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Carrier Services
MSF proves IMS credentials in ‘real network’ trials
Architectural framework validates the role of the IMS core
by Roger Ward, President, MultiService Forum
The MultiService Forum develops implementation agreements (IAs) in order to promote interoperability between key NGN network components, both within a network and between networks themselves. In addition, the Global MSF Interoperability (GMI) program has provided the industry with a series of carrier hosted, globally networked test events, which are held every two years, to validate the various technologies covered by these IAs.
MSF Release 1, completed in 2002, covered the implementation of Media and Signalling Gateways. In 2004 MSF Release 2 introduced the concept of Softswitch and SIP Servers. And in 2006 MSF Release 3 dealt with the implementation of an IMS Core Network.
Figure 1. IMS core can be accessed using mainstream wireline and wireless access technologies.
In 2008, MSF Release 4 built upon this earlier work and addressed the key issues of fixed mobile convergence and end-to-end service delivery across a variety of disparate access technologies. In order to demonstrate the validity of the MSF’s approach, GMI 2008 focused on six networked, practical test scenarios that met the needs of real-world carriers. Access to an IMS core network was enabled over all mainstream wireline and wireless access technologies (see figure 1).
Six network test scenarios
The high-level Release 4 architectural framework visualized in figure 1 formed the basis for the six scenarios of the GMI 2008 event. The end-to-end IMS network is shown by the IMS core ‘hexagon’ and surrounding access technologies. Signaling and control for QoS is instantiated in the end-to-end IMS network. Specific applications such as IPTV build upon this foundation.
The six test scenarios were:
(1) End-to-end session control. The access technologies included baseband, broadband, 3GPP, 3GPP2, WiMAX, and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). Wireline / wireless convergence, nomadic (roaming) users, and PSTN and non-IMS SIP endpoints were tested to ensure backward compatibility with previous test results and real world implementations.
(2) End-to-end session control with QoS. This built on the scenario 1 tests.
(3) IPTV and two sub-scenarios. Conformance and interoperability tests for IMS-based IPTV as well as for the Alliance for Telecommunications Industry Solutions (ATIS) IPTV Interoperability Forum (IIF)-based IPTV. This was the first ever IMS IPTV interoperability event. It validated the potential for IMS as the basis for multimedia service convergence and also provided useful feedback to the IPTV standards effort.
(4) Location-based services. This test covered the capture of correct location information of an endpoint and its usage in such services as emergency calls and location-based routing.
(5) SOA gateway.This test covered the inclusion of Web-based applications in a service-oriented architecture over a converged SIP/IMS infrastructure.
(6) Management. This test involved the management of IPTV Set-Top Boxes plus the collection of IPTV-related statistics and off-line billing.
End-to-end session control
This is the foundation scenario and, as illustrated in figure 2, it was conducted over IMS core solutions provided by three different vendors. It demonstrated the ability of the IMS Core to simultaneously support a wide range of access network types and manage end-to-end session control across the different access network types. It also added the capability of the 3GPP defined ‘Transit Function’ network element and its capability to intelligently route calls from a peering network to a wholesale-IP user, PSTN user and IMS user.
Figure 2. End-to-end session control over three IMS cores and across seven access types.
Test objectives:
• Make end-to-end IMS calls between different access networks supported by the same / different IMS core networks.
• Make calls to other IMS users. 3GPP / 3GPP2 RAN vendors used RAN emulators and emulated UEs.
• Validate IMS roaming when an IMS user from vendor 1 roamed into another vendor’s IMS core.
• Demonstrate the priority handling of calls using the US Government-defined Resource Priority Header, which is part of the Government Emergency Telecommunications Service (GETS) standard.
• Demonstrate the 3GPP-defined Transit Function capability that enables the network operators to intelligently route calls from peering networks to IMS core / PSTN / other wholesale IP peering networks.
Key results
IMS protocols are generally mature and IMS products interoperate across Service Provider environments.
IMS products employing QoS enable an end-user experience that is superior to best effort Internet services.
IMS demonstrated the ability to provide a convergence platform for innovative services, e.g. IPTV. Although the IMS standards are mostly mature, the overall architecture is complex and important implementation choices have to be made to achieve full interoperability between vendors.
Looking ahead
The MSF is now focused on developing its Release 5 Architectural Framework, which will build on the lessons learned from GMI 2008. This release will focus on the inclusion of 3GPP LTE/SAE technology and highlight critical interactions with a converged NGN Core Network. The MSF is also working towards developing supporting scenarios and test cases for an MSF LTE/SAE Interoperability test event to be held in Q1 2010. This will focus on validation of the core network interfaces to ensure multi-vendor deployment strategies.
The test scenarios include LTE access into the Evolved Packet Core (EPC) network; roaming; non-LTE Access (e.g. GERAN/UTRAN) into EPC; handover/relocation; and access into the IMS core network in order to trigger QoS and utilize the 3GPP PCC (Policy & Charging Control).
Current plans are to host an LTE/SAE Interoperability test event in Vodafone’s Test and Innovation Centre in Dusseldorf, Germany. However, the event may also be expanded to include additional sites. China Mobile is expressing interest in providing facilities in Beijing, China.
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