Service Continuity Solution for Multiple Scenarios

Service Continuity Need for Network Convergence

IMS support for Fixed and Mobile Convergence (FMC) helps operators explore market opportunities while removing the gap between wired and wireless networks. In fixed and mobile networks, FMC aims towards network convergence, equipment convergence, and service convergence, offering a seamless service experience to enterprises and individual users. With the increasingly expansion of WiFi networks and the introduction of dual-mode terminals capable of automatic handover between WiFi and cellular GSM/UMTS/CDMA networks, the key enabling technologies for FMC is to ensure service continuity between fixed and mobile networks.

The solution to IMS Voice Call Continuity (VCC) involves dual-mode terminals gaining access either through the Circuit Switched (CS) domain (GSM/UMTS/CDMA) or the IMS system. When choosing access through the IMS system, the dual-mode terminals can flexibly select the CS domain or IMS domain to establish call connection, achieving seamless bidirectional handover between different domains based on the relative policies. As a key application of the IMS-based FMC, VCC allows end users to enjoy a seamless service experience. With the access agnostic feature, IMS-based VCC enables different terminals (mobile, fixed telephones, and PCs) to implement seamless voice or multimedia service handover.

Service Continuity Need for Network Evolution

With the increase of real-time mobile services, such as video telephony and video conferencing, subscribers expect high-quality services through mobile terminals anytime and anywhere. Combining mobile and broadband wireless access technologies, LTE networks feature higher capacity, higher spectrum efficiency, and lower latency, thereby providing users with broadband mobile access and better service experience. However, due to coverage and investment protection in the initial stage of deployment, LTE networks will co-exist with 2G/3G networks and voice services will remain dominant in the network. Therefore, maintaining service continuity―especially voice call continuity when subscribers roam between the LTE and 2G/3G networks―has become a major issue.

Single Radio Voice Call Continuity (SRVCC) offers LTE/IMS-based voice service within the LTE coverage area, and CS-based voice service outside the LTE coverage area. When moving out of the LTE coverage area, a user’s voice must be passed smoothly from LTE to CS network, and network upgrade should be kept to a minimum. With SRVCC, an Enhanced MSC is employed alongside the MME in the LTE network, and a Session Continuity Control Application Server (SCC AS) in the IMS network is used for handover between CS and IMS. In this way, voice call continuity between the IMS and CS domains can be maintained without the need to upgrade all existing MSCs.

ZTE’s IMS-Based Integrated VCC Solution for Multiple Scenarios

As a leading global supplier of end-to-end IMS equipment, ZTE has been committed to developing an IMS-based integrated VCC solution for multiple scenarios (see Figure 1). It is a complete and open solution in line with 3GPP and 3GPP2 standards. Moreover, it enables dual-mode terminals to support two-way handover between a variety of IMS access modes, such as GSM/UMTS and WiFi, and CDMA and WiFi.

ZTE’s IMS-based integrated VCC solution implements the standard Dual Radio Voice Call Continuity (DR-VCC) procedure with the assistance of SCP. When some SCP functions are integrated into the VCC AS, deployment of the DR-VCC procedure can be simplified. With the help of Enhanced MSC, MME, and terminals, IMS-based integrated VCC supports SRVCC―which can initiate service handover from the LTE network to CS network.

As a key part of ZTE’s end-to-end IMS solution, IMS-based integrated VCC not only provides service continuity during the handoff among different IMS access modes, but also meets the need for VoIP functions in the initial stage of LTE deployment. For operators, it serves as an important means of offering diverse and differentiated services, and offering users a seamless and high quality experience.