Dual-Mode Phones May Expedite IMS Development

The complex hand-offs and back-office capabilities inherent with seamless roaming may lure carriers to IMS for mobility among different access networks.

Whether people will be able to roam seamlessly from their homes to their cars to airports and cafes eventually will depend on intercarrier agreements and interconnections. However, the groundwork is being laid, as dual-mode phones and pioneering carriers are starting to allow customers to hop from WLANs to cellular networks within the same call or event session.

Substantial growth in the mobile work force and advances in IP telephony, LANs, WANs and cellular networks mean that seamless mobility among circuit and packet networks may not be too far off.

For landline carriers, VoIP and the evolution of data networks, Centrex and PBX are opening the door to seamless mobility. For cell carriers, WLANs and the convergence of voice and data services and networks are opening their eyes to the possibility of seamless mobility.

For that reason, dual-mode handsets are emerging from manufacturers like Motorola, Qualcomm, LG Electronics and Nokia.

Steps Toward Mobility and Seamless Hand-offs

“We found that 30 percent of all cell calls take place at home, and that 19 percent of GSM customers with BT Broadband have poor or no coverage at home,” says Ryan Jarvis, chief of convergence products at BT. To augment the coverage at home, the company created BT Fusion, which seeks to fuse the speed and quality of fixed networks with service features of mobile.

Additionally, Fusion draws BT into the triple play arena, as its fixed voice and broadband offerings now are complemented with mobile over broadband. The latter is enabled through its Vodafone partnership, which BT hopes sets the stage for leadership in fixed/mobile services. “Our goal is to be a quad player next year with the addition of our IP TV product,” says Jarvis. By layering BT Fusion onto other offerings, the company hopes to position itself as a leader in seamless roaming.

Although the service is still young, more than 20,000 registrations were generated by the press release for BT Fusion in mid-June. “We didn’t expect that,” Jarvis says, “as we hadn’t done any marketing for the product at that point.”

Despite the auspicious numbers, BT is being cautious­first rolling the service out to 400 customers, who received free Bluetooth-enabled Motorola V560 flip phones and hubs. A BT Fusion-enabled version of the Motorola Razr V3 will be available later this year. “We want to gauge the perceived value of dual-mode roaming for wireline and wireless customers before rolling out to the thousands who registered,” says Jarvis.

For now, BT is evaluating how long it takes customers to take the hub out of the box and how many calls to customer service the new product generates.

How BT Fusion Works

In 2G and 3G networks, mobile switches and base station controllers track mobile calls as they move from cell to cell. With BT Fusion, the dual-mode phones are equipped with antennas for both Bluetooth and Wi-Fi, which means that the devices can handle the transition from the more mature Bluetooth to the fast growing Wi-Fi.

BT will use the high-powered Bluetooth version for its first two launches. With Bluetooth, the devices can switch onto the wireline network, and as the signal is lost, flip to GSM through agreements with Vodafone to establish the call. “But, with 7,800 hotspots, the BT Fusion Wi-Fi handsets will be used next year as well,” says Jarvis.

BT Fusion hand-overs take place between the WLANs and the mobile network, realized through the Vodafone partnership. An IP connection is established via a small “mast” on the devices. The mast is a radio transmitter that looks like a base station controller to the network. That means the network thinks the mast is a cell.

“Rather than see a radio transmitter, it thinks it sees a broadband connection to a Wi-Fi device, and then it’s the mobile network that switches between the cell and Wi-Fi domain,” explains Malcolm Wardlaw, vice president of mobility intelligence and applications. “When a device comes within 30 meters of a base station, it thinks of the hub as a cell tower and switches to a cell network.”

The organization’s billing and mediation systems collect and correlate CDRs to monitor behavior, and QoS functions on the hub ensure that voice is optimized over data. “In the case there is a massive peer-to-peer play,” Jarvis says, “the Fusion mobile call will take priority.”

In reality, it is BT’s broadband network operating within the customer’s house or enterprise building. “The switch takes place seamlessly, and the user detects only a quick beep and a hotspot logo on the screen that says ‘BT Wireless Broadband,’” says Wardlaw.

