IMS (IP Multimedia Subsystem) enables and drives efficient converged service offerings. It is the key to delivering multimedia services with telecom-grade quality of service across fixed and mobile accesses. It creates new opportunities for operators who want to deliver attractive, easy-to-use, reliable and profitable multimedia services – including voice, pictures, text and video, or any combination of these – with existing services. Users benefit by being able to enjoy attractive converged multiple services regardless of access network and device. Service success is very much dependent on the ability of operators to create and deliver an experience that fulfills or exceeds users’ expectations. To maintain their position as service provider, operators need to climb up the value chain and take a more active part in service delivery.
IMS is designed precisely for that purpose. IMS is access-independent: it is the only open standardized way to deliver IP-based consumer and enterprise services, enabled by one common core and control, to the fixed, mobile and cable communities. It combines the quality and interoperability of telecoms with the quick and innovative development of the Internet. IMS does this by making the unique values of the telecom industry easily available to the application development community. When implemented according to agreed standards, IMS enables operators to mix and match equipment and applications from multiple vendors, and enables mobile users to access their personal set of services wherever they roam, whichever operator network they are connected to. IMS includes the tools and functions needed to handle numerous non-standardized services in a standardized way – ensuring the interoperability, access awareness, policy support, charging, security and quality of service functionality required to meet consumer demand for attractive and convenient offerings. Essentially, application servers are implemented above the standardized IMS architecture. IMS is developed to interwork with existing networks.
This overview describes an IMS architecture designed to meet the needs of telecom operators in the new converged multimedia environment. The Call Session Control Function (CSCF) and the Home Subscription Server (HSS) are the essential nodes in the IMS system. The control signaling routed by the CSCF is the IETF Session Initiation Protocol (SIP). The HSS provides the user profile database to manage user authentication and authorization for the subscribed services.
SMS is one of the top strategic questions for any operator these days. There are many good answers, but perhaps the key one is that IMS delivers innovative multimedia services over fixed and mobile networks using open standards. IMS addresses key issues such as convergence, service creation and delivery, service interconnection and open standards. IMS can allow an operator to retain its existing business models, or evolve towards new ones.
Open IMS Standards Interworking
To ensure mass-market acceptance, IMS services need to work across different networks, devices and access technologies. This is enabled through standards-compliant IMS products, verified in an end-to-end environment through interoperability testing between device and infrastructure vendors. The IMS standard (illustrated in Figure 3) defines a generic architecture to offer multimedia services, including Multimedia Telephony. It is an international, recognized standard, first specified by the 3GPP/3GPP2 and now being embraced by other standards bodies such as ETSI/TISPAN, CableLabs, JCP, OMA and WiMAX Forum.
The IMS standard supports multiple access types, including GSM, WCDMA, CDMA2000, cable, wireline broadband access, WLAN/WiFi and WiMAX. IMS takes the concept of layered architecture one step further by defining a horizontal architecture, where service enablers and common functions can be reused for multiple applications. The horizontal architecture of IMS enables operators to move away from traditional vertical ‘stovepipe’ implementations of new services – eliminating the costly and complex traditional network structure of overlapping functionality for charging, routing and provisioning. Standardization makes it work end to end and enables an attractive, convenient user experience.
SIP Application Server
All the applications and services in IMS are executed in SIP application servers. One SIP application server can be dedicated to a single service or host several services. In IMS, it is also possible to combine services from several different SIP application servers to create one unified user experience for the end-user. For instance, a user can from a single terminal application, simultaneously combine the services of presence and video calling although the services themselves are located on different SIP application servers. The main benefits of SIP application server technology are ease of application development, rapid network and centralization. By centralizing business logic on an individual or small number of SIP application servers, updates and upgrades to the application for all users can be guaranteed. There is no risk of old versions of the application accessing or manipulating data in an older, incompatible manner.
Key Network Protocols in the IMS Network
The following are protocols supported by Primal Technologies in our service offering:
SIP is the main signaling protocol used in IMS networks. It was developed by the IETF and was selected by 3GPP as a standard for IMS in Release 5. The function of SIP is to establish, modify and terminate multimedia sessions – with medias such as voice, video and chat – over IP networks, where the media delivery part is handled separately. In SIP there is just one single protocol, which works end-to-end and supports the establishment and termination of user location, user availability, user capability, session set-up and session management. SIP is also designed to enable additional multimedia sessions and participants to be dynamically added or removed from a session. These are the major reasons SIP has been selected in IMS; it is also considered to be flexible and secure.
Diameter, a development of the current RADIUS protocol, was chosen as the policy support and Accounting, Authentication, Authorization (AAA) protocol for IMS. Diameter is used by the S-CSCF, I-CSCF and the SIP application servers in the Service Layer, and in their exchanges with the HSS containing the user and subscriber information. Compared with RADIUS, Diameter has improved transport – it uses Transmission Control Protocol (TCP) or Stream Control Transmission Protocol (SCTP), and not UDP, as transport – resulting in improved proxy, enhanced session control and higher security.
H.248 is a control protocol used between media control functions and media resources. Examples of nodes with media control functions are the Media Gateway Control Function (MGCF) and Media Resource Function Controller (MRFC). Typical media resources are the Media Gateway and Media Resource Function Processor (MRFP).
Internet Protocol version 6 (IPv6) is a network-layer IP standard used by devices to exchange data across a packet-switched network. It follows IPv4 as the second version of the Internet Protocol to be formally adopted for general use. Originally, IMS was specified to use IPv6; however, with 3GPP Release 6, IMS does provide support for IPv4 and private address scheme. This means that even though IMS is expected to drive the adoption of IPv6, it is not dependent on IPv6 availability in order to be successfully launched.
Where Primal is Going
From the very beginning, Primal Technologies’ Open Services Environment had been architected to support different access types including wireless, landline and cable companies. As LTE is the common upgrade path for both CDMA/1X/EVDO and GSM/UMTS wireless operators, Primal Technologies OSE-IMS architecture has similarly evolved to be deployed in virtual public or private environments in order to take advantage of IMS functionality and messaging requirements, with no data migration necessary, and also ensuring that an operator can continue to support 2G/3G CDMA and GSM messaging within the same network -- and with other roaming partners.
New LTE-Only operators also reap the benefit of a comprehensive set of feature functionality, interfaces and web screens that have already been developed for 2G/3G and 4G LTE wireless operators. The Primal Technologies Online Charging Service (OCS) and Policy and Charging Rules Function (PCRF) continue to support 3GPP DIAMETER charging sessions over the Gy/Ro and Rf interface in the latest 3GPP releases. Immediate, Event and Session charging scenarios with/without rating are all supported. The Primal SMSC includes the IP-SM-GW module to support messaging with IMS clients on various phone models, and interfaces with the SCC AS and HSS, while simultaneously supporting MAP/IS-41/SMPP messaging conversion between CS and IMS domains. Primal Visual Voicemail has been widely deployed in various operators’ IMS networks for several years supporting SIP Call Control, and Message Waiting Indication and today also supports AMR WB codes for high definition VoLTE calls. In the situation where the existing Carrier Billing system may not support a SIP interface but where Real-Time VoLTE charging is a requirement - the Primal Technologies Real-Time Signaling Gateway (RTSG) actively converts SIP calls to DIAMETER sessions for charging with 3rd party billing servers.
Primal Technologies has the background and experience to implement any service use case brought forward by any LTE IMS operator that may require a new IMS Application Server (AS) functionality.