Fixed Mobile Convergence Strategies

Ni Songtao

(China Information Technology Designing and Consulting Institute, Zhengzhou 450007, China）

Abstrac t:Fixed-Mobile Convergence(FMC)has become a hot topic in the telecom industry.Telecom operators are paying close attention to discovering a road of convergence based on their existing networks.However,there are no unified strategies regarding the implementation of FMC at present.This article analyzes the deployment of FMC strategies for different types of operators,as well as different network layers,while assessing the impact of FMC on the existing operating modes.The operators are suggested to take the existing network structure,operation and maintenance system and business modes into planning and find out their proper roads to network convergence.

T he concept of Fixed-Mobile Convergence(FMC)was proposed as early as in 1990s.However,due to the limit of technology and the lack of standards,it was not accepted widely,and relevant services did not become popular.

The traditional telecom architectures have been facing unprecedented challenges with the emergence of numerous new technologies and new services for recent years.Especially in 2006,the international standard organizations,telecom operators and equipment vendors strengthened the promotion of FMC.The final goal of the telecom industry is to establish a unified and converged communication information network.However,achieving this goal is a relatively long process,during which mutual penetration and convergence of different networks will always go with the network evolution［1-4］.

1 General Strategy of FMC

FMC covers many aspects such as the convergence of networks,services and operation support platforms.It won't be reached in one step.In addition,the operators might encounter the problems in backward compatibility and interoperability of technologies,service integration,customer relationship management,and more.Thus,achieving FMC will require a long time,and the solution to the convergence should follow a stepwise and layered strategy.

Operators might take the following steps to fulfill the smooth evolution from the present network to the future convergence architecture:

(1)Phase of Experiment and Validation

At the initialstage of the convergence,in order to validate the technological feasibility,service achievability,terminal applicability,and network bearing of the Internet Multimedia Subsystem(IMS),the operators will introduce experimental IMS-based networks into their own networks,with IMStests at a few points,which is required to be able to access the users in different networks,to implement multimedia services,and to achieve the interoperability with the existing networks and basic services.

(2)Phase of Market Cultivation

When the related standards and equipment become more mature,operators can deploy a few IMSin the hot-spot areas and major cities to offer the multimedia services to a small number of users,and implement its interoperability with the existing networks and basic services.

(3)Phase of Services Promotion The accomplished network deployment and the increasing users take the new services brought by the convergence into account.When the converged network is available,it will be used to offer diversified services.Chinese operators should cooperate with service providers,and develop all kinds of featured services.Besides services promotion,it is also very important to cultivate the terminal market.The interoperability between alltypes of networks in the converged architectures requires the good interoperability,stability,and diversity of mobile terminals.

(4)Phase of Integrating Operational Support Systems

The operators begin to adjust and optimize the converged networks at this phase.They implement the unified management of network resources and the user data associations by means of integrating the various support systems such as the user management,network management and billing platforms.

(5)Convergence Phase of Old and New Networks

IMSconstruction is expanded at this phase,and the access gateways of the traditional networks are introduced into the IMS.This puts the traditional networks under the control of the IMS,so as to fulfill the convergence of the old and new networks.Thus,the traditional voice networks,including the Global System for Mobile Communications(GSM)and Public Switched Telephone Network(PSTN),are no longer interoperated with the previous IMS,but are gradually marginalized and under the control of the IMScore network.

Moreover,the traditional Time Division Multiplexing(TDM)voice services will evolve to the Voice over Internet Protocol(VoIP)services,which accords with the development trend of the all-IPnetwork.

2 FMC Strategies for Different Types of Operators

Generally speaking,operators should consider the above steps when building the future convergence architecture.However,according to the characteristics of the Chinese telecommunication operation,the factors such as the license issue,the convergence of services,and the development of network technology must be taken into consideration in the process.Hence,Chinese fixed and mobile operators have different FMC evolution paths.

