Saturday, March 28, 2009

Defining an IMS Strategy

As a set of specifications or as a set of products provided by telecom suppliers, IMS is not the answer about how to ensure a bright future for telecom operators.

Basically, IMS should be perceived as a toolkit, which can be used alternatively or successively in various manners leading to drastically different results. As a consequence, an operator needs to define a short, mid and long term strategy based on IMS that suits its business strategy, and it has to take the adequate measures to apply this strategy. Here, we are touching the biggest IMS issue. It is not technical but rather cultural, practical and organisational.

In this post, I will try to outline some potential elements of an IMS strategy.

Deploying IMS

While some operators may simply decide to deploy IMS as part of their network evolution roadmap, many require an initial motivation to take the decision to go for it.

At the time being, the main triggers for deciding to deploy an IMS network are certainly the following:
- Replacement of the legacy circuit-switched network for fixed telephony services (IMS used as PSTN emulation subsystem).
- Deployment of a carrier grade VoIP solution for fixed residential customers, possibly with mobile/fixed convergence services including or not call contuinity between fixed and cellular access (knowned as voice call continuity).
- Deployment of carrier grade enterprise services including for instance business trunking, IP centrex or fixed mobile convergence.
- Deployment of a compelling set of mobile services through the Rich Communication Suite (RCS) or something else.
- Deployment or migration of an IPTV solution making use of IMS.
- Deployment of a selected set of IMS-enabled fixed mobile services.

However, such initial motivations are not always strong enough to validate investments in IMS.

For instance, a fixed operator may wonder why it should invest in IMS to reimplement a telephony service whose revenues are rapidly decreasing and which is likely to eventually be offered for free. Likewise, the usage of IMS for a specific service like IPTV or RCS or for a specific business segment like enterprise may not be economically worth for the operator.

It is therefore necessary for the operator to have a strategy for extending the usage of IMS beyond its initial deployment scope in order to have an optimal return on investment. Such a strategy is also fundamental for the operator to decide on future investments.

More especially, any decision to eventually replace a pre-IMS service implementation (e.g. telephony, messaging, IPTV) with an IMS one may impact the investment and evolution plan for the pre-IMS implementation.

The Future of Telephony

The future of existing telephony services and their implementation is a tricky issue that needs to be addressed carefully.

Basically, IMS permits to:
- Re-implement classical telephony services for legacy terminals and narrowband access (IMS as a PSTN emulation subsystem in ETSI TISPAN)
- Implement a new generation of voice-centric telephony services for new terminals (e.g. SIP phones) and broadband access
- Implement a new multimedia communication experience, in which voice is only a media component among others, whether they are related to person to person communication (e.g. messaging, video), content (e.g. streaming video, files) or data (e.g. events, application sharing, shared browsing).

The operator needs to clearly identify these services, decide which ones it wants to deploy, how, and in which timeframe.

Once this diversity has been understood and associated decisions have been taken, the operator can start to think about the implementation of related value-added services. For instance, are or should the value added services be the same or be different for each variant? Should they be implemented on the same or different platforms?

The operator can also think, if relevant with its plans, about how these different types of voice-related services should co-exist and possibly interwork.

The relationship between IMS and classical telephony services is of particular interest. It goes beyond the question of replacing the circuit-switched core network with an IMS based IP network as the two networks will co-exist for some time, and during this transition phase the support of value-added telephony services for both may be a question in itself.

The operator may have the choice between several alternatives and decide to opt for one or to evolve from one to the other over time:
- Using different service implementations in both networks (e.g. Intelligent Network in CS and a Telephony Application Server (TAS) in IMS)
- Reusing legacy Intelligent Network solution(s) in IMS
- Re-implementing services on a new platform able to support both IN and IMS ISC interfaces
- Reusing the IMS TAS for delivering value-added services to circuit-switched voice, in replacement to Intelligent Network servers (ongoing standardisation in 3GPP as IMS Centralized Services)

The future of messaging

In mobile networks, various messaging services can exist such as SMS, MMS and IMPS (OMA standard for mobile Instant Messaging).

IMS messaging has the potential to emulate all these messaging services and to add more to the user experience. The operator may therefore have to decide if and when it wants to eventually replace all of the existing messaging services and how it wants to manage the transition phase during which IMS messaging takes off and co-exists with them.

