All true Mobile UC solutions have a degree of core commonality as their base feature: They support a reliable level of active-call roaming between WiFi and cellular networks. From there, the list of features diverges, but true Mobile UC will also:

 

 

At the center of any Mobile UC purchasing decision, however, is the evaluation of two key capabilities of any solution: reliability and voice quality. Because of these criteria, exactly how the application implements Mobile UC’s core capability (WiFi-to-Cellular roaming) becomes the most critical path, or barrier, to a product’s success.

 

This paper describes the process involved in properly enabling smartphones to roam automatically and seamlessly, back and forth, between WiFi and cellular networks, while enabling value-add functions equally over WiFi and cellular. And more importantly, it discusses the potential complexities and pitfalls associated with seamless roaming and DiVitas’ unique approach to addressing them.

 

As there are currently no standards dictating how seamless WiFi-to-Cellular roaming should be accomplished, each solution will be unique in its implementation. Until now, there has been a lot of attention on the “who” and “what” part of the problem — who is considered to be a Mobile UC player and what their solution is called. But now the issue has become “how” these players — past, present and future — will approach seamless roaming. As it stands today, the available methods for true wireless network-to-network roaming fall into two basic camps:

 

 

DiVitas believes there is only one approach that will yield a seamless experience that meets the key customer requirement of reliability and voice quality — Environment-Aware (News - Alert)™ roaming. DiVitas has implemented the Environment-Aware approach because it is the best solution for providing an optimum voice experience in any type of wireless environment. DiVitas chose this approach because availability of an adequate WiFi signal is difficult to predict, and the mobile phone should always be prepared to seek the optimum available network (based on quality.)

 

DiVitas pioneered the concept of “Environment-Aware” WiFi-to-Cellular handovers to ensure seamless roaming without user intervention. In realistically assessing the target of wireless environments, change is a fact of life. Traffic flowing over wireless and Ethernet network segments ebb and flow, making the observed behavior of any point-to-point link dynamic.

 

In contrast, Location-Aware roaming determines when a mobile worker in a corporate WiFi environment has crossed the edge of a WiFi network, which triggers a roam to cellular. Such a design, however, fails to anticipate movement of objects in the office space (i.e., metal filing cabinets), which can interfere with, or cause congestion, the RF signal. Roam decisions based solely on location within the WiFi cloud cannot account for these network vagaries and can impact roam effectiveness.

 

DiVitas believes WiFi-to-Cellular roams should not be driven by “location,” but driven by a collection of “environment” conditions:

 

 

All of these scenarios are characteristic of different network conditions that impact the ability to provide the best voice quality to the user. Responding to these conditions in a dynamic fashion obviates the necessity of supporting any “location” awareness. Environment-aware roaming operates consistently, regardless of the specific network conditions in making the best network choice.

 

Solutions that employ location-aware roaming base it on the fact that location is deterministic (“we know when we are out of the WiFi cloud”). The rationale is that the handset and the appliance has a “location-awareness” and will not attempt roams to cellular as long as it is not within range of the identified roam-location. These “roam-locations” must be mapped to the hosting WiFi facility geometry by a manual configuration operation using a utility to mark the roam-locations such as building exits. Once in range of a roam-location, roam-decision logic is invoked that will trigger a roam to cellular when the signal strength drops below an acceptable level. Location-aware can be leveraged in some cases to extend battery life (through managing the WiFi radio). Once the roam to cellular is complete, the claim is that battery life can be maximized by controlling the rate at which WiFi scans (trying to find a WiFi net) are performed.

 

However, while Location-Awareness may assist you when you are roaming from WiFi to cellular (i.e., leaving a building), it’s actually a hindrance when you are trying to roam in the other direction — from cellular to WiFi. This is because your smartphone isn’t getting the Location-Aware help it needs to connect with a WiFi network, so your phone must work extra hard by constantly seeking a WiFi signal. If this process is too frequent, it will quickly run down the battery. At the same time, if it’s too infrequent, “finding” a WiFi network will be delayed, and this threatens to increase use of cell minutes.

 

As illustrated above, assumptions about RF stability or availability based on location are not always valid. Many factors impact the WiFi signal, which in turn invalidates assumptions made by this technology. Network congestion (created by applications competing for bandwidth), dead-zones in the corporate WiFi environment and general degraded network conditions are all issues that impact the ability to sustain high voice quality. With Environment-Aware roaming, these types of changes in the WiFi environment will not prevent the Mobile UC application from taking the right action to roam to the most stable network in order to sustain the call.