2.1 Suggestions for Chinese Fixed Network Operators

With the popularity of broadband access and the issue of licenses for the Third Generation of Mobile Communications(3G),FMC will greatly improve the competence of fixed network operators,and make them possess the sufficient share in the future telecommunication market.Therefore,it will play a significant role in the development of the fixed network operators,and the operators should actively take more efforts of pushing the development of FMC forward.

First,China Telecom and China Netcom,the two major fixed network operators in China,have presently established the large-scale Personal Handy-phone System(PHS),the well-known Little Smart wireless network.Its subscribers enjoy the similar services to those of other second generation mobile communication networks,except of roaming out of their home location.Therefore,it is feasible for the operators to first converge the PHSwith the fixed networks,the so-called Fixed-line and PHSConvergence(FPC),in the FMC process.For example,the service binding the fixed line and the PHS,QBOX(the Little Smart Wireless Services Solution),promoted by the two companies,is a product of this stage.

Second,fixed network operators may adjust and rebuild the network structure of their large-scale traditional PSTNs by making the fixed networks intelligent.In this way,the convergence at the service layer will be fulfilled,and new services can be introduced,while the traditional telecom services are retained.

The traditional switches can be replaced by Softswitches to implement intelligence of the telecommunication networks when a certain number of traditionalswitches in localnetworks drop out,or when new networks are built in the disadvantaged areas.Through the Softswitch intelligence reformation,the telecommunication network gradually possesses the features of the Softswitch network.It will then finish the smooth transition to a complete Softswitch network with the continual dropping-out of the traditional switches,and the addition and update of Softswitch equipment,so that it will achieve the goal of evolving to the Next Generation Network(NGN).

When the 3G licenses are issued,the FMC of fixed network operators will be accelerated.The operators should focus on the gradual convergence of the network service platforms and the operational support systems through which the operators can identically classify all the subscribers(including those in the fixed networks,the PHS,and the 3G mobile systems)according to the services they use instead of the networks they are in.By that way,the transformation from the access-based network to the service-based one can be fulfilled.

Last is the FMC stage of the core networks with the development and the commercialization of IMS.This stage is characterized with the unified core network and the services unrelated to the access modes.However,since the fixed network operators have established the Softswitch networks,and a part of the services are transferred from the traditionalfixed networks to the Softswitch networks,it is yet early to draw a clear map for the practical evolution from the fixed networks to IMS.Nevertheless,the requirements of 3G capacity expansion and the drop-out of some PSTN and PHSequipment all sway the introduction of IMSstrategically.

2.2 Suggestions for Chinese Mobile Network Operators

Chinese mobile networks are now in the Second Generation of Mobile Communications(2G).The deployment of IMScan help Chinese mobile network operators implement the application of multiple access modes and further enter the home broadband market.However,the current network construction experience and equipment development situation make it rarely possible for the operators to update the entire networks into Softswitch-based 3G mobile networks now.

The TMD-based 2G equipment has a large scale and a long life span.Therefore,the mobile networks should be evolved into the Softswitch networks step by step.

(1)Introducing Softswitch to Tandem Layer

Softswitch is introduced to the tandem layer to alleviate the burden of capacity expansion of the 2G TDM long-distance tandem network.The Tandem Mobile Softswitch Center Server(TMSC Server)is introduced to the controllayer for tandem of the Bearer Independent Call Control(BICC)signaling between big districts and between provinces.The IPflat bearer network is introduced to the media layer to carry the provincial long-distance traffic.

(2)Introducing Softswitch to Local Exchange Layer

When new 2G Mobile Switch Centers(MSC)are built to meet the demand of expanding the capacity of local exchanges,the Mobile Softswitch Center Server(MSC Server)or the Media Gateway(MGW)can be directly introduced to the local exchange layer.

(3)Building Softswitch-based 3G Network

If the mobile network operators get 3G licenses,they need to build the 3G network based on the Softswitch architecture,and integrate the 2G and 3G in one network for operation.

When the Softswitch-based 3G network is gradually established,mobile operators will also have to make the experimentaldeployment of IMSto validate its support for alltypes of access technologies and services.They acquire the operational experience of a full-service network by offering fixed data services to group subscribers in a small scale.