Moreover, as for voice, the multimedia nature of IMS makes that messaging may eventually cease to exist as a standalone service and be part as a multimedia component, of a more global and powerful multimedia communication paradigm. Should the operator skip the silo IMS messaging step and go directly to the multimedia communication service or should it implement one after the other? If so, how should the migration be performed?

IMS as a multi-service platform

An important feature of the IMS service architecture is its ability to support the harmonious co-existence of multiple services related to communication, content and data. This is a discriminating feature compared to a non-IMS SIP network, which lacks a standard service architecture and requires ad-hoc and often cumbersome support for the co-existence of several services, with limited multivendorship possibilities, and this until the architecture explodes after the hack too much (as this happens with all silo architectures whose limits are pushed too much).

An advantage of using an IMS core network as a multi-service platform is its ability to factorize and make coherent such functions as service discovery, user identification, user authentication, QoS and policy control, security, detection of the access technology used by the subscriber for service adaptation purpose (e.g. UMTS vs. LTE, xDSL vs FTTH) or interworking among operators, among others.

There are important cost savings to be achieved through deploying multiple services on IMS, both in terms of simplifying service implementation and harmonizing the support of functions common to multiple services.

There can also be important benefits related to the centralized knowledged in the IMS of service usage by subscribers, like the ability to apply QoS policies that take into account the multiple services used in parallel from the same home or device.

The operator needs to prepare and plan for the gradual support of new services and the porting of existing ones on IMS. This implies, among other things, not to take architectural decisions related to IMS that are specific to one service and may prevent the deployment of new ones in the future. To take a simplistic example, an Initial Filter Criteria routing all SIP INVITEs to a TAS may work as long IMS is used to support a single telephony service. On the other hand, it can be a source of nightmare as soon as an IPTV or IMS Messaging service (both making use of INVITEs as well) is introduced.
Using IMS as a multi-service platform is not always straightforward for operators which are used to deploy silo services and whose decision processes and organizations are defined according to this paradigm. An IMS strategy may therefore include organizational and decision process changes as well.

IMS for new services

I have often read that IMS cannot support new services. This is a wrong assessment.

The versatile nature of the SIP protocol, illustrated by the invaluable concept of event packages, the ability to integrate the IMS application layer in a more global SOA (Service Oriented Architecture) and UOA (User Oriented Architecture) framework, and the possibility to strongly integrate IMS with the Internet and its services create thousands of opportunities for new services, many of which are not connected to person to person communication.

The operator needs to define a strategy related to this opportunity for innovation: whether it wants to use this opportunity, how, what changes need to be done in organizations, skills and practices.

IMS for a new user experience

Possibly more important than new services, IMS permits to create a brand new user experience which makes that the frontier between services as we know them can totally disappear.

As already mentioned above, multimedia sessions permit to deliver communication, content and data services in a combined context.

Moreover, IMS-based fixed mobile convergence has the potential of eventually making the device and access technology used by the subscriber a mere detail of service delivery. Using a converged subscription, a user could access all its services from all its device, from all access technologies (whether fixed or mobile) and with the same identity.

Such a full convergence cannot happen overnight due to various reasons related to organizations, existing business processes, cultures, regulation, and to a much lesser extent, technical issues.

The operator must therefore plan and prepare for these evolutions, defining clear steps towards a the target. For instance, the operator may initially decide to use the cost savings aspect of IMS based fixed mobile convergence, by sharing the same IMS core network between fixed and mobile subscriptions. It also must decide if and how it eventually wants to support full convergence. For instance, will the operator eventually offer only converged subscriptions or will it permit subscribers to chose between converged and non-converged subscriptions? In this latter case, what would be the implications?

Managing the complexity of the IMS application layer

This blog has often tried to describe the fantastic power of the SIP protocol and the IMS service architecture to deliver rich services.

One of the outstanding features of the service architecture is its ability to combine services or service logic components residing in the devices, in the operator's network and across different operators' networks, the Internet or Enterprise networks, in a very flexible manner.

There are basically two composition mechanisms:
- Implicit composition: device and network based service logic or services are chained in the SIP signalling path.
- Explicit composition: device and network based service logic or services make use of each other through an appropriate interface like SIP, web services, HTTP, RTSP, H.248 or another protocol.

While very powerful from a functional perspective, this potential leads to new complexity related to distribution, compared to the traditionally centralized implementation of telecommunications services.

The operator must therefore find ways to deal with this complexity by addressing issues like the definition of relevant compositio handling functions like the SCIM, the management of service composition data like Initial Filter Criterias and SCIM information, the addressing of potentially redundant or conflicting functions across different servers, or the determination of approaches to measure quality of experience or determine root causes for potential problems.

