ZTE´s Fixed-line 3G Solution, Road to FMC

Fixed-Mobile Convergence (FMC) is the trend of Next Generation Networks (NGN). With the development of network conversion, operators are focusing on the new fixed 3G solution to evolve the Public Switched Telephone Network (PSTN) into a fixed Softswitch network. Simultaneously a GSM or CDMA network can be transformed into a mobile Softswitch network as R4/LMSD (Legacy Mobile Station Domain). Therefore, the question of convergence between fixed and mobile networks will need to be solved.

1 FMC
How should FMC be implemented? So far the dominant considerations are network hierarchy and evolvement phases.

1.1 About Network Hierarchy
FMC can be implemented as follows:
    (1) Bearer Level
    Both the fixed network and the mobile network adopt the IP network as the bearer network, of which the application layer is independent. So far, all the fixed 3G and 3G R4 networks have also adopted the IP network as the core network.

    (2) Operation Level
    Operators can use the same operation and accounting system to manage their fixed and mobile network. The fixed network can employ the iHLR (Home Local Register) to connect with the HLR of the mobile network, so that the user data of the entire network can be managed in one unified platform.

    (3) Service Level
    In NGN the application server is separated from the control system. It´s an open and standardized system. It offers all kinds of multimedia services for fixed and mobile networks.

    (4) Equipment Level
    It is desired that fixed and mobile networks employ the same equipment to provide services. In fact, some main network elements such as the Softswitch system and multimedia gateway are designed in the same hardware platform and can be combined through the update of software.

1.2 About Evolvement Phases
    (1) Convergence Based on Circuit Switching (CS)
    It is difficult to converge a fixed network and a mobile network because the system architecture, entity partition and interface protocols are not completely the same.  Despite the networks having the same hierarchy architecture and the interconnection function of Signaling Gateways (SGs) being the same, difficulties still persist.

• Compared with the fixed NGN Softswitch, the functionalities in relation to mobile networks are added to the Mobile Switching Center (MSC) server in 3G R4 protocol such as management of the Radio Network Subsystem (RNS) and user mobility like roaming. The fixed Softswitch solution inherits all signaling and services of fixed local and transit switching centers. Besides, the Media Gateway Control Protocol (MGCP)/H.248 protocol is complemented to the solution. The mobile Softswitch solution inherits all service processing and signaling protocols of the Visit Mobile Switching Center and Gateway Mobile Switching Center (VMSC/GMSC), and the H.248 protocol is added with extended mobile functions.
• The coding mode of the bearer layer the mobile NGN adopts is much different from that adopted by the fixed NGN. Therefore, the interconnection between fixed and mobile networks needs to be transformed. The fixed Media Gateway (MG) needs to process the particular function like monitoring the user line, whereas the mobile MG processes the particular function as switching and interconnecting with RNS. Hence, the first phase of MG convergence is to assimilate the interface to support the same coding type as G.711.
• The mobile NGN uses end-to-end Virtual Private Network (VPN) access to guarantee QoS, in which the public IP address is used, so Network Address Translation (NAT) is unnecessary in the communication of network elements. However, the fixed NGN is much more complex because of different access modes like Local Area Network (LAN), Asymmetric Digital Subscriber Line (ADSL),  Wireless Local Area Network (WLAN), broadband wireless access and Hybrid Fiber Coax (HFC). Transit through different networks whether public or private is necessary in the fixed NGN. Therefore, network security becomes a big problem in the fixed network.
  

    In a word, the best solution of convergence in the narrowband phase is to implement integrated user data management and unified services.

    (2) FMC Based on IP Multimedia Subsystem (IMS)
    FMC based on IMS is much easier to realize because the control core of fixed and mobile NGN is an SIP controller in the multimedia broadband phase. Furthermore the architecture, signaling protocol, and service functionality are almost similar. In the long term, IMS offers mobile operators their best shot at the FMC market.
The IMS standard defines a generic architecture for offering Voice over IP (VoIP) and multimedia services. It is an international and recognized standard, first specified by the Third Generation Partnership Project (3GPP/3GPP2) and now being embraced by other standardization bodies including ETSI/TISPAN. The standard supports multiple access types including GSM, WCDMA, CDMA2000, wireline broadband access and WLAN. IMS takes the concept of layered architecture one step further by defining a horizontal architecture where service enables and common functions can be reused for multiple applications. The horizontal architecture in IMS also specifies interoperability and roaming, and provides bearer control, charging, and security.