Then,the fixed and mobile core networks begin to converge,with the mature commercialization of the IMSand related technologies.This stage is characterized by the unified core network that is independent of any access modes.The current mobile operators are not experienced in building an entire fixed network.Therefore,the biggest benefit that the IMScan bring them is the capability to offer innovative broadband multimedia services.

In the future,both the fixed and the mobile operators will finally develop their networks into the unified NGN architecture.

3 Layered Implementation of FMC

Generally,both the fixed and mobile telecom networks are developing toward the layered structure that is getting clearer and clearer；the standardization and openness are the development direction of the protocol interfaces inside and between the layers.Therefore,according to the present layered network structure,the future FMC has the following overall implementations on the different layers:

(1)Converged core control,with unified IMS-based Softswitch

(2)Converged service application,that is,the unified application of fixed and mobile services

(3)Converged edge access,supporting multi-protocol-based access models for multiple services and multi-mode terminals

(4)Converged support system,having a unified network management and billing platform

3.1 Convergence on Core Control Layer

The traditional TDM-based telecommunication switched network is evolving into the architecture with Softswitch control.The future core control network should meet the requirements of unified access and control of the fixed and mobile networks.

IMSis independent of access,has unified session control and subscriber profiles,and offers an open and unified application platform.Therefore,IMShas gradually been recognized in the industry as the basis for FMC.

IMSis defined by the Third Generation Partnership Project(3GPP)Organization as the architecture for IP multimedia services.The International Telecommunication Union-Telecommunication Standardization Sector(ITU-T)and Telecoms and Internet Converged Services and Protocols for Advanced Networks(TISPAN)all introduce IMSinto the NGN architecture as the core network based on the Session Initiation Protocol(SIP)control,as well as for supporting both fixed and mobile access modes.

Therefore,IMS,a standard system commonly recognized by many organizations,willnot encounter the problem of protocols'compatibility among the different standard-giving bodies.This is the premise and the basis of IMSin support of FMC.

From the aspect of network architecture and protocols,the Serving-Call Session Control Function(S-CSCF)in the IMSarchitecture is the core of the whole network；the Proxy-Call Session Control Function(P-CSCF)is the access entrance for the IMSterminal；the Media Gateway Control Function(MGCF)and IPMultimedia Subsystem-Media Gateway(IMS-MGW)are the functional entities for the IMS's interconnection with the Circuit Switch(CS)and PSTN；the Multimedia Resource Function Control(MRFC)and Multimedia Resource Function Processor(MRFP)implement multiparty conferencing；and the Breakout Gateway Control Function(BGCF)is the demarcation point between the IMS domain and the external network.All these functional entities can be shared by both the fixed and mobile networks.In addition,SIPis the major protocolfor interfaces between the functional entities in the IMSarchitecture.SIPis an application-layer protocol,independent of the types of access networks.Therefore,with such a network architecture and protocol,IMSis able to support the FMC.

Therefore,the key step in the FMC process is to study and deploy the IMS-based core control network,which is an improvement on the operators'single and vertical network architecture.

3.2 Convergence on Service Layer

The ultimate goal of the FMC is to realize the convergence of fixed and mobile services.The converged services are the highlighted part of the future telecommunication business,and an important means for the full-service operators to fulfill their differentiated competition strategies.

The service convergence means that service applications are offered to subscribers of different access types through the unified service creation/transport platform,the independent core network(with call session control),and the independent access network.The applications based on the service integration include the sole number,Virtual Private Network(VPN),voice mail service,unified messaging,conferencing,and streaming media.

The standard and open interfaces play a crucial role in achieving the unified service platform,which makes it possible for the services to be created and deployed quickly and simply.The open and standard SIPand Parlay's Application Programming Interface(API)can implement the separation between the core network and service provisioning.They give birth to the service providers independent of the network operators,which helps make a positive open industrial value chain and push the business development forward.

3.3 Convergence on Access Layer

The access layer refers to the network layer that offer access to subscribers.FMC on the access layer mainly covers the convergence of Wireless Local Area Network(WLAN)/Bluetooth and GSM,and the convergence of WLAN and Wideband Code Division Multiple Access(WCDMA).

