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Notes from conference call on Open IMS Core - April 12, 2007

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  • From: "Candace Holman" <>
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  • Cc: "Weik, Peter" <>,
  • Subject: Notes from conference call on Open IMS Core - April 12, 2007
  • Date: Thu, 3 May 2007 17:04:13 -0400
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Notes from VoIP SIG + conference call on Open IMS Core - April 12, 2007
(Our unending thanks to Jeff Kuure for compiling the notes!  And thanks to Peter Weik for reviewing them and providing an updated link to the slides.)
Link to the Open IMS Core slides:

VoIP SIG Conference Call, April 12 2007




Dennis Baron, MIT

Chris Casswell, MCNC

Candace Holman, Harvard

Deke Kassabian, University of Pennsylvania

Jeremy George, University of Pennsylvania

Mike Parske  , Communigate

Jonathan Tyman, Internet 2

Dragos Vingarzan, Fraunhofer FOKUS

Peter Weik, Fraunhofer FOKUS





Today's call begins with Candace introducing Peter Weik and Dragos Vingarzan of Fraunhofer FOKUS. Both are working on PhDs in next-generation network topics, and today they will be discussing the Open IMS Core project.


The Open IMS Core is a reference implementation of IMS core network elements and used in testbed implementations of the IP Multimeda Subsystems architecture, which focuses on rapid service creation based on SIP and other internet protocols. The Open IMS Core is based on a collection of SER extensions, which form IMS proxies for different IMS session control functions and a user database. Candace notes that it should be familiar to anyone who has investigated SER in the past.


Peter's discussion is based on a series of slides. He begins by mentioning that he and Dragos are in the second generation of SIP developers at Fraunhofer FOKUS and by providing some background on the project. The main ideas behind IMS focus on network convergence based on IP technology. Peter discusses the challenges faced by those coming from a traditional telecom environment which was much more operator-based than newer IP networks. Network access is becoming more of a commodity, with flat rates for traffic and many services offered for free. These services are becoming the only differences between various networks. How users are affiliated with providers is also becoming important. One of the general ideas of IMS, according to Peter, is examining what can be done as network operators to mitigate these challenges.


The basic concept of IMS is that it operates in the session control layer to enable various features based on well standardized interfaces such as single sign-on, charging, QoS, signaling compression, presence and group management, and support for mobility. The IP network would be available to a variety of devices with common applications and services available to everyone.


Peter says that first specifications for IMS came about in 2000 within the 3GPP Rel. 5.  All the features of IMS are based on IETF existing protocols, with the initial development focusing on a mechanism for QoS and charging for IP services, as well as a way to provide secure communications. The idea was inspired by 3GPP, and is based on GPRS and UMTS networks. The Release 6 specs of 3GPP added QoS rules and enforcement, as well as PTT for cellular traffic. The current Release 7 added integration of fixed networks as well as wireless LANs. The next release, version eight, is starting to be defined now. Everything is based on IP protocols, including SIP for session control and Diameter for authentication and authorization and charging. Peter stresses that the project aims to use common, standardized protocols, and that IMS itself does not specify any services.


Dragos takes over and provides some background information on FOKUS, which is one of the 60 Fraunhofer institutes in Germany. FOKUS stands for Fraunhofer Institute for Open Communication Systems, and receives most of their funding from industry groups. There are currently 250 employees, and the group has been working on network convergence for over 17 years.


The Open IMS Core project is an open-source, GPL liscensed IMS core implementation. The project is based on SER, a high-performance, open-source SIP server which was also developed at FOKUS. SER is very flexible and easily customized with various extensions and a script-like configuration. The Open IMS Core adds three types of session control to SER - Proxy, Interrogating, and Serving CSCFs - which are enabled by loading extra modules. All other SER modules can be still be used at the same time. Dragos says that the development is in a constant state of flux and they can't always claim to be completely standards compliant.