    Currently the fixed NGN is in the R4 phase, mainly focusing on the emulational voice function of PSTN/ISDN and simple multimedia services. For the future, fixed NGN will develop into R5 or IMS phase to realize the multimedia functionality.

    ZTE´s fixed 3G Softswitch solution is coincident with IMS architecture, which proposes the horizontal architecture including service level, control level, bearer level and access level. The service provider is separated from the service controller. Both the fixed 3G solution and IMS provide a standardized interface for service development.

    Both ZTE´s fixed 3G solution and IMS adopt Softswitch to control and process the call. The difference between them is in Softswitch idiographic equipment and protocol. The core controllers in IMS architecture are Call Session Control Function (CSCF) and Multimedia Gateway Control Function (MGCF), which can provide direct access of multimedia terminals. However, the fixed NGN need a gateway in connection with MSC to access the mobile terminals. ZTE´s fixed 3G solution is advanced in supporting fixed access, which can interconnect with mobile terminals through a gateway. It can also evolve into IMS architecture smoothly.

    Both ZTE´s fixed 3G solution and IMS architecture are adopting a packet to transit the voice, signaling and data.
ZTE´s fixed 3G solution and IMS architecture are adopting the same gateway to interconnect with PSTN.
ZTE´s fixed 3G solution adopts Trunk Gateway (TG) and SG to connect with PSTN, whereas theIMS architecture adopts IM-MGW to connect.

    Compared to 3G IMS architecture, the contents of fixed Softswitch are
as follows:

• CS functionality: Softswitch, Integrated Access Device (IAD), Access Gateway (AG), TG, Multiple Service Access Gateway (MSAG) and SG
• PS functioanlity: Softswitch, data terminal and PC
• IMS functionality: SoftSwitch, SIP terminal, H.323 terminal and soft-phone
  All in all, the current fixed 3G solution focuses on the PSTN and simple multimedia services, In the future the fixed 3G solution will evolve into IMS architecture which focuses more on multimedia function.
  

2 ZTE´s Fixed-line 3G Solution
ZTE´s Fixed-line 3G Solution provides a service platform which integrates diversified networks and supports all kinds of services. Based on FMC, it helps PSTN, GSM, PHS, CDMA WLL and WLAN migrate to next generation networks. Moreover, the solution offers multimedia services with no restriction on the access methods.

2.1 Solution Overview
Figure 1 illustrates ZTE´s Fixed-line 3G Solution based on FMC.

    The access layer of the solution supports multiple accesses such as the access of PSTN, mobile networks (GSM, CDMA and 3G) and IP network. As for IMS services, the user equipment is required to have an IMS/SIP client for communicating with servers.

    The core layer comprises the routers and switches. It is a QoS-guaranteed IP network, providing the security and QoS.

    The control layer includes the Softswitch and IMS based on Session Initiation Protocol (SIP). IMS adds core capabilities, such as multimedia session control, QoS control and mobility management, to the IP network. The Fixed Proxy Call Session Control Function (FP-CSCF), which provides SIP user access for fixed intelligent terminals, is separated from Softswitch. Proxy Call Session Control Function (P-CSCF), a new Network Element (NE), will be added in IMS Phase 2. Then the mobile terminal can be supported by Softswitch. In addition, Softswitch supports CS of the mobile networks via MGCF.

    At the application layer, the application server implements value-added services for users, especially the IMS standard services (such as presence and group list management). Furthermore the integrated iHLR stores and manages users´ identifications which are exclusive in the entire network. It also supports the roaming function in order to realize mobility management. In addition, the management of all user data is centralized at iHLR. Therefore, all network management and billing systems can be unified on the same platform.

2.2 Fixed-line 3G Services
    (1) Interactive Services
    Most handset users have the experience of playing game in handset. It can´t compete with online gaming, in terms of the variety, vision effect and interaction. However, IMS can provide the online entertainment mode and multimedia communication mode for users. Hence the network game fans may play the online game with mobile terminals at any time and any place.

    Besides the network games, digital video, mobile TV, online music and interactive broadcasting will be popular services of the mobile networks in
the future.

    (2) Multimedia Services
    Multimedia services make it possible for people to share and transmit the data as voice, pictures, video and files. They make information communication more effective.

    Video sharing is a multimedia service. With it, users can watch live programs or video snippets while talking in the handset. Both parties of a conversation can watch the same program and discuss it.

    Push-to-talk over Cellular (PoC) service is a voice service based on cellular networks. It is called “the stunt of 3G era”. It seems to transplant the group function of MSN or QQ into the handset.

    (3) Message Services
    IMS creates the innovation space for traditional short message service. Voice, pictures, and video can be transmitted.

