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August 2007 | Volume 10 / Nuber 8
Feature Articles

Fixed-Mobile Convergence

By Richard Grigonis

Whether you identify it with IMS (IP Multimedia Subsystem), VCC (Voice Call Continuity), UMA (Unlicensed Mobile Access), or CBC (Cellular-Broadband Convergence), the concept of Fixed-Mobile Convergence is here to stay, thanks to its ability to deliver the same services to you regardless of whether you're connected to your fixed or mobile network. But the big question is, “To Dual Mode or Not to Dual Mode?”

“In the Wireless part of the market, FMC is now called Cellular-Broadband Convergence,” says Anand Parikh, Vice President of Business Development and Wireless Solutions at Sonus Networks ( “But whatever you call it, it's about one handset getting the same services anywhere, and we see that there are three ways to provide FMC as this technology has emerged in the market thus far. One is IMS-based FMC, and that came from the 3GPP standard for VCC. The second method is what the UMA technologies in the GSM world offer, particularly in Europe; UMA being the first way that FMC services were planned to be delivered to the market before the IMS or 3GPP-based VCC standard took hold. The third and newest method is FMC based upon femtocells and picocells, the tiny radio interfaces deployed in a residential subscriber's home that resemble WiFi access points but are essentially indoor miniature cellular base stations that connect over DSL or other broadband backhaul to a mobile core network.”

“All these three methods have differences in terms of what they bring to the table, but basically they all focus on providing the same kind of services to a single handset, whether you are using it fixed or mobile network. The underlying technologies are different, the impact on the handset is different, and of course the impact on the networks necessary to support these technologies is quite different as well.”

Ajay Gupta, Vice President of the Wireless and Convergence Business Unit at Aricent ( says, “There are three basic FMC technologies and each one presents a different set of challenges to be implemented, either in the network or in handsets. If we look at VCC, which basically allows you to connect to any IP network, if you don't have access to an IP network, you can switch over to a GSM or CDMA network. It makes use of SIP [Session Initiation Protocol] such as SIP-over-WiFi or IMS-over-WiFi. The technology is pretty straightforward and simple to implement in terms of developing products, except that, on the handset side, it presents a challenge when you want to switch between, say, GSM and VoIP. You need certain technologies within the handset for it to operate, such as SIP or IMS clients, plus you really need the handset to be dual-mode to handle WiFi, which means it will use a lot of power. The network side of the technology is not complicated and is fairly straightforward. The challenges are really on the handset side.”

“UMA has gone through many trials and has been used in the T-Mobile network and France Telecom,” says Gupta. “It presents its own set of challenges, but it has been adopted as a 3G standard. Still, baring very few companies such as Alcatel and Kineto Wireless, UMA has been promoted too much.”

“As I said, femtocell technology is really interesting,” says Gupta. “It doesn't demand any change in the handset. You can still work with a 2G or 3G handset. Instead of a WiFi router you use a 3G-based router which sits in your home and it communicates on one side with the IP backbone, getting all of your voice traffic over IP. On the other side, it interworks with 3G technology, particularly your handset. This I believe is potentially one of the best solutions apart from VCC, because there's no change needed on the handset side, but the challenge is: how do you create channels for these devices which will allow consumers to build their own network? It also means that the governments will have to provide low power spectrum operating in a given range. Moreover, will the operator manage these devices, or will it be like a WiFi router and the consumer will do some management by himself?”

“As far as Aricent is concerned, we have a fairly dominant play in the femotcell and VCC spaces,” says Gupta. “We don't have a deep investment in UMA, though we have a few customers.”

To Dual Mode or Not to Dual Mode?

“Will dual mode devices become popular? It depends on the network operator,” says Aricent's Gupta. “For example, some of the customers we work with are network operators. Some of them favor femtocells, but some broadband operators today offer broadband services and they want to offer WiFi at home, and they prefer VCC solutions. It depends on the nature of the operator or customer. There's no clear verdict as of yet.”