Dragos describes a slide which illustrates what is added to a typical SER configuration to resemble an IMS network. Modifications include 3GPP specific extensions for subscription to registration events, authentication methods, and Diameter support for communication with a Home Subscriber Server. The Open IMS Core can dynamically trigger services on a per-user basis. The fourth component of the Open IMS Core, the Home Subscriber Server is based on MySQL and includes an embedded Tomcat server to provide web-based management. The Open IMS system operates by examining a SIP INVITE, using the CFCS to match certain criteria, and forwarding the request to a particular application server.


The OpenIMS Core project was launched at the second FOKUS IMS workshop in November. The event was successful, and another will be held in November this year. The project is under constant development, and is focused on providing a platform for IMS interfaces and for testing own components. It is intended to be used for proof-of-concept applications, as a testbed or reference implementation, or for testing commercial products. It is not intended to compete with commercial IMS implementations. Like many other technologies, IMS is covered by various patents. If you intend to use Open IMS commercially, there will likely be royalties incurred to the companies that hold patents for IMS.


The default installation of Open IMS should take roughly a half an hour, and is configured with two test users in an attempt to make it easy to get started. There arethree mailing lists devoted to the project where most interaction takes place. There are also no real releases other than daily snapshots, due to the dynamic development of the project. Documentation is also a major focus. The project aims to incorporate specifications from 3GPP Rel. 7 , as well as ETSI TISPAN and PacketCable 2.0.


Peter describes the goal of FOKUS group, which is to provide a "playground" for testing and experimenting with various technologies in the "Open IMS Playground" at Fraunhofer FOKUS. In terms of IMS, they have built an IMS test environment using their own developments and prototypes as well as best-of-breed carrier-grade components. They work closely with various partners on things such as media service and signaling gateways, and have close relations with various test tool vendors. Three use cases cited for the usage of the Open IMS Core as part of the Open IMS Playground are a collaboration with Deutsche Telekom focusing on community support, FMC services, and work on integrating IPTV signaling into IMS.


The first Open IMS Core based service was a converged voicemail system, which allowed users to call their voicemail from mobile or SIP phones. Calls could be monitored on a web interface and announcements could be customized. The second service was a network-stored address book, which could automatically sync contacts with various devices (including Outlook and today's mobile phones). More recent work has focused on building communities using presence, localization, and various other components. Other projects using the Open IMS Core are an IMS benchmarking effort, where Open IMS Core is used as a reference implementation due to the open nature of the project.


Peter summarizes his presentation by stating that he sees IMS as an interesting development, particularly in the VoIP domain. Like all open source software, he sees it as a way to stimulate interest in the IMS industry in a manner similar to how SER worked with SIP.


Candace asks about clients to use with the Open IMS Core. Peter says that the 3GPP IMS specifications call for complicated authentication based on ISIM cards, which other groups see as not mandatory. Open IMS therefore works with SIP MD5 authentication, so any SIP client can be used. All that is needed is IP access from any SIP client.


Candace asks about the speed of development. Peter offers an example of a SMS application gateway that was developed in half a day to trigger the sending of SMS to users authorized to make of the application. IMS allows you to direct messages to whatever application server you want, so the complexity of how they are handled is up to you.


Dennis mentions that many universities operate their own communications infrastructure, and asks about IMS interacting with such networks. Peter says that it is currently difficult to interoperate with older legacy networks without making use of media gateways or signaling gateways. He states that that today  many mobile network operators are testing IP networks at the edges, but they have no immediate plans to switch over to IMS. IMS allows you to negotiate and split between various components to build the network that you want.


Finally, Peter mentions that IMS is still mostly in a trial basis with operators. There is one commercial IMS network in Japan which launched last year and another one in China which was launched just recently, but overall it is still experimental with many operators. Yet, the IMS architecture is accepted with many standardization groups worldwide as the blueprint on how to offer SIP based multimedia services for network operators in the fixed, mobile and cable network domain.




  • Notes from conference call on Open IMS Core - April 12, 2007, Candace Holman, 05/03/2007

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