Optimizing the IMS application layer

These distribution and composition mechanisms also lead to potentially critical optimization issues.

These optimization issues may for instance relate to:
- End-to-end performance if too many physical servers are involved in service delivery. In an extreme case, a spectacular service on paper may simply be irrealistic in practice due to disqualifying delays in service delivery to the end user.
- The load of IMS entities, more especially the S-CSCF and application servers, which are essential components in service delivery and composition.
- The cost of deploying and operating services if the application layer is too heterogeneous and too distributed or if features are duplicated across multiple servers.
- The impact of the failure of a server, for instance an application server, on subscribers. For instance, how many users will be impacted by the failure of an AS and for which services?

The operator must therefore define an optimal strategy to deploy services, which optimizes the user experience while minimizing costs and risks. This issue has to deal with service platforms and service topology. For instance, IMS offers alternatives to the dedication of an application server to a certain service for a large portion of subscribers by permitting on the contrary an application server to support a variety of interdependent services for a smaller subset of subscribers.

Service Platforms

The choice of service platforms is a key component of an IMS strategy, though only one component among others.

An operator has basically the choice between two alternatives for a service platform:
- A black box delivered by a service supplier.
- An open service platform delivered by an IT vendor, usually called Service Development Platforms (SDPs) in a telecom context, on which services are applications delivered by application providers or implemented in-house by the operator.

Concerning SDPs, the operator has further choices between alternatives like IT-centric platforms (e.g. J2EE, .Net) or telecom centric ones (e.g. JAIN SLEE, OSA application servers).

Each approach has its advantages and drawbacks, and these may differ depending on the considered timeframe. The operator should therefore define criteria permitting to select the most appropriate platform for a given service in the short, mid and long term, and prepare for the potential migration from one to the other, when appropriate.

IMS clients and devices

The best package of IMS services is useless if it is not adequately supported by clients and devices.

The operator must address such key issues like:
- The distribution of service logic between devices and the network. Note that depending on the characteristics of a device (e.g. high end vs low end, mobile vs. fixed), a given service may require different implementations or implementation variants for access by different devices.
- The distribution of service logic and IMS support between different devices on the customer premises, e.g. a home gateway and end-devices.
- The management of IMS client updates to support new IMS services.
- Optimizing device management by using IMS-intrinsic benefits.
- Spreading IMS support in the wider range of devices.
- Presenting IMS services in an optimal way to end-users in order to make them attractive and make their access and usage intuitive.


IMS by itself is not an answer to the challenges an operator will face in the future. An operator should define a coherent strategy comprising which components of the IMS potential it wants to use, in which timeframe and how.

While many operators have already deployed IMS or are planning to do so, usually with a well defined short term objective, I have the feeling that only a few are actively working on a mid and long term IMS strategy.

This is a pity, because defining such a strategy would permit to:
- Help IMS acceptance in the company by outlining the short, mid and long term benefits expected from it.
- Anticipate on changes required in organizations, practices, and skills to apply the strategy. By doing so, speed up the implementation of the strategy.
- Have a better control of short and mid term investments, for instance by avoiding excessive investments in implementations or services whose lifetime will be shortened by the implementation of the IMS strategy.

As you may infer from this post, I have put a lot of thoughts in these topics. Do not hesitate to contact me on this.



Franz Edler said...

Hi Christophe,

I highly appreciate your thoughts on the importance of an IMS strategy. This brain-food is very important today where sometimes I already have heard phrases like "IMS is dead" because of its complexity.
I also do not see any other chance for operators to enable innovation and to create value in the future without IMS. But this - as you explain perfectly - requires a strategy and a commitment which is often not available at operators.

Thanks for your thoughts.

Anonymous said...


Rohit Joshi said...

Thx for your insights on IMS. It seems operators don't have option going forward without IMS if they want offer converged services by reusing the infrastructure and reducing the cost.
Keep up the good work!!

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Rahul said...

Hi Christophe,
That is very nice blog for digging in IMS.
Iwant to ask a question, that How Multidevice in IMS is deal. It means that if a user has Same public ID and multiple Instance then how IMS manage whole senario? How Invite, File transfer, and other services will be used?

Rahul said...

Hi Cristophe,
Can you explain the Group Chat in IMS, and How it works.

Thanx in Advance. :)

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