The standardization solution for the convergence of WLAN/Bluetooth and GSM,mapped out by the Unlicensed Mobile Access(UMA)organization,has been accepted by the 3GPP.In this solution,the WLAN/Bluetooth terminals access the core network of the GSM/General Packet Radio Service(GPRS)system through the IPaccess network.In this way,they can use the services offered by the GSM/GPRS network.

Moreover,in the convergence solution of WLANand WCDMAreleased by the 3GPP,the WLAN/WCDMA dual-mode terminal and the WLAN terminal can access the packet domain of the WCDMA network.With the authorization of the packet domain,the terminals can get the services offered by the 3G network.The services that the terminals in the WLAN can enjoy are the same as those used by the terminals in the WCDMA network.

Generally,the various access modes will coexist on the access layer for a long time to meet the subscribers'different demands.The convergence on the access layer aims to make the fixed and mobile access modes complementary and bring into play their respective advantages,to provide fixed and mobile subscribers with high-quality but low-price services and“ubiquitous”service experience.

3.4 Convergence of Terminals

Terminals'convergence plays a very important role in the process of FMC.As the important part of the network convergence and the last link of the industrial chain of the network convergence,the terminal offers to users the most direct experience of services.Without the terminal convergence,it will be very hard to fulfill the final network convergence.

With the gradual industrialization and marketing of the intelligent terminals,the intelligent Personal Digital Assistant(PDA),Wireless Fidelity(WiFi)/GSM dual-mode and Bluetooth/GSM dual-mode terminals are replacing the Bluetooth mobile phone,Bluetooth gateway and WiFiterminals that are capable of offering wireless access at a certain range.The multi-mode intelligent terminals permit the subscribers to choose proper networks(fixed or mobile)on their own will.In addition,the network itself can intelligently make the best action corresponding to any access modes.

The solution to the terminal convergence is closely related with that of the service convergence.The service capabilities of the converged terminal are not only tightly connected to the specific solutions,but also need operators'participation in service customization.This is one of the difficulties in implementing the convergence of terminals.Other technical difficulties include the dual-mode handover of voice and data services and service security.

3.5 Convergence of Operational Support System

The convergence of operational support system may involve the operators'management system.Nevertheless,the possibly direct way is the convergence of the billing system,which is urged by the requirements of the unified charging,unified bills and flexible charging strategies.

The convergence of the billing system include the acquisition convergence,billing convergence(both online and offline),accounts convergence,and charge convergence.Among the four convergence levels,the charge convergence is the weakest.It can only integrate all the service expenses of a user into one bill.However,it cannot support crossed discounts of different services,and the integration of pre-payment and post-payment.The account convergence is stronger,but it can only fulfill the binding and crossed discounts of different post-payment services based on the levels of accounts,with no support for pre-payment services.The billing convergence can not only fulfill the multi-service binding and crossed discounts based on the levels of detailed bills,but also support pre-payment services and real-time service integration.The acquisition convergence can fulfill the convergence of multiple services,as well as that of pre-payment and post-payment services,on a unified platform,support crossed discounts of different services,and offer various payment options to the subscribers.It is the ultimate goalof the convergence of the billing system.

In general,the convergence of operational support system brings great convenience and many benefits to subscribers.Therefore,it helps enhance the subscribers'loyalty.It is regarded as an important strength of full-service operators,and is also the preferential service offered by them.

4 Influence of FMC on Network Operation

4.1 Converged Architecture Reduces Operational Cost

The future converged network based on the IMScore control architecture will give operators opportunities,and will also reduce the related operational cost.If the operators would want to offer comprehensive services before the fulfillment of the FMC,they would have to build multiple single-service networks.This kind of vertical structure of one network to one service will cause complex network management,as well as high Capital Expenditure(CAPEX)and Operational Expenditure(OPEX).However,the operators have to reduce the CAPEX/OPEXunder the pressure of competition.