At Stratus Technologies (, Ali Kafel, Vice President of the Telecommunications Division, says. “The industry has talked a lot about FMC in terms of dual mode devices. In Germany, Deutsche Telekom wasn't immediately successful in offering dual mode service, but then Orange [formerly France Telecom], Neuf Cegetal and Iliad had a bit more success in rolling out their own services that can switch between cellular and WiFi networks. Their approach also uses a dual mode device. We're not talking about a multi-device phone system - it's a dual-mode single device phone, which some people love. Other people, such as myself, don't want to give up their favorite device. For example, I use a BlackBerry and I don't really want to give it up just because of a new service. But if I can use a service that works with my BlackBerry and my IP desktop phone, then I'll be very interested in it. That's the approach that we take here at Stratus.”

“We believe that FMC needs to be not just tied to a dual-mode device, because some people want to use their existing device and want the ability to hand-off calls from one device to another,” says Kafel. “That's what we're doing technologically. When you call me on my IP phone, I have the option to provision it as a subscriber; I can go on the web and specify that when a call is made to this number, ring all the devices that I have either simultaneously or sequentially. I can then pick it up and transfer the call from one device to another and the caller won't realize that I have done so. That ability is what I believe is a major requirement in the industry, to be able to go from one device to another, rather than just rely on a dual mode device that roams from one type of network to another.”

Single Identity, Single Device

One proponent of dual-mode devices is Luc Roy, Vice President, Mobile Enterprise, Siemens Enterprise Communications (

“Siemens Communications is actually two entities,” says Roy. “First, you have Nokia Siemens, which is focused more on the carrier space and deals with IMS, and then there's Siemens Enterprise, which, as it name implies, focuses on the Enterprise. I represent the Enterprise, so I won't address IMS to any great degree. But, interestingly, within the Enterprise division, we've actually just launched our FMC solution, which is independent of the carrier and agnostic to any RF [Radio Frequency] technologies. It supports GSM, CDMA and it's implemented by the enterprise at its own pace. IMS is taking longer to implement than many people expected, customers are looking for an FMC solution predominantly not so much because they want to save cellular minutes, but it's more about having a single identity, such as a single phone number, a single voicemail. Also, if I as a user enter an environment where there is a wireless LAN and I have a dual mode device, then whether I'm having a conversation or not, I want to automatically roam to my wireless LAN and maintain my single identity, so my dual mode device is represented by a single phone number and single voicemail box, which is basically my PBX phone number and the voicemail system it uses.”

“I've talked to about 40 enterprise customers in the U.S. and all of them don't want a Centrex-type solution because unified communications is so strategic to them that they are investing more with the PBX - for example, making it SIP-enabled because SIP is becoming the standard for communications, whether it be voice, video or messaging,” says Roy. “So they're investing a great deal and they don't want to lose control. They're not interested in getting a cell phone number representing the company's identity; instead, they want to retain their PBX phone number as their single identity and add that number onto their business cards, not a cell phone number.”

“FMC makes a lot of sense in the enterprise because that concept of a single phone number/single voicemail leads to more productivity, and better reachability,” say Roy. “With some of the early trials we've already seen some increased revenue because of FMC. People are now more reachable and can close deals right on the spot. So what we've decided to do at Siemens Enterprise is to create a solution that is totally independent from the carrier. The only thing you need from the carrier is the dual-mode device. Once you've got that, then we've provide the entire infrastructure of PBXs, wireless equipment and FMC capability, which we call the HiPath MobileConnect FMC solution for seamlessly unifying fixed enterprise VoIP, Voice over Wireless LAN [VoWLAN] and cellular networks.”

