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Verizon Wireless' A-IMS initiative: focus on service continuity
Jean-Charles Doineau, Roger Entner and XJ Wang

http://www.ovum.com/go/content/c,65714

On 27 July 2006, along with its vendor ecosystem partners Cisco, Lucent, Motorola, Nortel and Qualcomm, Verizon Wireless made an announcement about its IMS initiative, called Advances to IP Multimedia Subsystem (A-IMS). This initiative is emblematic of the current development of the IMS infrastructure business: pick up the good in IMS, and expand in areas not standardised.

Verizon Wireless' deployment of CDMA2000 1XEV-DO Revision 0 in October 2003 has kick-started 3G deployments in the US market, putting pressure on Cingular and Sprint Nextel to follow suit. Unlike its EV-DO announcement, Verizon Wireless is not the first tier 1 mobile operator in the US market to embrace IMS architecture: Sprint Nextel and Cingular made their announcements before Verizon Wireless. However, Verizon Wireless' approach clearly has more of a carriers' view on how the industry should implement the IMS architecture. A-IMS places emphasis not only on SIP-based applications but also on non-SIP-based applications.

Supporting non-SIP-based applications is really the key to ensuring service continuity during the core network evolution. This has not been the focus of IMS specifications so far, which assume in Release 4 that a VoIP move has already happened in the core before moving to IMS in Release 5. As a consequence, the standards consider there to be a de facto approach to service execution, which is agnostically based on SIP, and have often neglected to take into consideration other sorts of traffic, whether IP-based or not.

Verizon Wireless and its partners have been working on such issues for the past twelve months. One of the main areas in which they have been working is end-to-end mobile VoIP. This aims to provide truly mobile, high-quality voice services that an operator can deploy as a viable replacement for existing cellular voice services, from access to core. A-IMS focuses on optimising voice latencies, whilst at the same time providing the operator with the ability to manage and control the voice traffic using an IMS-compliant service control plane.

A-IMS also focuses on providing end-to-end security features and management of services for business customers, as well as expanding some fixed services into the mobile market, such as IPTV.

This work complements the work done in 3GPP and 3GPP2. Both standardisation bodies more or less assume, at least before Release 7, that service providers will operate multimedia combinational services using SIP. These services, combining voice and data in realtime communication flows, can really be seen as the future of telephony. However, surprisingly enough, preparing this move to the future of telephony via the introduction of non-SIP VoIP in the access network has not been considered - leaving open a gap that Verizon Wireless fills with it's A-IMS framework.

According to Verizon Wireless, the A-IMS task force is in the process of submitting suggestions to not only 3GPP2 but also 3GPP and TISPAN. These suggestions could lead service providers considering IMS to follow different paths for the introduction of IMS services:

the value-added services path: leaving voice services operation in the TDM plane, and building SIP combinational value-added services at the same time. Gradually pushing end users into using more SIP-based combinational value-added services instead of voice
the voice migration path: move to VoIP first and develop through telephony over IP (ToIP) an attractive end-user experience that will encourage usage of combinational services over time.
Figure 1 illustrates Verizon Wireless' view on SIP and non-SIP based services that will be supported by A-IMS.

Figure 1 Examples of services that will be supported by A-IMS



Source: Verizon Wireless

Regardless of how this will play out in the next couple of years, by supporting both SIP and non-SIP applications, A-IMS focuses on seamless service migration during the evolution of the core network architecture. It represents a very good example of what could be expected from carriers wishing to move to VoIP using an IMS-compliant evolutionary path.

Jean-Charles Doineau leads Ovum's Service Infrastructure research practice, which focuses on the applications market that enables service provisioning in the telecoms space.

Roger Entner is the VP Wireless Telecoms for Ovum, covering market developments, technology trends and companies in the North American market place.

XJ Wang is a Research Director with Ovum. He focuses on application and service platforms, wireless infrastructure, new business models of telecoms equipment manufacturers, and telecoms market strategy and trends in the greater China area.