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Mobile & Wireless
A Call to Arms
Industry Titans Map Out Enhanced IMS Architecture
by Sean Buckley
While choice in life is good, it can sometimes lead to complexity. This was the feeling Ed Salas, VP of Network Planning, Verizon Wireless, and his technical team had when they started to examine their IMS (IP Multimedia Subsystem) plans.
“Over the course of a year, we were driving questions about implementation, and asked ourselves if all of the issues with an IMS architecture were resolved or not,” explained Salas. “The net-net of that discussion with my team was that we emerged with a whole lot more questions than answers around IMS. Not that anything was necessarily bad about IMS. It was, in fact, great, but we saw a significant amount of complexity given the number of 50-plus functions and growing and 30-plus interfaces specified and growing. Also, we saw other areas that were not addressed, such as end-to-end security, the ability to manage the customer experience, and specifically the need to manage not only SIP-based services, but also non SIP-based services.”
With these issues in hand, Verizon Wireless went to its key suppliers—a list that includes Cisco, Lucent, Motorola, Nortel, and Qualcomm--to develop a task force that would work to resolve some of the real-world issues it saw with the current IMS architecture. This work culminated in the A-IMS (Advances to IMS) architecture.
Initially based on CDMA EVDO technology, A-IMS will complement the existing 3GPP/3GPP2 standards work with enhanced management, security, and the ability to support SIP and non-SIP-based applications. Building on the existing IMS standard, A-IMS will enable operators to support a wider suite of applications and offer those applications to a broader base of businesses and consumers, while at the same time providing better management and security of those applications than the initial standard calls for.
However, A-IMS is not just about Verizon Wireless or CDMA. As an access-agnostic infrastructure, A-IMS will be applicable to any wireless or wireline carrier deploying IMS.
“Our intent here is to move into the standards environment—not only 3GPP2, but the 3GPP community, IETF and other wireline standard groups—because we think the issues we are addressing are agnostic to the access technology,” said Salas. “We are addressing the common issues that all carriers who want to manage IP services have to face.”
Bridging the Gap
Certainly the benefits of SIP are well documented; however, the fact is that many of today’s wireless services are non-SIP-based. This will pose a major limitation for operators that want to deliver non-SIP based applications; they would have to seek out proprietary methods.To remedy this problem, the A-IMS architecture has built in a number of the necessary hooks to control both kinds of services such as accounting, authorization, authentication, policy control, service control, application interaction, roaming/peering, QoS management, and security.In order uniformly manage both SIP and non-SIP services, A-IMS introduces two new elements: a Service Broker to manage the invocation of services and a Policy Manager, which allows the service provider to manage the usage of network resources on behalf of both types of applications.
One of the most obvious services that will be a focus in the A-IMS architecture is end-to-end mobile VoIP as a replacement to existing cellular voice service. A-IMS has built in hooks to ensure quality mobile VoIP service by optimizing voice latency, while giving the wireless operator the ability to manage and control voice traffic.
Ovum Research, for one, believes that operators could take two approaches to delivering IMS services:
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value-added services path (leaves voice services in the TDM plane, while building value-add SIP services);
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voice migration path (move to VoIP and then develop attractive end-user service that will spur combinational services over time).
Still, Ovum Research says that overall support for SIP and non-SIP services will be the main priority. "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,” said Ovum Research in a statement. “It represents a very good example of what could be expected from carriers wishing to move to VoIP using an IMS-compliant evolutionary path."
Maintaining Order
No matter the technology deployed, for the customer it’s all about having a good experience. Along with the support for multiple SIP and non SIP-based services, the A-IMS architecture provides a more robust set of management and security features that were not present in the initial IMS standard.
What makes the A-IMS security element unique is its layered approach, with all network elements protected from attacks and being able to manage any attack. A-IMS resolves the issues of end-to-end security and management of the customer experience by outlining methods of intrusion detection, which will identify Denial of Service attacks and service breaches from both inside and outside the carrier network. Having end-to-end security will be key to helping service providers manage both business services as well as the expansion of IPTV services into the mobile market.
“Security was not addressed in the original body of work that was IMS,” said Verizon’s Salas. “Today, we address security on an application basis, but we needed to think of security on an end-to-end basis because we move into an IP environment. If you want to preserve the customer experience in piecemeal, you will degrade the customer’s experience by having overwhelming security. We felt we needed to think about it end-to-end and build an architecture that could accommodate a sensible implementation.”
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