At Sylantro (, Frank Falm, Vice President of Marketing, says, “FMC can be interpreted in a number of ways. One way is in terms of the IMS network. One of our customers, Swisscom, services both fixed and mobile simultaneously, and they're just building out their IMS infrastructure with Sylantro and Ericsson. They have a very specific program where they have a purely fixed-line service and a service that's purely for mobile, and then they have a service that serves both of those simultaneously. That's a form of FMC where you have just one phone number that's now available in both fixed and mobile domains, and the same applications are available in both domains too. How often have you wanted to have just one phone number? Arguably, that’s a form of FMC that's extremely feasible in the marketplace and it's something that users understand. You call that the 'seamless mobility with single mode devices' definition of FMC. Basically you're talking about mobile extensions to business or home phones from the server.”

“FMC can also be defined more in terms of IMS and 'seamless mobility with dual-mode devices',” says Falm. “In the IMS world you have VCC, or Voice Call Continuity, defined by the 3GPP standards guys, which provides a flavor of that. That's also feasible, and it’s what we at Sylantro had worked on with a client vendor called FirstHand Technologies. At the client level, FirstHand monitors signal strength and they initiate the handover of voice calls to achieve the 'seamless mobility' function. Calls can start on the WiFi side and roll over to the cellular side. There's also logic in there to initiate the call on the cellular side and pin the call through a Sylantro server so you can handoff to the WiFi side. That handoff is achieved through the Sylantro API called Synapps, and a fixed mobile application in cooperation with a client developed by FirstHand.”

“Aside from this form of FMC, a huge variety of vendors out there provide similar seamless handover functionality at the network level,” says Falm. “The guys playing in the VCC space who are building VCC servers can include the likes of Bridgeport Networks, Outsmart, and so forth and then you have NewStep Networks, which has a flavor of that too. Still, the question becomes: how viable is seamless handover? Will it be massively adopted or is that something that's interesting for a certain class of people? One thing we have seen is that, for the most part, people don't want to pay for this function. If it happens, they expect it to happen for free. It's not viewed as a high value service but it's definitely something which can greatly improve certain scenarios.”

“What we see as being more interesting is the single-mode device model where your mobile device now participates as part of your business or in a hosted service,” says Falm. “That's considered to be high value because people are familiar with their devices and plans. Dual-mode makes sense in an area with very limited coverage. In fact, I'm speaking to you from Vienna, Austria, right now and if I had one of these dual-mode devices or a WiFi device here in my room, I could easily use that to place and receive phone calls through the network. So there's a case where I don't want to pay the roaming fees of three dollars a minute over here and I could in fact leverage a WiFi/broadband connection to achieve the same functionality. So there's a huge value and savings in being able to do a sort of 'long distance remote'.”

Testing for FMC

Certainly to make FMC successful, a great deal of testing at the vendor and network level will be necessary. At Azimuth Systems (, Jeff Abramowitz, Vice President of Marketing, says, “Azimuth's standardized wireless test solutions enable research, development, quality assurance and ultimately better marketing. Engineers can test the performance, conformance and certification of wireless devices and networks supporting data, voice and video applications. We've focused on wireless IP engineering test equipment. We're a major player in the WiFi space. Anybody who's anybody in WiFi uses our equipment, and now we've added WiMAX capability. We supply to the WiFi Alliance and Cisco, and we've garnered some design awards, and so forth.”

“The Azimuth approach follows what most companies do for wireless testing in their own labs,” says Abromowitz, “but with the added benefit of Azimuth having standardized this equipment. We put products in shielded enclosures that we call RadioProof™ enclosures, and we enable real access points to talk to real handsets. We simulate motion with our patented SmartMotion™ technology that uses precision attenuators to simulate how a handset can move away from an access point. We can even simulate motion in a controlled environment where hostile conditions such as traffic, interference, multipath, etc., can be introduced. Our Director software controls all of this functionality, and our Studio software allows people to share it. At a very high level, we sit at the intersection of testing data communications and wireless communications. Our mission is to provide these standard tools that enable customers to build product that are higher quality and that will shorten the development time for customers bringing their products to market.”