As for billing, BT had two choices. “We debated whether to start off billing people according to where the call was first launched—on cellular, packet or landline,” says Jarvis, “or to bill for the time on each network type used in the same call.” For now customers have opted for the former, so they are charged according to the network on which they launched the call, even if they roam from the broadband network out onto a cell network. “We have to be sure to avoid confusing the customer experience with mixed features and separate bills, so we’re keeping it simple to draw customers to the service,” says Jarvis. “The decision to change the billing will depend on the profitability of the product and the way in which we position the service. It’s a marketing rather than a technology decision.”

While evaluating how to monetize dual-mode handsets, BT is active in the technology that is driving seamless roaming. BT advocates openness through Bluetooth and Wi-Fi as a participant in the UMA Consortium. “Open standards will be the enabler for Wi-Fi/SIP-based products, which we believe will track into IMS as part of our 21st Century Network initiative,” says Jarvis, reinforcing the notion that BT will continue with its huge investment in delivering IMS to fixed and mobile networks.

Additionally, BT co-founded the Fixed/Mobile Convergence Alliance (FMCA), which comprises 24 carriers with interests in fixed/mobile convergence. “We think the nearly half-billion subscribers represented by FMCA are a potential market for fixed/mobile applications,” says Jarvis, one of the chairs for the organization. BellSouth

A different approach is emerging in the United States, as BellSouth becomes the first RBOC to move out of the lab with a trial of seamless fixed-to-mobile roaming. After one year of R&D, the company has rolled out dual-mode Motorola CN620 devices to the public.

“We want to see if fixed-to-mobile roaming is particularly compelling in campus environments as employees roam from one building to the next, from one satellite location to the next,” says Mario Muth, senior product manager in BellSouth’s wireless products division.

To explore the possibilities, Bell South rolled out the dual-mode Wi-Fi/GSM device to 25 Grey Advertising employees in September, to enable access to VoIP over Wi-Fi and GSM.

With BellSouth’s service, the components are an 802.11a band, GSM for cellular, an Avaya IP PBX and a Proxim Wi-Fi access point at the customer premises.

Like BT’s technology, BellSouth’s dual-mode phones for now “trick” devices to work, but with a PBX.

The IP PBX extension switches from WLAN to Cingular’s GSM network when it senses that the Wi-Fi network or signal is getting weaker. When the quality degrades, the device tells the PBX to call it back on the GSM network, at which time the handset fires up the GSM radio. “For a few seconds, the PBX establishes a three-way call among the PBX, the GSM radio and the Wi-Fi radio, at which time the PBX switches the voice bridge to GSM and shuts off the Wi-Fi radio,” explains Muth. At that point, the screen changes color and a beep notifies the user that the network has been switched. As the person roams from one network to the other, the device authenticates the user on the radio server.

Billing

While on the cell network, BellSouth customers are charged Cingular “anytime” minutes, and when on Wi-Fi, they are charged for landline service. For the moment customers get two bills, with cell minutes put on their Cingular bill and Wi-Fi calls on their BellSouth bill.

“To expedite speed to market, we decided to go with the two different invoices, but ideally we would like to combine the two someday, so that Cingular Wireless customers see their call on a BellSouth bill,” says Muth, conceding that such convergence is more complex in wireless than in wireline. “We must modify billing systems to accept billing feeds from Cingular for that to happen.” That modification is currently happening with residential customers who wish to receive bundled Cingular-BellSouth bills.

“The enterprise billing solution requires a greater level of billing integration, however,” Muth says. For now, enterprise customers can verify Cingular and BellSouth bills against the IP PBX call logs.

Bell South believes that, for the time being, consolidation of devices will outweigh the desire for consolidated bills. Eventually, though, “customers will cut back considerably on the number of devices and bills they must handle with wireless-to-wireline roaming,” says Muth.

Sprint

To set the stage for seamless roaming, Sprint PCS wants customers to be comfortable with Wi-Fi data functionality on their CDMA handsets. It hopes to accomplish that by rolling out its Smart Device (PPC-6700), a PDA/phone-combination handset that tries to replicate the PC experience on a mobile device with Microsoft Windows Mobile 5.0 software, a full QWERTY keyboard and a 1.3-megapixel camera with video capabilities.

By combining wireless, Evolution Data Optimized (EV-DO) and Wi-Fi data functionality, Bluetooth Wireless Technology, email and Web access, Sprint’s goal is ultimately to have a common architecture serving both enterprise and consumer customers.

