga has been the topic of previous research [2], and there are also yearly contributions to the project as deliverables of the realtime communications postgraduate course in the department. New services targeted for Asterisk can be integrated into iLanga using three techniques: dialplan code, external scripts called AGI programs and special C programs that make use of the Asterisk application API. In the interest of using an external SDP to deliver services to iLanga, the above techniques could be used by the system to interface with an application server when an iLanga user requests a service. There are many candidate options for an SDP since many Internet content providers have recognised that there is an opportunity to deliver content and services to subscribers, by bypassing traditional telecom portals [4]. However, in identifying an appropriate solution for iLanga, two important factors must be considered: standards compliance and openness. The Mobicents implementation of the JAIN Service and Execution Environment (JSLEE) meets these criteria and is discussed in the next section. III. JAIN S ERVICE L OGIC AND E XECUTION E NVIRONMENT JAIN, or Java APIs for Intelligent Networks, represents an initiative within the Java world to provide programming interfaces to popular communication protocols. JSLEE is a Java standard produced through the Java Community Process [6] which makes extensive use of JAIN technology. It defines a component model for creating entities called service building blocks (SBBs) that are granular, reusable objects that can be used to compose complex services. For example a sophisticated multi-party video conference application may make use
2
of separate SIP proxy, presence and media management building blocks. JSLEE takes advantage of the abstraction provided by JAIN technology by allowing protocol connectors (called resource adapters in JSLEE parlance) to be plugged in to enable a convergence of multimedia services. To complement the JSLEE standard, a project called Mobicents was created that is currently the only JSLEE-compliant application server for the Java platform [7]. Resource adapter implementations for popular protocol stacks such as SIP and XMPP are provided by the project, as well as some example SBBs to assist developers. IV. E XPERIMENTAL D ESIGN Figure 1 shows the architecture of the proposed solution. The dotted boundary consists of the currently existing components in the iLanga environment. Outside the box is a proposed service directory which contains the location details of application servers and the services they host. The actual Mobicents installation will be located on the same internal network as iLanga. Similar application servers on external networks should also be listed in the directory and made available to iLanga users, as the figure also shows. When a user attempts a call in iLanga, Asterisk can use any combination of the methods described in section II in order to interact with the service directory, by making an appropriate query based on the incoming request. Once the service mapping has been made, Asterisk can then signal to the appropriate application server. As a multi-protocol environment, Asterisk will also be able to communicate with the server using the appropriate communication protocol (such as SIP, MGCP or XMPP) based on the nature of the user’s request. At the destination host, Mobicents receives the request as an event and uses an event router to pass control to the appropriate SBBs for execution. Some of the most active applications that are currently being hosted on iLanga include voicemail and prepaid billing. It will be possible to write discrete SBBs that will be hosted on Mobicents in order to provide these and other services to iLanga users. V. F UTURE W ORK There are various platforms for service creation and deployment for NGNs, however, it is not clear which platform is best suited for different scenarios. It is possible, for example, to combine several technologies such as JAIN, Servlets, Parlay and web services in a heterogeneous environment. Of particular interest, given the African context in which the research is being conducted, it is important to find the most appropriate and cost effective platform for service creation for developing countries. It would be beneficial to experiment with the various existing options to make a realistic recommendation. At Rhodes University a NGN testbed has been setup using the freely available OpenIMSCore software which implements the IP Multimedia Subsystem (IMS) call session control functions [3]. After the architecture in section IV has been developed and tested, the Mobicents server will be used as an application server for IMS clients, and we will be able to
Fig. 1.
Proposed service delivery architecture for iLanga using Mobicents.
compare our experiences with those gained during the iLanga integration. VI. C ONCLUSION There are benefits that can be derived from separating the service layer from the call control layer in softswitch environments like iLanga by delegating the service function to sophisticated application servers. Service delivery platforms such as Mobicents can be used as open, standards-based solutions for delivering new services in such environments.
Mosiuoa Tsietsi is currently reading towards a PhD degree in Computer Science at Rhodes University, Grahamstown George Wells is currently Head of Department of Computer Science at Rhodes University, Grahamstown Alfredo Terzoli is currently Project Director at the Center of Excellence at Rhodes University, Grahamstown
R EFERENCES [1] Lillian Goleniewski. Telecommunications Essentials. Addison Wesley, 2003. [2] Jonathan Hitchcock. Decorating Asterisk: Experiments in Service Creation for a Multi-Protocol Telephony Environment Using Open Source Tools. Master’s thesis, Rhodes University, 2006. [3] Fraunhofer FOKUS Institute. OpenIMSCore.org | The Open IMS Core Project. Available Online. URL: www.openimscore.org/. [4] Sumit Mittal, Dipanjan Chakraborty, Sunil Goyal, and Sougata Mukherjea. Sewnet -: A Framework for Creating Services Utilizing Telecom Functionality. In WWW ’08: Proceeding of the 17th international conference on World Wide Web, pages 875–884, New York, NY, USA, 2008. ACM. [5] Jason Penton and Alfredo Terzoli. iLanga: A Next Generation VoIPbased, TDM-enabled PBX. In SATNAC 2004 (Southern African Telecommunications Networks and Applications Conference), Spier Estate, Stellenbosch, 2004. [6] Java Community Process. JSR 22: JAIN Service Logic Execution Environment API Specification. Available Online. URL :http://jcp.org/en/jsr/detail?id=22. [7] Redhat. The Open Source SLEE and SIP Server. Available Online. URL :http://www.mobicents.org. [8] International Telecommunication Union. Definition of Next Generation Network. Available Online, November 2004. http://www.itu.int/ITUT/studygroups/com13/ngn2004/working_definition.html.
