Adding value to IMS multimedia telephony

Clearly separating value-added services Adding value to IMS multimedia telephony How service developers can focus on adding new value to IMS telephony for both users and operators without having to apply basic SIP. ROGIER NÖLDUS, MARTIEN HUIJSMANS, ANDERS RYDE AND JONAS FALKENÅ Multimedia communication s based on IMS and standards for multimedia telephony () provide support for voice-over-lte (VoLTE) and a basic set of telephony services. IMS/ make multimedia functions possible, so that users can add or remove services and callers during an ongoing communication session. For example, a user can start a communication session with messaging, complement it with voice or video, add or remove participants, send files, share pictures and more. A primer on IMS applications can be found in the IMS Application Developer s Handbook 1. On top of this architecture, operators can provide virtually any service that adds value for the user and takes their offering to the next level. The key to maximizing the potential of value-added services (VASs), and consequently revenue, is to create a clear separation between VAS, and the underlying IMS/ architecture, as well as an appropriate API between the valueadded service and this architecture. This new approach builds on the innovative use of existing protocols, such as SIP and Parlay X, and is an efficient way for operators to deploy valueadded services in an environment and support them in their efforts BOX A Terms and abbreviations 3G 3GPP A API AS AXE BCS BICC CAMEL CS CSCF DTAP EPC ETSI/ TISPAN Gm GSM 3rd-generation wireless telephone technology 3rd Generation Partnership Project reference point between MSC and radio-access for GSM access application programming interface application server Automatic Cross-Connection Equipment Business Communication Suite Bearer-Independent Call Control customized applications for mobile -enhanced logic CAMEL application part circuit-switched Call Session Control Function direct transfer application part Evolved Packet Core European Telecommunications Standards Institute/Telecoms and Internet Converged Services and Protocols for Advanced Networks reference point between and CSCF Global System for Mobile Communications gsmssf GSM service switching function HSS I2 I-CSCF ICS IFC IMS IM-SSF IN IP ISDN ISUP Iu LTE Ma Mb Mg Mr MRF MS Home Subscriber Server reference point between S-CSCF and MSC enhanced for ICS Interrogating CSCF IMS centralized service initial filter criteria IP Multimedia Subsystem IMS service switching function intelligent Internet Protocol IMS service control interface integrated services digital ISDN User Part reference point between MSC and 3G radio-access Long Term Evolution reference point between I-CSCF and SIP-AS reference point to IP services reference point between MGCF and CSC multimedia telephony reference point between S-CSCF and Media resource function controller multimedia resource function mobile station Multimedia Telephony NGIN P-CSCF SCP S-CSCF SDS Sh SIP SIP-AS SRVCC T UCIF VAS VCC VoIP VoLTE VPN WLAN Application Server reference point between CSCF and CSCF Ericsson Next Generation Intelligent Network proxy call session control function service centralization and continuity-as service control point serving CSCF service domain selection reference point between SIP-AS and HSS Session Initiation Protocol SIP application server single radio VCC Transaction Capabilities Application Part Unified Communications Interoperability Forum user equipment value-added services voice call continuity voice-over-ip voice-over-lte virtual private wireless local area