“We have two categories of system products, one that we call System Test platforms and the other is Channel Emulator,” says Abromowitz. “The key distinction between these two types of platforms is that a System Test Platform has what we call a static channel; you're basically cabling from one device to other and the only thing encountered in that channel is straight attenuation. The System Test Platform allows customers to test not just point-to-point but point-to-multipoint or even multipoint-to-multipoint. That's different than a Channel Emulator, which you can visualize as just a big bank of digital signal processors that you place between an access point and a handset. That bank of signal processors mimics reflections, attenuation, things moving around in the real world so that you can do controlled performance testing of a device against an access point. If you take a handset to a house, apartment, or commercial building and then you walk around each location, even if you have the same handset and the same access point, the handset's performance will differ because each environment is different. If you want to truly characterize the performance of the handset, you'd have to visit many locations. Our Channel Emulator basically does that. It uses the IEEE 802.11 models to replicate SOHOs and so forth. With the emulator, vendors can thus do rigorous testing.”

“Carriers are looking for excellent call quality,” says Abromowitz, “avoiding dropped calls and long battery life. All of that sits on top of standards, performance and industry certifications. The challenge is that certification doesn't necessarily imply anything in terms of performance, so you can have devices that are both certified and yet have vastly differing performance characteristics. That difference gets magnified if you start looking at phones as opposed to PCs or other data devices. When comparing home versus public access environments, you may find that a phone has different ranges from an access point.”

“So, for vendors that are testing the WiFi aspect of FMC in their phones,” says Abromowitz, “they need to test both the voice quality - yielding the Mean Opinion Score data - and the data throughput over range. They need to do 'cabled testing' because that's the way you get repeatable test results. And vendors also want to do 'open air' testing because that's how the end user will ultimately experience the product. Interestingly, in the cellular space, most testing is done in a cabled environment and spot testing is done in an open air environment. In the WiFi space, open air testing is what's most often done. Our expectation is that testing procedures will move toward cabled environment testing and spot checks will be done on open air testing.”

“Interference and loading on the system will also obviously affect handset performance,” says Abromowitz, “and then of course there's the notion of multipath versus non-multipath, and having a 'fair' channel versus an 'unfair' channel also affects a product's performance. Things can get quite complicated.”

At another great testing vendor, Tektronix (, Keith Cobler, Marketing Manager for Network Management, says, “Some people think of fixed-mobile convergence as an end-all technology, and others think of it as a stepping stone towards IMS. Depending on your current business model, you may have a different interpretation of where you stand. For many carriers, FMC is all about roaming with voice from fixed to mobile environments. Tier-1 operators are very much convinced about IMS and they're heading down that path. For many of them, FMC is an easy way to 'test the waters' because there's been an overall promise, from the consumer side, of having services and applications anytime, anywhere. So FMC is a nice 'proof point' for a lot of the larger tier-1 carriers to better embrace that concept.”

“From our side we've worked with many network operators and FMC is indeed a stepping stone toward IMS,” says Cobler. “For others, FMC is all about voice, because that's what their business model calls for, and now they've got the added benefit of combining some type of dual-mode device, such as a WiFi/cellular handset, where you can address both customer environments. So, yes, there are several definitions for FMC and many ideas as to where it's headed.”

“UMA is the GSM 'flavor' of FMC,” says Cobler. “It's really FMC for an operator that's following the GSM path, and it's looked upon as a less expensive alternative to IMS. IMS can be a bit scary if you're an operator and you want to deploy it throughout your entire network. That's a very expensive proposition to take on. In general, the operators' mindsets are beginning to change and the consumers will drive the network transformation. Let them choose the applications and if those apps are successful, then you build whatever network it takes to support those applications. In that sense, FMC is a good stepping stone in that direction.”

The general consensus is that IMS/VCC is the long-term heir apparent to providing FMC functionality, but femotcells and picocells appear to be a 'dark horse' technological candidate that may yet surprise all of us. IT

Richard Grigonis is Executive Editor of TMC's IP Communications Group.

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