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October 2007 | Volume 2 / Number 5
Feature Articles

The Road to IMS: What Service Providers Need to Know

By Amit Chawla
Initial discussions on the IP Multimedia Subsystem (IMS) began in the early 2000s, initially as an evolutionary path for mobile operators from their GSM/WCDMA-based networks. Very quickly however, wireline operators realized the benefits of IMS and the technology is now seen as appropriate to all telecoms operators.

For wireline operators the vision of IMS is that it will enable them to migrate their decades-old, circuit switched networks to all IP in a single bold step. But existing networks are not coherent entities, they have evolved incrementally over the years. Within a single network there will be a mixture of new and legacy protocols and equipment built using different generations of specifications and utilizing a multiplicity of interfaces and providing a range of specifications. This reality undermines the claims of some vendors' solutions that IMS can be easily and seamlessly implemented using a 'box- based solution'. IMS solutions, architected correctly, can be implemented in networks containing multiple application servers supporting multiple devices, legacy TDM and early VoIP network elements, as well as early IMS implementations. What operators need are flexible solutions that will enable them to support the legacy elements of their networks and their existing users whilst migrating their networks to IMS. Unfortunately, at present, the majority of vendors pushing IMS do not have the capabilities to offer carriers the flexible solutions they require to integrate such diversity of network offerings.

To disguise this lack of flexibility in the solutions they are offering, vendors are trying to persuade operators to agree to a single solution, or box-based implementation, one usually compliant with an outdated generation of specifications.

This approach freezes the network at a particular moment in the evolutionary cycle and does not allow future development as new technologies and specifications come on stream. It also means that only customers with devices compliant with the frozen specification can be supported, those with older or newer devices are somewhat restricted. As it is totally unrealistic to expect users to replace their devices at the behest of the operator, rather than through choice, operators must decide whether to abandon a large number of their customers or remain locked into a solution which will not enable them to innovate for the foreseeable future.

To avoid being trapped operators must develop an IMS strategy which is sufficiently flexible to allow them to migrate their networks in line with technological developments whilst continuing to equally support their legacy and new customers. Most importantly, operators need to determine whether the expertise of their incumbent suppliers is sufficient to meet and overcome the differing challenges of the migration to IMS and rapidly embark on an applications based revenue stream.

At the present time the majority of IMS vendors lack the flexibility and range of skills required to smoothly evolve telecommunications networks to IMS. Ensuring full connectivity for every existing and potential user and device, for example, requires expertise in protocol mediation possessed by few vendors. The vendor needs to have knowledge of legacy technologies at one end of the scale and the very latest 3GPP IMS specification developments at the other. Every network will have its own unique mix of new and legacy protocols and technologies so the vendor needs a huge skill set and the ability to respond flexibly to the different demands of different networks. Protocol 'translation' is not the answer. Instead, choosing the right vendor is the first step on the road to successful migration to IMS. If operators can avoid vendors peddling monolithic and inflexible solutions, then IMS offers them the ability to migrate their networks at the pace most suitable for them, based on their own situation in terms of their existing network infrastructure and customer base.

Generating Revenues - It's About Access

For carriers and service providers the most important benefit of IMS is the capability it offers to rapidly create and deploy new multimedia services and applications which will be the revenue generators of the future. To access these revenue streams effectively operators need to make the new services and applications available to the widest possible range of users so they can deliver to all possible access points; IP phones, black phones, PDAs, softlines from PCs and laptops and wireless phones.

These multiple access points utilize a huge range of differing protocols and interfaces including legacy TDM, IP, VoIP, Wi-Fi, WiMAX, GSM, CDMA and WCDMA to name but a few. IMS is the technology that can bind these disparate technologies together from an application and control perspective, enabling the provision of services and applications to multiple wireless and wireline endpoints. This transparency enables operators to deliver revenue generating services to the widest possible audience. However, not every vendor has the capability to tie these different access technologies into the IMS core network. Some vendors will have expertise in legacy TDM but not in the wireless arena, and others will have the wireless skills but will be lacking expertise in IP. Furthermore, delivering a unified set of applications ubiquitously across multiple access networks is a rare art. To ensure operators have full access to the largest possible market for their new revenue generating services and applications they must select vendors whose skills cover the entire gamut of access technologies.