IMS is the architecture Sprint believes will enable seamless mobility between various access networks, according to Manish Mangal, senior manager in Sprint’s Technology Architecture Organization. “Because IMS has been built to be access-independent,” he says, “it will not break the services running on top of it.” Operators building the system will face optimizations and learning curves over the next few years, he concedes, “but it will be worth it once we have seamless mobility across any access network.” Mangal believes Sprint is better positioned to expedite the roll-out of truly seamless roaming because of its many access assets under the Sprint brand.

He also believes Sprint’s business mobility framework—a platform allowing third parties to interface on its network—enables enterprises to better leverage Sprint assets. “That gives them a choice to deliver their own enterprise-specific applications,” says Mangal.

Sprint has been working with IMS for more than three years now, including standardization efforts in 3GPP2. “We built the ReadyLink solution based on IMS concepts before it was standardized, and that gave us a head start on IMS implementation,” says Mangal, referring to Sprint-Nextel PTT service.

Sprint will employ a full version of the IMS subscriber profile home subscriber server (HSS), which “provides us an ability to store customer profiles in a common place and simplifies the provisioning and customer data management,” says Mangal. For example, as users add IMS-based services from Sprint to their subscription, updates occur in the HSS customer profiles that are accessed by back-office systems for billing and mediation.

Because records for bills will come with IMS, mediation will be needed to correlate them with those produced by the Sprint CDMA network. “Mediation and charging systems will play an increasingly important role in billing, as they would need to be application-aware,” says Mangal.

The BSS and OSS would need to evolve to support interfaces with the IMS elements, which involves significant development efforts, but Mangal does not anticipate a technical roadblock.

“It’s the intelligence to know where the user is at any time that will be the key,” says Mangal. As do many others, he believes the registration aspects of IMS will enable users to essentially “re-register” as a SIP client as the devices detect changes. In addition, a charging function is built into the network that generates a usage record of voice and data services. “It’s the knowledge of the user’s location at any point in time that helps determine the appropriate access network for particular calls,” he explains. “If the device is not in active call/service, you can trigger presence information. While in-call, the IMS architecture enables call control through mechanisms that ‘anchor’ users into the IMS network.”

As users move from WLAN to CDMA, a new call will be triggered, and the existing call will be diverted to IMS. IMS then does the context switch. That enables the leg of the call to change without affecting the continuity of the call.

“It’s the concept of the preferred roaming list that IMS introduces, so the client looks for the best network according to location. With dual-mode handsets that will enable devices to look for the preferred infrastructure, and then the second and third preferred network,” says Mangal.

IMS: Steppingstone from Mobility to Hand-Offs

The mobility found in today’s dual-mode handsets, however, doesn’t quite reach the ideal of a truly seamless hand-over. Some are hoping that the 3GPP’s IP multimedia subystem (IMS) will provide the framework for defining how carriers can deliver IP multimedia services over any kind of IP access--whether 3G, GSM, CDMA2000, xDSL, or WiMax. The hope is to eliminate the need for differentiating service types between wireless and fixed networks.

“There is an important distinction in IMS between providing ‘mobility’ and ‘hand-over’ functionality between circuit [CDMA or GSM] and Wi-Fi environments,” says John Scaldaferri, senior product manager for IMS products at Lucent Technologies, which is in the throes of approximately 50 trials of its IMS-based portfolio with 14 wireless and wireline service providers.

Scaldaferri defines the “mobility” aspect of IMS standards as the ability to support an end-client device—operating in the CDMA or GSM domains—to also operate in Wi-Fi environments. “End clients can migrate from one domain to the next—CDMA to Wi-Fi or the reverse, GSM to Wi-Fi or the reverse—provided the end-client user manually reestablishes the call when migrating into the new domain,” he says.

That type of “mobility” is not as easily obtained for “hand-over” functionality, Scaldaferri says. “With hand-over functionality, the end client’s established call is maintained as it traverses between circuit [CDMA or GSM] and packet [Wi-Fi] domains.” In other words, the call does not have to be manually reestablished by the end client user, as required with the aforementioned basic “mobility.”

Such functionality is still in the throes of development. Parties involved with IMS architectures are looking for bidirectional traversal enabling transparent circuit-to-packet and packet-to-circuit movement.