On the basis of the separation between the Softswitch control and the bearer,IMSfurther separates the control layer from the service layer.Therefore,IMSnot only takes the cost-advantage brought by the Softswitch bearer integration,but also uses its horizontal system architecture to lower the cost of service creation.Moreover,it centralizes the user data management,billing and other network capabilities,which creates the condition for decreasing the cost of network operation and maintenance.

The IMS-based FMC services allow a flexible selection of networks and terminals.Therefore,they can meet the operational demands of operators.It will also help the operators(including mobile,fixed and full-service network operators)gain better competence in the long-term development,and put them in an advantageous position when the new services asks for the mode transformation.

4.2 Fast Service Deployment Brings Opportunities to Operators

Essentially,service is the main driving force of the FMC development.In the times of voice telephone,there is no basic difference among the services offered by different operators.Either the traditional telephone services,or the VoIP,can just meet the people's primary demand for speech communication.The operators,in a more and more fierce homogeneity competition,usually make price wars to stabilize their customer groups.However,the price wars lead to a persistent decrease in charges for voice services,and accordingly in the Average Revenue Per User(ARPU).Therefore,the operators are eager to create new growth points of earnings through service innovations.At the same time,with the development of the mobile and data communications,people are not satisfied with the simple voice services,but are eager for diversified communication means and personalized experience of multimedia communications.The capability of offering multimedia services will decide the operators'future earning power,and their competence in the telecommunication market.

The converged network,based on the IMScore control,supports differentiated services through the unified control.It especially offers the services open to both the fixed and wireless subscribers,and ensures the identity of the subscribers'experience of services through the unified core control layer.Although some IMS-based services are not perfect,the architecture of IMS depicts a future network that will support all the services,and it has gotten the attention of many operators,who expect to provide their customers with differentiated and diversified services through the establishment of IMS.

4.3 Continual Exploration Needed in Operational Modes of Converged Network

The future IMS-based converged network obviously has the same characteristics on both technology and service as the Internet.Technologically,the complete separation between the control layer and the service layer simplifies the network,and it is only required to provide the necessary trigger and routing functions(with more intelligent SIPterminals).Moreover,the service layer permits the third party to offer services through the open interface of the Open Service Architecture(OSA).The IMS-based services like video conferencing,group management,Push-to-Talk-over-Cellular(PoC),presence services,video-telephony,Instant Messaging(IM),VoIP,interactive gaming,video sharing and file sharing can find the same or the similar services on the Internet.However,compared with the Internet services,the IMS-based services focus on the subscribers'mobility more.The commercialand profiting models of the Internet are not the successful solutions to the telecommunication networks.Therefore,operating the IMSnetwork is a challenge to the telecommunication operators,although the IMScan flexibly and quickly offer abundant services.

First,the traditional operators'advantage is their big network and large customer group.Their disadvantage is the lack of experience in the information and content services.Besides,the subscribers have been used to the free Internet services.Most of the IMS services are much more like those of the Internet.Therefore,pressing questions on how to develop the services based on IMS,how to develop those attractive services,how to make the customers accustomed to use the services,and how to charge on the services,willarise in the practical operation.

Second,the telecommunication operators should strengthen their control on the IMScore network.The traditional Internet is not a network qualified for the operation and the management.It is totally open.The telecommunication operators could only charge the channels used by traffic or by the time length,and make a limited control on the information service carried through the channels on the Internet.There will also be the end-to-end IPconnection between users in the future IMS-based network,which will require more on network maintenance and operation,such as on the subscribers'management and stream-based billing.Although the 3GPPhas defined the security,Quality of Service(QoS)and billing in the related standards of IMS,the further research and improvement is necessary.

5 Conclusions

In overview of the development of the globaltelecommunication industry,FMC is the future trend,and it will totally change the present environment of the telecommunication competition.The introduction of the full-service operation mode will especially bring great impact on the present network architecture and the operational systems［5-6］.In face of the opportunity and challenge brought by the FMC,the telecommunication operators should not only actively trace and research the related technologicalstandards,but also analyze and map out their network structure,operation and maintenance system,and operationalmodes of services,so as to find their own proper ways towards FMC.