Supporting Legacy Services - Going Backā€¦ to the Future

IMS is all about delivering new services and applications such as presence, VoIP and mobile VoIP, instant voice messaging, mobile instant messaging (MIM), push-to-talk (PTT), video sharing, IP Centrex and click-to-dial from web pages. What is often overlooked is that both fixed and wireless operators already provide a huge range of legacy services based on Intelligent Networking (IN) such as toll free, translation and personal call lists. Many vendors pushing IMS at carriers tend to ignore the huge investment already made in these legacy services. In addition to the considerable investment involved, these legacy services also provide valuable ongoing revenue streams for operators and it is important that these are carried forward as the network evolves to IMS.

Enabling Services - Interaction Makes the World Go 'Round

The implementation of IMS offers operators the capability of creating and delivering new multimedia services and applications that will generate new revenue streams to offset the decline in voice revenues. As service creation with IMS will be quick and easy, many new applications will be brought to market.

As the number and range of services enabled by IMS grows, operators will have to address the issue of managing inter-service conflicts in real time at very fast rates. This functionality is a key element of the IMS core where it is handled by the Services Capabilities Interaction Manager (SCIM). The SCIM provides a central flowpoint so that, as operators add and subtract new applications and services, the transactions between the application server and the endpoint are managed correctly. The SCIM also allows the operator to mix and match services, including services from outside providers, modify the service flow and add or subtract value. The capability to deliver the SCIM functionality is currently limited to a few vendors as the majority of suppliers active in the IMS space do not have this expertise.

Keeping Track of Customers - One Database to Rule Them All

In the multiservice, multiple protocol/technology/bandwidth/ endpoint world of IMS, rapid access to customer data is essential. In today's networks services and applications reside in individual silos, each with its own customer database e.g. data on prepaid customers is in one database, and information on customers using instant messaging in another. The individual databases are not linked and there is no common database containing all the information about the customers. Replicating all the databases is too expensive, too difficult and too prone to error. With IMS it will be essential either to have, either a single large database or if this proves too difficult, the capability to tap seamlessly into multiple databases. Without this capability operators will not be able to access the user, deliver services to the user or charge for those services. In the IMS specification the central database is defined as the Home Subscriber System (HSS) although it is likely that some carriers will retain individual databases for different services with which the HSS is designed to work seamlessly.

Converging Networks - The New Frontier

An interesting, if somewhat unexpected, effect of the migration to IMS is that it is enabling the realization of fixed mobile convergence. Mature cellular markets are now saturated with penetration levels in excess of 100 per cent. Cellular operators are looking to IMS to drive up revenues through the provision of new applications and services but they are also eyeing a move into the wireline space. Technologies such as HSPA will enable cellular operators to deliver broadband connectivity anywhere anytime. With this weapon the operators are targeting traditional wireline customers with bundles of services and applications which are accessible in the office, in the home and on the road.

Wireline operators are responding by moving into the wireless space. Technologies such as WiMAX, which operates in unlicensed spectrum, offer fixed line carriers the ability to deploy regional or hotspot wireless networks which will generate additional revenues through the provision of broadband connectivity.

This ongoing fixed mobile convergence is being enabled by the migration to IMS.

Migrating To IMS - There is No Big Bang

The migration to IMS will be a step-by-step process rather than the Big Bang of an overnight transition to an all-IP infrastructure suggested by many IMS vendors. Certainly there will be some operators who are well-resourced and ambitious enough to deploy a completely new infrastructure. The majority of fixed and wireless operators will be more cautious, migrating individual parts of their networks to IP and IMS as the technology becomes proven. This approach will ensure that carriers will be able to support all their legacy devices and users throughout the migration process. By choosing the right suppliers they will be able to migrate each network layer independently and at their own speed.

If operators avoid monolithic and inflexible vendor solutions, IMS offers them the ability to migrate their networks at the pace most suitable for them, independent of the adoption of new devices. This approach enables operators to take advantage of the efficiencies of the migration to IP and IMS, based on their own situation in terms of their existing network infrastructure and customer base.

Amit Chawla is EVP, Global Business Units, Veraz Networks. For more information, visit the company online at

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