    (4) Network Merging Services
As IP technology is adopted across all kinds of networks, network architectures are converging so that wireless, wireline, voice, video and data network designs look essentially the same. As network architectures converge, IMS will become attractive to those who want to offer advanced services, from mobile phone operators to traditional phone companies and internet service providers.

2.3 Technical Features
    (1) The solution supports broadband packet networks such as IP network and ATM network.

    (2) Network construction is based on IMS and Softswitch architecture, and uses standard protocol interfaces to interconnect with different levels.

    (3) The solution supports narrow-band and broadband integrated access such as Plain Old Telephone Service (POTS), ADSL, LAN, Wireless Fidelity (Wi-Fi), Bluetooth and HFC.

    (4) It supports intelligent terminals like the home gateway, IAD, IP Phone, Video Phone and Soft Phone.

    (5) The user database is centralized and managed by iHLR.

    (6) It provides an open service platform based on Parlay/OSA architecture to implement
multimedia services.

    (7) A uniformed customer care and billing system is offered to implement billing, network management and customer care in one platform.

2.4 Solution Strengths
    (1) For Users´ Needs

• Richer Services and Easier Access
  The users can access information, entertainment and other content-rich services through one channel. Operators can extend their services to enable users to communicate in real time using any combination of voice, video, picture and messages.
• Convenience and Ease of Use
  With just one telephone number, whether fixed-line or mobile, a user can roam in fixed, mobile or IP networks seamlessly. Besides, just one bill makes payment convenient.
• Safe Communication
  The users can get reassurance in the QoS-guaranteed network when they
  are authorized to access their personal services.
  

    (2) For Carriers´ Needs

• Expanding Service Offerings and Revenues
  The packet-switched infrastructure enables the creation and delivery of new person-to-person multimedia services. It´s a way to protect operators´ business models and generate new revenues. With the new architecture, operators may also respond to new business opportunities quickly and flexibly.
• Reducing CAPEX and OPEX
  The Fixed-line 3G Solution provides interoperability between different networks and supports network convergence. Therefore, it helps operators reduce capital expenditures. Moreover, it integrates the billing, network management, and customer care functions into one system to reduce the operational expenditures of operators. It provides an open Parlay/OPI interface to make operators develop new services easily and with little cost.

2.5 Network Evolution
ZTE´s Fixed-line 3G Solution has an integrated design. All functionalities of IMS have been integrated into the Softswitch system of the solution. Although there is a gap in architecture standards and multimedia ability, the network architecture of the solution can evolve into the IMS architecture seamlessly. The main mission for evolution to IMS-based fixed-line networks is to standardize the module of Softswitch control functionality and complete the content of the network multimedia frame. The seamless evolution can be divided into three phases.

    (1) Phase 1
    The iHLR is employed to centralize and manage the user data of the entire network to transform the service spring mode of fixed-line NGN and complete the intelligence and mobility of the fixed network.SS7, including SIP I and BICC, plays an important role in call control processing. SIP is still in secondary status.

    (2) Phase 2
    The iHLR is evolved into a Home Subscriber Server (HSS), and the protocol interface is changed from MAP to Diameter/MAP.FP-CSCF which provides SIP-user access for fixed intelligent terminals is separated from Softswitch. The P－CSCF, is added in Phase 2. P－CSCF can provide the security association function between UE and P-CSCF. It also provides the SIP proxy function. Softswitch can support mobile terminals, as well as the CS field of the mobile network via MGCF.

    (3) Phase 3
    According to their demands, operators may add or combine the network elements or logic functionalities. For example, the Multimedia Resource Function Controller（MRFC）and Multimedia Resource Function Processor（MRFP）can be separate from the Emulation Call Control Function (ECCF).

3 Conclusions
Network evolution is a long term process. Undoubtedly, the IMS architecture is most promising in deploying and developing NGN. Using it, operators may adopt a strategy of first exploring IP multimedia opportunities.
ZTE´s Fixed-line 3G Solution proposes a way to evolve existing networks whether they are PSTN, GSM, CDMA or PHS to the unified NGN, in which voice, message, video and IP services can be integrated.

References
[1] IMS-IP Multimedia Subsystem[EB/OL]. www.3gpp.org/ftp/Information/WI_Sheet/NP-020572.pdf, 2005-03.
[2] Ericsson. IMS (IP Multimedia Subsystem)[EB/OL]. www.ericsson.com/products/hp/Ericsson_ IMS__IP_Multimedia_Subsystem__pa.shtml, 2005-09.

Manuscript received: 2005-09-12