to maintain a leading position in mobile-communication s. FIGURE 1 in the IMS Background The IMS core provides communication connectivity among subscribers but, to match the service provided by legacy circuit-switched technologies, IMS needs to be complemented with a set of basic telephony services, on top of which a host of advanced real-time services can be added. The combination of IMS communication connectivity and these basic services is known as. is access-independent, meaning that it is compatible with all VoIP-capable IP-based access technologies, such as LTE in combination with Evolved Packet Core (EPC); Ethernet; and WLAN technology. An in-depth analysis of is available in an Ericsson white paper 2. Figure 1 provides a basic view of services in an IMS, showing only the most important reference points. The same core- architecture is used for all services in IMS, including value-added services. The and Ma reference points are the main interfaces for service logic in IMS. The reference point enables the serving CSCF (S-CSCF) to invoke a service when handling a SIP session. In this case, that service is an originating/terminating service, in a SIP application server (SIP-AS) which is based on initial filter criteria (IFC) forming part of the subscriber s IMS service profile. The IFC specifies the conditions under which the S-CSCF should invoke a service in a SIP-AS. All details required for the service invocation, such as SIP-AS address and service identification, are included in the IFC. The IFC is, if provisioned, received by the S-CSCF from the HSS during the registration of the subscriber in IMS. When a service in the SIP- AS is invoked, the SIP signaling is routed through the SIP-AS. The service logic has full control over the SIP session and requires support for SIP signaling and SIP state models. It can release the SIP session, create additional SIP sessions (such as for parallel alerting), establish a temporary SIP session with MRF for the purpose of playing an announcement to the user, or retarget the SIP session. All SIP messages for the SIP session are transmitted / Ma Gm IP access Gm CSCF Mr Mb Sh through the SIP-AS. Fortunately, SIP is designed so that new SIP headers can be introduced without affecting operational systems such as value- added services. IFC-based service invocation allows for service chaining: two or more IMS services or service components, residing in a single SIP-AS or in different ones, can be invoked sequentially from the S-CSCF. Two ways of augmenting Returning to the scenario in which is used for telephony, the reference point is specified for applying telephony as an application in IMS. Through the reference point, has full control over the SIP session and, as a result, over the multimedia telephony session. is therefore an intrinsic part of the provision of telephony. As mentioned, when telephony is enhanced with value-added services, the VAS itself should not have to handle basic call control, but rather the enhancements only. Two scenarios, shown in Figure 2 and Figure 3 respectively, apply for augmenting or enhancing with VAS. Chaining VAS and provides only limited capability to augment the session. It would be possible for the added service to control certain parts of the session by replicating the corresponding service and then adapting it to suit its specific requirements., however, builds on a complex state model of specified interaction between different supplementary services, making it difficult to break up the service while still conforming to requirements. In addition, the added service would need to access the profile (in ) and might HSS MRF Basic connectivity Multimedia telephony be affected by future extensions in the standard. The value-added service shown in Figure 3 could be an enterprise service such as Business Communication Suite (BCS) or another service deployed on the Ericsson Composition Engine on top of the Multimedia Telephony Application Server (). The service-logic invocation is essentially unaffected. The execution of the service logic follows the standardized process. At designated points in this service logic, the VAS can influence execution. The interworking between and the IMS core, including entities such as CSCF, HSS and MRF, is not affected. Figure 3 shows a clean separation between the core for telephony and the VAS layer. Again, the valueadded service interacts with to enhance the call; it does not apply basic call control. The VAS connects to through a northbound interface from (in this case the Parlay X protocol), rather than using the reference point. In this way, the service does not need to replicate basic call control. This is aligned with the concept of separating basic call control and value-added services in circuit-switched s. The approach also simplifies interoperability testing, as basic call handling is not affected by VAS implementation and vice versa. is becoming increasingly intertwined with advanced features such as IMS centralized service (ICS) and SRVCC. This is a further argument for the proposed architecture, which is designed to create an interface that is clear, isolating the core and

Clearly separating value-added services FIGURE 2 Augmenting by using IFC chaining Core for basic telephony Value added service layer Core for basic telephony its control layer from the service layer. The is a functional entity that facilitates the session centralization and session continuity (access transfer between LTE and 3G). The VoLTE standard is based on these standardized functional entities. To allow mass-market deployment of telephony over LTE, and are provided on scalable, high-availability telecom servers such as. The architecture in Figure 4 shows how VoLTE/ can be augmented with VAS from the BCS. Parlay X between and BCS provides the capabilities required for enhancing the multimedia telephony session. The value-added service, BCS in this case, uses Parlay X for tasks such as issuing notifications about actions including access or device transfer informing the BCS when, for example, the subscriber has changed from LTE access to CS access. S-CSCF FIGURE 3 Augmenting with VAS by using s northbound interface VAS Parlay X (SIP) S-CSCF VAS VAS protocol Control plane signaling for basic telephony The architecture shown here is, in principle, applicable to any value-added service, such as multimedia ringback tone and other such services in the Ericsson NGIN suite of applications, which can be deployed on the Ericsson Composition Engine. Integration of CAMEL services with Legacy services must be taken into account when integrating VAS with. In particular, a legacy IN service, specifically a CAMEL service, may need to be invoked for a multimedia session established in IMS. To benefit from the flexibility and power of IMSbased multimedia communication, a new breed of value-added service is required. However, to safeguard extensive investments in CAMEL service development and deployment, a methodology is required to utilize this investment during the transition period to an environment. The IM-SSF is a functional component for the application of legacy services in an IMS. A stand-alone IM-SSF is not suitable when deploying legacy systems in an IMS. Instead, the integration of a gsmssf within is recommended. The gsmssf then takes on the role of an IM-SSF (albeit not a stand-alone one). Figure 5 shows how an existing CAMEL service can be integrated with. The gsmssf component integrated with the execution engine exposes a standardscompliant interface to the legacy CAMEL phase 2 service. This minimizes the impact on the CAMEL service. Subscription data needed for invoking the CAMEL service from service execution forms part of the subscription data contained in the HSS. Invocation of a legacy VAS as depicted in Figure 5 can be combined with invocation of the legacy VAS directly from the GSM/3G core (not depicted) using the T relay method as described for dynamic service domain selection (SDS). The method shown in Figure 5 provides a clean separation between telephony ( in IMS) and value-added services (CAMEL). The legacy CAMEL service can then be used in combination with advanced IMS features such as SRVCC, including the enhancements provided in 3GPP Rel-10. These improvements include session continuity during the call-establishment phase and continuity of mid-call state by, for example, call-hold state. Handling VAS on IMS services over legacy access Value-added services can also be applied on IMS services over legacy access; the conceptual architecture is shown in Figure 6. The capability for VAS to control calls in the GSM/3G without anchoring the GSM/3G call in IMS will remain important for the foreseeable future (five to ten years). It allows operators to deploy (IMS, VoLTE) and benefit from the flexibility and power of nextgeneration VAS. This capability allows operators to continue to control calls in the GSM/3G (shown in Figure 6) and apply the same VAS. However, not all features of the VAS that are available