“There is ongoing work in the standards bodies to allow for this traversal to occur in a uniform manner and allow for the appropriate signaling to take place with the Home Location Register to support end-client user location updates and roaming,” says Scaldaferri.

Lucent engineers are contributing via the 3GPP SA Working Group No. 2 with proposals for the TR23.806 document, which begins to address more standards-based mechanisms to allow circuit-to-packet hand-offs.

Lucent plans to have packet-to-circuit hand-off functionality available early in 2006. “In addition, we will continue contributing to the standards efforts to more uniformly provide mechanisms to allow hand-off to take place when traversing from the circuit to packet domains,” says Scaldaferri.

Online and Offline Charging

With the introduction of this mobility, the IMS architecture with 3GGP Release 6 has defined mechanisms for providing robust off-line and on-line charging capabilities.

On-line charging may come into play when carriers make a foray from postpaid into prepay, or some hybrid of the two—for example, when parents desire a guarantee of control over kids’ text message services. Thresholds will be established along with advanced account management and active charging necessary for close-quarter balance management and marshalling of subscriber information against services.

If architecture recommendations for off-line charging capabilities are followed by IMS functionality, and if IMS accounting management architectures enable on-line charging mechanisms, those capabilities may be possible. “So far, there’s been a lot of progress with the introduction of the Charging Collection Function and the production of Diameter messages [over the Rf interface] from the Call Session Control Functions to the Charging Collection Function,” says Scaldaferri, noting that Lucent is enhancing its IMS accounting management architecture to offer on-line charging mechanisms. “With the introduction of the Ro [SIP] interface between the IMS Call Sessions Control Functions and the On-Line Charging Complex we are committed to this accounting management architecture, which ensures call events and CDR feeds coming from the IMS switching domain can be combined with carriers’ existing circuit-based CDR feeds,” says Scaldaferri.

That will enable carriers to correlate records with their existing billing mediation systems. “We don’t want customers to have to change existing back-office billing systems to support the off-line, and later the on-line, charging architecture introduced by the IMS network elements,” says Scaldaferri.

IMS facilitates that type of correlation by providing correlation tags in the call detail fields.

Today, most billing mediation systems handle correlation functions similar to those described above.

As service providers get into event-based and session-based charging, they will have greater charging flexibilities with their intended service offerings. But their services and billing architectures will have to change, to incorporate these functions into back-office and feature server applications.

“Manufacturers must evolve accounting management architecture to ensure the IMS architecture offered to service providers continues to support the billing dynamics of the advanced services and applications that service providers want to roll out,” says Scaldaferri.

Mediation and Billing

As switching vendors hash out correlation through IMS, the mediation vendors feel the ripples of what the equipment companies end up selling. “As equipment vendors sell IMS infrastructure to minimize the impact of converged services on billing and OSS, we will have to keep up with major areas related to charging for IMS,” says Openet founder and CTO Joe Hogan. “We will provide charging connections for offline charging and IMS online charging services when the demand is there.”

Already, Openet’s CCF online charging system has been released for use by equipment vendors. “OCS is in the call path to coordinate charging and rating controls,” says Hogan. “IMS-compliant equipment will set the connection and ask OCS for permission to establish calls after credit control and clearance is conducted.”

“As IMS causes rating and charging to come together, compliant nodes will ask for approval over defined, open protocols like Diameter,” says Hogan. Handoffs during a session’s progression generate Diameter messages, which are then taken from switching network elements (session managers and application servers). “Through Diameter, OCS is asked whether ‘it’s a go’ for a particular subscriber and service,” explains Hogan.

The charging system then sees the payment plan, the service required and optional services, as well as the credit available. “That means rating systems have to move closer to the network and inside the charging platforms,” Hogan says. To achieve that, Openet is working with Siemens and Lucent to embed rating into OCS, so rating can take place at the time of an order.

Real-time rating requires a way to piece together roaming transactions by finding elements of the signaling protocols used to enable roaming, such as through SIP for Wi-Fi calling and SS7 for wireless calling. The call attributes that enable a service provider to piece the transaction together are transmitted to a real-time charging architecture in the form of accounting protocols such as Radius and Diameter (see this month’s “Standards Watch,” pg 30), or they are transmitted via a traditional CDR process where they are post-processed and correlated. According to Bruce Grainger, VP of sales for Portal “It will be a puzzle, as carriers look at processes and duplicate records.

