Call Continuity

One of the main areas of expertise for Cicero Networks is that of Voice Call Continuity (VCC). In 2006, Cicero first demonstrated calls handing over seamlessly between:

  • Wi-Fi and GSM
  • Wi-Fi and CDMA
  • Wi-Fi and WiMAX (IP to IP)

Since then, the range of scenarios has been extended to include handovers between:

  • Wi-Fi and 3G/LTE (IP to IP)
  • 3G/LTE and GSM
  • 3G/LTE and CDMA

As the availability of dual-mode handsets increased, the Cicero client was used to demonstrate VCC by all the leading infrastructure vendors. Using the same platform-independent Cicero engine, Cicero has now implemented VCC on Windows Mobile, Symbian and Android devices.

Cicero Solution for Call Continuity

The Cicero Networks solution for call continuity brings together all the elements of the Cicero product set:

  • CiceroSupra – the OTT variant of the Cicero client (IP-IP handover only)
  • CiceroInfra – the embedded variant of the Cicero client (IP-IP and IP-CS handover)
  • CiceroController – a SIP-based server to facilitate the handover between IP and CS
  • CiceroCMS - the Cicero client management server
  • Cicero Professional Services - the support and assistance required for successful deployment

CiceroInfra implements IP-CS VCC according to the 3GPP and 3GPP2 specifications, so it can be used alongside the VCC application servers of other vendors, if preferred. Similarly, the Cicero client applications can be managed using non-Cicero app management platforms.

Note that IP-to-IP handover does not require a specialist VCC application server. There are a number of ways in which the change in IP address can be handled and these can be discussed with Cicero during implementation.

Handover between IP and Circuit-switched Connections (CS)

The original requirement for call continuity covered calls that started on either Wi-Fi or GSM/CDMA and moved between these two networks as Wi-Fi coverage was gained and lost. This is a core capability of the Cicero solution and remains a key use case today. The nature of the IP network is not material to this use case, provided that it offers sufficient bandwidth to carry the audio traffic. Thus, the handover can just as easily be performed between an IP call on LTE and a 2G/3G circuit-switched call. Note that, while this is clearly a Voice over LTE solution, it differs from the single-radio approach being promoted by the cellular industry associations.

Note that handover can be achieved both ways between IP and CS without support from the mobile operator or access to the mobile switching centre (MSC). However, if handover is required for a call that starts on circuit-switched (MO or MT), settings changes within the MSC is required.

Handover between IP Domains

Handover between IP domains presents different challenges to handover between IP and circuit-switched connections. While the end-result is not always as seamless as IP-CS handover, there is less complexity involved.

In considering handover between IP domains, each of the scenarios should be evaluated for service inclusion:

  • handover between two access points on the same Wi-Fi network
  • handover between two access points on different Wi-Fi networks
  • handover between a Wi-Fi access point and a cellular IP network (3G or LTE)

There are network-side dependencies for achieving a smooth handover, particularly in the latter two scenarios, which can be discussed with Cicero in preparation for implementation.

Handover of Video Calls

While most cellular data networks are capable of handling a high-quality voice call, there are attributes of cellular connections that may cause them to be excluded for video calls. If a service provider is considering video calling as an element of its service mix, consideration should be given to removing the video element of a call as the user moves from Wi-Fi or LTE to the 3G domain. This can be implemented using the CiceroSupra client, though with slightly less granularity of decision-making on iPhone than on Android.

The area of voice call continuity is large and complex, even without considering the single-radio approaches to VCC being promoted by the cellular industry for VoLTE. However, most service providers underestimate what can be achieved, particularly in an environment where the cellular operator is not involved.

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