in the IMS will be available when the call is controlled in GSM/3G. For example, a feature such as call move, where the subscriber moves an ongoing call between their GSM phone and their SIP phone, requires the call to be anchored in IMS. This architecture also provides added value for operators in that it allows them the flexibility to determine the domain in which VAS should be invoked on a per-subscriber or per-call basis. Conclusions is the IMS standard that facilitates telephony, and it includes a defined set of basic services and supplementary services. Value-added services augment these basic and supplementary services, and must be clearly separated from the telephony when they are applied to. The interface needed between the VAS, and the IMS/ architecture needs to be well defined. 3GPP has specified, and continues to enhance, an extensive set of telephony services for the next-generation mobile, including advanced features such as VoLTE, voice-call continuity (VCC), session continuity and ICS. Specific functional entities in the IMS architecture are standardized and implemented in the Ericsson architecture. The separation of value-added services from is achieved through a services-specific northbound protocol exposure from. This approach has two advantages. First, functionality can be added to s extensive set of basic telephony and video services, combined with advanced services such as VCC. Second, service developers can concentrate on adding value to telephony rather than on controlling it. In addition to these benefits, using the Ericsson Composition Engine allows operators to provide VAS within the realms of and beyond. FIGURE 4 MS FIGURE 5 augmented by BCS A/Iu Usage of multiple terminals/multimode terminals Gm CS access + core IP carrier access I2/Mg CAMEL service integration with / Ma CAMEL service BCS Parlay X (SIP) CSCF Value added service Basic telephony including mobility, multi-terminal usage, address transfer, inter-terminal handover Legacy CAMEL, including subscriber data and backend system gsmssf service execution logic SIP adapter (SIP) Access Gm IMS core

Clearly separating value-added services FIGURE 6 Applying VAS for and legacy Enterprise logic T Relay BCS adapter Parlay X adapter (Parlay X) () MS DTAP CS access + core ISUP/BICC IMS core

Rogier Noldus joined Ericsson in 1996 and is an expert in architecture and protocols for multimedia. He has been involved in Intelligent Networks (IN) standardization and has driven the development of CAMEL within Ericsson. He made a switch to IMS and is now focuses on the integration of GSM and IMS s; covering Next generation IN, fixed-mobile convergence, media transmission, multi access, value-added services and next-generation core and access s. He holds a B.Sc. in electronics from the Institute of Technology in Utrecht in the Netherlands and an M.Sc. in telecommunications from the Witwatersrand University, in Johannesburg, South Africa. Anders Ryde is an expert in and service architecture at Business Unit Networks, Core and IMS in Sweden. He joined Ericsson in 1982 and has a background in and service architecture development for multimedia-enabled telecommunication, targeting both enterprise and residential users. He has been working on the evolution of IMS and IMS-based services for more than a decade, and is currently involved in the ongoing evolution of mobile telephony service and s to VoLTE. He holds an M.Sc. in electrical engineering from the Royal Institute of Technology (KTH) in Stockholm. Jonas Falkenå is an expert in IMS architecture and services for converged s at Business Unit Networks, Core and IMS at Ericsson in Sweden. He joined Ericsson in 1999 after studying computer engineering and business economics from KTH in Stockholm. He started out at wireline systems focusing on SIP and IMS solutions for the wireline market before working with IMS as a converged system. He has worked within several areas of IMS including integration and verification, system management, standardization, technical product management, and currently within portfolio management where he supports internal activities as well as technology lead responsibilities for key-customer solutions. Martien Huijsmans joined Ericsson in the Netherlands in 1989. He has an M.Sc. in mathematics from the University of Technology in Eindhoven, the Netherlands, and began his career by working with IN. Huijsmans was then involved in the development (on AXE-10) of the SCP, a service execution platform for IN applications. After this, he played a key role in the development of IN applications such as Freephone and Premium Rate, and the VPN enterprise application. He contributed to the first release of the Parlay gateway and Parlay gateway simulator. Huijsmans then spent several years in research projects, working on contextaware applications and mobility for business communication. Next he focused on the evolution of the existing VAS toward IMS, and VAS in the IMS service layer, particularly service composition and component-based and service-oriented architectures. In 2006, he was appointed an expert in service-layer solutions for application creation at Ericsson. He currently works with standardization for business communication in ETSI/ TISPAN, 3GPP and UCIF, in areas such as business trunking, hosted enterprise and visual communication. References 1. Noldus, Olsson, Mulligan, Ryde et al, IMS Application Developer s Handbook: Creating and Deploying Innovative IMS Applications, Elsevier, 2011. http://www.elsevier.com/wps/find/bookdescription.cws_home/725710/description 2. for Convergence, Ericsson white paper, 2010. http://www.ericsson.com/news/100709_wp_mmtel_244218600_c?