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Communications providers recognize the competitive imperative to deliver voice, data and video services over a common IP infrastructure. At the same time, wireless technology (cellular, WiFi, WiMAX) has emerged as the clear access preference for operator services in both consumer and enterprise markets. Fusing fixed and wireless access networks together to ensure seamless service continuity is a key challenge for operators today. This phenomenon is loosely known as fixed-mobile convergence (FMC).
While the market opportunity and business reasons for FMC are well documented, operators are faced with two seemingly competing architectures to deliver converged services: Unlicensed Mobile Access (UMA) and IP Multimedia Subsystem (IMS). The dilemma is clear — forgo UMA services and risk missing out on a potentially significant market opportunity, or deploy UMA services and risk significant time and network infrastructure investments that may not be IMS-compatible.
Regardless of the approach operators choose, they must clearly understand how the infrastructure solutions they deploy will help them minimize these risks, while aggressively pursuing the market opportunity for FMC services and delivering services without boundaries.
UMA: The First Wave of FMC
In January 2004, a group of GSM operators and vendors joined together to form the UMA Technology group (www.umatechnology.org/index. The goal was to provide GSM operators with a non-intrusive way to deliver GSM and GPRS services over alternative wireless access options. This effort resulted in the UMA specification, which was ratified for inclusion in Release 6 of 3GPP as the Generic Access Network (GAN), or TS 43.318. This first-generation FMC solution makes the existing GSM network view the UMA Network as a Base Station Controller (BSC). In doing so, it moves the voice traffic from the IP access network to the mobile operator core network. This solution leverages the operator’s existing network architecture to deliver services across fixed and mobile networks.
As an early effort toward convergence, UMA garnered the support of multiple GSM operators. These efforts are beginning to bear fruit, as there are more than two dozen operator trials globally. Handset vendors have also joined in the collaborative effort to bring UMA to market. By the end of 2006, there are forecasted to be several mass-market handsets available from major manufacturers, including Nokia, Motorola, Samsung, and LG. Availability of these handsets significantly increases UMA’s chances of gaining customer interest, as the price point of such phones, coupled with a compelling service offering, will make FMC services attractive for the average consumer.
From an operational perspective, UMA offers operators a compelling proposition in two ways:
1. It lowers carrier costs by offloading traffic from cellular radio infrastructure to low-cost IP networks; and
2. It creates more revenue opportunity by allowing mobile operators to increase indoor voice minutes.
In this respect, the technology makes operational sense, but many industry observers are concerned with UMA’s long-term viability.
The main concerns with respect to UMA include the fact that the technology was designed primarily for mobile operators, does not deliver any new services [beyond GSM voice, SMS, and basic GPRS data], and is not based on SIP. Each of these issues has legitimate roots and should be explored prior to operator deployment of the technology. As discussed earlier, the UMA standard was founded primarily by GSM operators and vendors to resolve issues related to indoor coverage. Its architecture also caters to mobile operators, as it moves the traffic from the unlicensed wireless network to the cellular core network. In this respect, it is not ideal
for a wireline carrier
that would like to put the traffic directly on
its backbone.
Many industry observers are concerned with UMA’s long-term viability.
The second concern is UMA’s limited ability to handle services efficiently beyond standard GSM. However, the bulk of today’s mobile phone use involves just voice and text messaging. Nonetheless, multimedia services are becoming an increasingly important differentiator among mobile operators and will likely be an important component of a carrier’s FMC network. This is a long-term consideration that operators should be aware of as they evaluate technology alternatives.
The third (and certainly the most strategic) challenge with UMA is that it is not based on SIP. This is a particularly relevant point because the IMS architecture leverages SIP as the underlying protocol. Since UMA does not use SIP, many regard it as a short-term solution that will not have lasting value as the carrier network evolves. This uncertainty leads many carriers to believe that they are choosing between UMA’s time-to-market advantage versus evolving their network toward the long-term strategic IMS architecture.
IMS: The FMC part
The IMS framework is being developed within the Third Generation Partnership Project (3GPP) and is designed to provide operators with a common service delivery platform across wireless and IP networks. This broad effort unifies network silos and allows carriers to rapidly offer a multitude of new services in a cost-effective manner. The IMS architecture relies on SIP as the underlying protocol
used for service delivery. Thus, IMS requires handover solutions
that leverage SIP to converge wireline and wireless networks.
Mobility within the IMS framework is currently under development and defined by 3GPP as the Voice Call Continuity (VCC) effort. The current draft specifies an approach that requires the handset to initiate a second call towards the Call Continuity Control Function (CCCF) to trigger call handoff between cellular and IP networks. This is an important first step for SIP-based mobility, but there is clearly quite a bit of work yet to be done, including how to address services beyond voice.
As the market evolves, specifications must address the mobility of services beyond voice, including data and multimedia. Additionally, issues, such as allowing carriers to centrally manage and enforce handover policies and establishing handover triggers based on bearer path parameters such as QoS, should be considered.
Operators worldwide recognize the efficiencies associated with IMS, and major vendors are rapidly winning trials and contracts. In fact, Lucent and Ericsson alone have announced more than 130 product related trials with nearly 35 operators. Many operators will have a FMC component as part of these IMS initiatives. Despite the progress that is being made in the IMS framework and mobility based on SIP, there are issues that must be worked through.
Many industry observers concede that SIP-based mobility solutions within the IMS framework are not yet ready for deployment. The primary reasons are the assertions that mass-market phones are not yet available, early standards proposals do not support services beyond voice, and that IMS networks are a distant reality.
While existing multi-radio smartphones are capable of leveraging SIP for mobility today, these devices are not yet available in a mass market form factor or cost point. This remains one of the critical limitations to SIP-based FMC deployments and a clear advantage for UMA, assuming handsets achieve volume shipments in 2006 as forecasted.
As the market evolves, specifications must address the mobility of services beyond voice, including
data and multimedia.
In its current iteration, the proposed 3GPP VCC standard only outlines requirements to support voice. This issue may not be a showstopper for an operator considering initial deployment, but it is problematic as operators become more reliant on revenues from multimedia traffic and as bandwidth requirements increase. When considering an architectural direction, operators should understand how their vendors will evolve to support delivery of multimedia services
over various wireless access networks, including the seamless handover of these complex traffic types.
Perhaps the most common argument against SIP-based mobility solutions is that the “holy grail” end-to-end IMS networks will not be built for some time.
While this statement is true, it does not preclude operators from deploying IMS-compliant FMC solutions ahead of completing their IMS infrastructure transformation.
Looking Forward
The reality is that FMC services offer operators a tremendous new market opportunity. Regardless of the approach, operators must manage the various risks and advantages associated with each alternative, including time to market, investment protection, and future compatibility. Selecting the right infrastructure will ensure UMA deployments have a clear path to IMS, while an operator deploying SIP/IMS-based FMC services can quickly leverage UMA devices should they be adopted in volume. 
Peter Wexler is vice president of engineering at Stoke (news - alert). For more information, please visit the company online at www.stoke.com).
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