Carriers will need to know where records originated and track where they went.”

“Tags” help Portal to assemble the puzzle on CDMA and TDMA networks. “Once we get the CDRs and event data,” explains Grainger, “we sort information according to customer profiles through hierarchies established by customers and their partners. We then turn on TAP, and NCE records come in to rate and discount services.”

To further extract services from underlying technologies, mediation will need to have very robust correlation and aggregation.

How It Works

Charging data functions, in the charging gateway, correlate information and consolidate data into a single CDR per network element. Those CDRs are then sent in an ASN format to the charging gateway. That gateway takes CDR feeds and sends a single CDR per session to the customer billing and mediation systems, which then terminate into existing billing and mediation systems deployed within service providers’ back offices.

The CDRs then go into the same billing and mediation systems as do those from the circuit side of the equation. It’s the mediation systems that have to correlate the two sides, by acquiring files from telephone switches to deliver records to billing.

Mediation then takes the CDRs for correlation of data, which helps carriers decipher when calls were made and how they switched from one network domain to the other. It’s the logic in the correlation engines that help mediation collect caller identities and profiles of converged accounts, discounts and rates. That helps carriers charge for the GSM or wireline portions of the call according to their interconnect agreements.

Because of the sophistication of aggregation and correlation necessary with seamless roaming, Hogan recommends that carriers do as much as possible in the mediation layer to take pressure off billing.

“The ticket prices for billing are larger than mediation and charging platforms,” Hogan says. “The more you do at the charging platform the more you save, because many people and tens of millions of dollars are necessary to do correlation logic in billing.

“In charging, you depend on charging platforms to charge accurately at the time approvals are issued, so carriers need to identify where hand-offs need to occur and then massage CDRs to know whether or not specific calls involved third parties,” such as MVNOs or wireless or wireline companies.

Indeed, as traditional mobile operators or ISPs get into Wi-Fi, there will be more complex agreements. Making them transparent to the end-user and the back-office infrastructure is the challenge. According to Intec’s Scott Mackay, VP of solutions for North America, the settlement and interconnect that will be the biggest challenge. “Workflow components of service activation will be more important as carriers bring on new partners and elements. The activation systems will have to manage or add new workflows to their provisioning and activation agents, which becomes even more complex with real-time services,” says Mackay, referring to the fact that dynamic enabling of services will happen across multiple elements.

Mackay believes that before the FCC gets its arms around this emerging market, new settlement agreements will have varied models. “In Europe, models will be based on ITU,” he says, “and in the U.S. it will be CABS settlement.”

With those models, agreements will be point-to-point settlement agreements negotiated from one carrier to an ISP and so on to other partners. “That’ll mean, as the FCC gets involved, that systems will have to be dynamic to support the kinds of models pushed down from regulatory issue standpoint,”Mackay says.

According to Openet’s Hogan suggests that IMS-compliant systems could be a plus in satisfying regulatory powers that monitor how companies charge for converged calls. “When hand-overs and signaling are done on an open standard, the regulators tend to be more satisfied than if things are done in a proprietary environment,” says Hogan.

Operators will have to figure out what to do with the many homegrown systems still stuck in their back offices for rendering and billing. Whether such systems can be modified to handle event-based charging is questionable, since records and data from mediation will be far more sophisticated than before.

Revenue management, billing and rating of calls in dual-mode environments are a “new frontier,” according to Grainger at Portal. “Even though convergence is not a new concept, the ability to deliver voice, data and content seamlessly from network to network requires an ability to know all parts of a call, even though information is scattered over different pieces of the network.”

He believes the biggest challenge with dual-mode will be capturing all the pieces of a call or event and correlating them for a cohesive picture of what took place.

“It will be a puzzle, as you look at processes and duplicate records. Carriers will need to know where records originated and track where they went,” says Grainger. “Point solutions create a lot of silos, so a platform approach is necessary to accommodate new roaming scenarios.”

“As carriers get into dual mode, they want to avoid a huge rip-out or rebuild,” says Grainger, and for that reason they should seek out roaming modules that are plug-and-play. “That way, regardless of cable, wireless or wireline, everyone has the same type of core to work with to avoid major rebuilds every time there is a change.”