zVOA: Empowering Converged Voice and Multimedia Services

With the rapid growth of smart phones and mobile broadband, mobile networks have entered an Internet era. Mobile operators are lowering their positions in the industrial chain while Internet operators are gradually moving to higher positions. Almost all mobile operators adopt a two-core (CS+IMS) architecture for their core networks. Mobile softswitch is used to provide voice, SMS, and USSD services for 2G/3G terminals, and IMS is used to deliver multimedia services to 3.5G, LTE, and WiFi broadband terminals. As defined in 3GPP standards, CS will evolve into an access network of IMS, and IMS will control both voice and multimedia services.

Internet operators such as Google and Tencent have advantages over mobile operators. They adopt all-IP access and a single point of configuration for universal reachability. With service pipes provided by telecom operators, they can deploy services faster and at lower cost. Moreover, Internet operators can control terminal and service software by themselves, independent of specific terminals. This ensures continuous and consistent service experience for users.

However, mobile operators have unique advantages in terms of phone number and network resources. They have MSISDN and IMSI number resources. A mobile subscriber identified by a unique MSISDN and IMSI number can have global roaming and communicate anywhere and at any time. Internet operators, however, have closed most networks that are incapable of interoperability. Mobile operators also have multiple access networks that support 2G, 3G, 4G, WiFi and LAN access modes.  Changes in user location and service capability can be perceived in real time. These help mobile operators deliver appropriate services to users. 

At present, mobile operators employ different control networks for different access modes. Mobile softswitch is deployed for basic voice and SMS over 2G and 3G networks, and IMS is deployed for multimedia services over HSPA+, EV-DO, LTE and PON broadband networks. This makes network convergence difficult and complicated. Although 3GPP has worked out IMS Centralized Services (ICS), which allows CS to access IMS, the cost of deploying this network is too high because of overly complicated architecture and an overextended control chain. 

There are two difficulties in running CS and IMS networks simultaneously:

(1)  CS service is a short to medium term cash cow for mobile operators, and this kind of revenue will decline in the long term. VoIP and Social Networking Service (SNS) networks will continue to absorb voice traffic, which worsens the competitive environment for CS.

(2)  Although IMS delivers multimedia services and opens up telecom network capabilities, evolving existing networks is difficult because of overly complicated architecture. IMS fails to beat SNS in creating new cashflow.

Because evolving mobile networks from 2G/3G to 4G is a long process, CS and IMS networks will coexist for a long time. A converged CS and IMS core is needed to reduce both CAPEX and OPEX. 

With ten years experience in mobile softswitch and IMS R&D, ZTE has put forward a Voice & Video over Any-Access (zVOA) solution for converging CS and IMS. In this solution, voice and multimedia networks are controlled in a unified way through one set of equipment. This provides services for both featured and smart terminals, as shown in Figure 1.

zVOA fully complies with standard interfaces for CS and IMS elements, satisfying user demands for multiaccess and service continuity. It employs state-of-the- art virtualization and cloud computing technologies for use on ZTE’s advanced ETCA hardware platform and TULIP software middleware. It also features intelligent Controller eXtensive (iCX) and integrative Media Gateway (iMG) products. iCX integrates standard mobile and fixed softswitches as well as IMS call control elements, while iMG incorporates media functions with integrated voice, video, and other content types. zVOA is designed for the migration of voice traffic from legacy phones to smart phones, greatly simplifying IMS deployment. IMS only needs two devices―iCX and iMG―to deliver voice and multimedia services as simply as CS.

ZTE’s ETCA is an enhanced platform based on ATCA standards. ATCA has a computing-centred architecture with weak switching and storage capabilities. To enhance switching, storage, and interface capabilities, ETCA inserts blades in the front and switches, storage, and interfaces in the back. Therefore, the ETCA platform implements both control and media functions of CS and IMS elements. 

ZTE’s TULIP is system platform software based on advanced middleware technology. Multiple TULIP-based network elements are integrated in one blade through the “platform + service” components. A unified platform process is responsible for the platform part that includes system resource management, system control, lower-layer signaling process, OAM, and data configuration and can be shared by all network elements. An independent service process is responsible for the service part of each network element. Communication between network elements is changed into IPC between service processes.  

iCX and iMG based on ETCA and TULIP can share hardware in both the softswitch and IMS domains. Hardware of the ETCA platform―including CPU, memory, and interfaces―forms a resource pool that can be shared by CS and IMS. Regardless of whether voice traffic occurs in the CS domain or will migrate to the IMS domain, system processing capability can be utilized. This helps minimize network adjustments and saves costs.

zVOA converges equipment and services of CS and IMS elements. It provides multiaccess modes such as 2G, 3G, 4G, WiFi, and PON. Whichever terminals are used and access modes are adopted, all system services are handled by iCX and iMG. This makes it easy to realize Converged One Number service and to enable user roaming between different access networks and terminals. 

iCX also provides a Service Centralization and Continuity (SCC) function, including Dual Radio Voice Call Continuity (DRVCC) and Single Radio Voice Call Continuity (SRVCC). When services are switched between different access networks or terminals, signaling procedures are greatly simplified, similar to handover between 2G and 3G networks. Moreover, iCX provides control functions such as MSCServer, Ehhanced MSC, CSCF, and VCC AS. iMG integrates MGW, IM-MGW, and MRFP media functions. iCX and iMG work together to implement Voice over LTE (VoLTE) and SRVCC. When voice calls are switched from IMS to CS, CS and IMS elements interact internally, and the signaling procedures seen from outside are similar to handover procedures between 2G and 3G systems.

zVOA will evolve to accommodate Social Networking Service (SNS) networks, providing abundant communication capabilities for terminals at different access networks. Mobile networks will be built into strong SNS networks that offer users a perfect communication experience. ZTE is poised to help operators enhance their competitive edge in the mobile Internet era.