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By Cai Qingfeng

The multimedia telecommunications mode that integrates mobile, broadband and video is taking shape. It is an interesting question especially for mobile operators on whether to remain with a still dominant voice call network, or jump directly into an All-IP network.


All-IP: make or break?

Today even in the mobile world, voice is speeding up becoming and becoming a commodity. In fact, the ARPU of simple voice service is declining, while the expectation and requirement of users is increasingly becoming more farsighted in terms of the different types and multi-natured aspects of newer services, which will far outdistance simple voice service. The multimedia telecommunications era, in which voice, data, and video services will harmoniously coexist, is now dawning. So anyone choosing to stick with simple voice service, for all intents-and-purposes, is doomed to failure.

The IP network is able to bear voice, data, and video services, yet its "best-effort delivery" mechanism cannot totally ensure satisfactory QoS, which magnifies such problems as, delay, data loss, frame loss, and connectivity interruption, when operating under wireless circumstances. Even though it is possible for the IP network to bear non-real-time data services, it still has to face many serious challenges in the case of bearing real-time voice services. Thus, it is neither prudent, nor applicable, to assume that one can just simply replace a mobile network with an IP network.

Fortunately, operators are still compelled to maintain their current profit ratios, while at the same time, taking into account future development trends. Thus, they will at some point be forced to make a choice in regards to what course networks will continue to take in the future, the mobile softswitch - or IMS. In fact, more and more operators are realizing that a more sensible approach to constructing a future-oriented and efficient network, is not to place mobile softswitch and IMS in opposition to each other, but to work towards developing them in tandem.

Offering real-time voice services through mobile softswitch, and non-real-time multimedia services through IMS, is now the most common choice among operators. For example, Orange chose Huawei's mobile softswtich to construct its future 3G network in Belgium, and China Mobile stated that it will deploy softswitch to construct its 3G CS core network, while applying the IMS to its core network in order to enrich multimedia services. These choices were made based on a full analysis and positioning of softswitch and IMS, while also taking into account such aspects as investment refund and future development trends.


Mobile Softswitch + IMS

As is generally known, mobile softswitch separates the call control from the bearer. This not only simplifies the network topology, but also lends greater support to the IP network. Hence, mobile softswitch has a great advantage over the traditional mobile switch, which integrates the call control and bearer. In addition, key technologies such as, inter-office signaling BICC, H.248 protocol and interconnection test, have proven fully reliable. Currently, mobile softswitch is being put into commercial use on a large scale.

Based on the independency of access modes and the flexible mechanism of service triggering, IMS can easily realize various services via SIP/IP signaling, thus, making the integration of fixed and mobile networks, as well as telecommunication services and IT applications possible. Although service integration in the IMS is still in the process of being tested, it is viewed by many standardization organizations, including 3GPP and ITU-T, as being the development goal for NGN.

In the bearer network, both the mobile switch and IMS can be based on IP, and the service network can be shared. This means that the two have a foundation upon which to integrate. So, at present, all voice services are borne over mobile softswitch and some value-added services can be realized in IMS. In regards to the technology, network and services are gradually becoming more mature, and VoIP can be gradually introduced into IMS, to enrich voice and other value-added services, and to finally achieve an integrated network architecture and service provision based on IMS.

Admittedly, when considering how to best integrate mobile switch with IMS, operators must first consider their own strategy of evolution and marketing goal. They should likewise consider the services and the network when doing network planning, not only in accordance with their current status, but also in terms of future development and evolution within the industry. In short, their primary purpose should be to secure investment and to gain a sustainable and competitive advantage in the future.


Current Positioning

Phase 1: Tthe real-time voice service is carried over the mobile softswitch network and some value-added services are realized in IMS. Due to the better adaptation of voice services, the emphasis of network construction is placed on the mobile softswitch.


Network Evolution

Phase 2: Network evolution first takes place at the service layer and user data part. At this stage, real-time VoIP service is gradually enabled in the IMS domain, as the QoS of voice transmitted by the air interface improves and IMS terminals become more popular. Then, the two domains will overlap on a large scale and a consolidation of services and user data will occur. Finally, MSC will evolve into MGCF, and MGW into IM-MGW.

Phase 3: As IMS services becomes more popular, CS services and the network will begin to shrink in comparison. Yet for some users, only voice services will continue to be sufficient. It is recommended that all services from CS domain be rerouted to IMS, in order to be implemented. The SCP of IN will evolve into becoming the SCP-AS, by offering an ISC interface and MSC will evolve into the access gateway controller of mobile phones, in the CS domain. All inter-office ports used for signaling, routes and user data are based on the SIP, or Diameter protocol.


Conclusion

To co-ordinate the development of the mobile softswitch and IMS effectively avoids two misunderstandings: The first, being that some of us have formed an unrealistic picture that IMS is omnipotent. IMS is ready now to be used to provide end-to-end VoIP service on mobile network. Investment in softswitch is unnecessary. The other side of the picture is quite the opposite. IMS is useless, and thus, only mobile softswitch should only be used to offer all current services. IMS is also thought to be too complicated by many people, while real-time service is not applicable, so no need exists to develop it. Unfortunately, some vendors who are either able to provide a Softswitch only solution or an IMS only solution make the picture more turbulent.

The key to coordinating mobile softswitch and IMS is to clarify the present situation and to ensure the future evolution of networks. At this time, Huawei's mobile softswitch is taking a commanding lead in the world, while Huawei is also one of the leaders in world IMS market. In fact, Huawei now holds 5% of WCDMA's core patents (mainly R6 and IMS). In 2Q06, Huawei was selected to build the largest commercial IMS network in the world for T-Com and T-Mobile Hungary. To protect customers'investments and support their future developments, Huawei provides mobile softswitch which allows smooth evolution to IMS. Huawei can greatly help operators construct a future-oriented network, which will at the same time be able to fully satisfy current needs.