 

Environment-Aware: With an Environment-Aware solution, any time the voice connection viability is jeopardized by RF congestion or interference, a roam to cellular should be invoked. For example, a wireless voice connection may be initiated when the signal strength is strong and congestion/interference is low. But if a high-bandwidth wireless application is launched, the RF characteristics radically change, deteriorating the voice quality experience. At this point, the handset will roam to cellular, even though the user is located well within the bounds of the WiFi coverage area, in order to ensure maximum call quality.

 

The Environment-Aware approach ensures that the user has the very best voice quality experience by monitoring the total RF environment in order to make roam decisions. RF can be dynamic, irrespective of location.

 

Location-Aware: Problems arise when the solution – as with products based on Location-Aware services – don’t completely address real-world network problems for sustaining the best voice quality. Because the wireless environment is constantly changing, it is important to design a Mobile UC solution to support that state.

 

Deployment of WiFi into virtually any facility will be challenged with a coverage problem. The geometry of the building or construction materials may result in areas that have no coverage (i.e., “dead zones). For example, a WiFi network may deploy omnidirectional antennas for signal shaping. This means there are two “locations” identified where a handset would commence a roam to cellular upon exiting the building. There are also two areas within the building that have no WiFi coverage and, if a location-aware handset were to enter this zone, there would be no indication to roam to cellular if it was not a marked “location” and the call would drop.

 

Such “dead zones” can occur as an artifact of the WiFi deployment where the Access Point (News - Alert) (AP) placement is not optimized. They can also occur if any structural or equipment changes are made to the building interior – which is quite common – after the wireless system is installed. RF opaque material such as walls, desks, filing cabinets, mirrors, or cubical walls may affect the RF coverage areas, creating “dead zones” that may require a re-survey of the building to achieve adequate coverage.

 

If a dual-mode phone based on a Location-Aware solution wanders into a dead-zone, the phone will drop the call because suddenly there will be no wireless service available. The only option available to the mobile worker is to step into WiFi coverage and re-initiate the call.

 

APs often experience overlapping channel conflict - an occurrence that happens when two APs configured to the same channel are located side-by-side. When this happens they can either null each other’s signal out or induce interference, blocking communication.

 

Environment-Aware anticipates problems: Whether there is a loss of WiFi signal or degradation of voice-over-WiFi quality caused by situations like overlapping channel conflict, Environment-Aware will automatically roam to cellular. This means calls won’t drop.

 

Location-Aware (doesn’t anticipate channel conflict): As with dead zones, a location-based solution is not able to roam to cellular when it experiences a loss of signal so the call will drop. With 802.11b/g, there are three RF channels that the FCC (News - Alert) permits to be used in North America: #1, #6, & #11. A layout designed to blanket a facility with WiFi coverage, using only three channels, can easily create co-channel interference.

 

Because the two APs are assigned to the same frequency channel and their coverage overlaps, a zone of interference is created at that point. A mobile device positioned within the coverage overlap area, may have a solid association with on of the APs, but will encounter so much interference that the quality of the link may degrade and voice quality will suffer. Because the mobile unit is not positioned at a location-point (using Location-Aware intelligence), the phone may not choose to roam to cellular, and the user could end up dropping the call because of poor voice quality.

 




 

At any point within range of an operational WLAN, there is the possibility of encountering points of congestion. Heavy traffic through the local access point or even at the router/switch level can severely impact voice quality of a mobile device. For example, a nominal case where a mobile device is competing with other devices for bandwidth at the AP. Escalating packets/second-rates impacts the effectiveness of an AP’s ability to process data and, under heavy loads, it will begin to drop frames. In such scenarios:

 

Environment-Aware: Mobile device will automatically roam to cellular.

 

Location-Aware: Sustaining a call would be dependent upon a layer-2 roam to a neighborhood AP, but often the neighborhood AP is also congested or out of range. Depending upon the source, this general network congestion can impact all APs that may be configured with the system.

 

Part of being able to respond to changes in the wireless environment is the ability to monitor not only the signaling events but, more importantly, network changes that impact the audio quality.

 

Environment-Aware: Monitors both ends of a call (source and destination) and makes the best voice quality roam decisions based on the observed conditions.

 

Location-Aware: Typically segregates the call signaling (setup and termination) from the audio stream, which diminishes the ability to respond to environment changes. In this case, the mobile handset is the single point in the ecosystem that can monitor the real-time.

 

Environment-Aware: An Environment-Aware solution like DiVitas is always at the ready when it comes to hotspot roaming. DiVitas continually seeks the optimal connection, which means you can communicate via smartphone whether you are in the office, at home, or at a hotspot such as Starbucks, the airport or on a busy city street covered by metro WiFi. Environment-Aware means you are constantly connected to the optimal, available network, whatever — or wherever — that may be.

 

Location-Aware: A major pitfall with Location-Aware-based Mobile UC is that it is not hotspot-friendly. If you enter a hotspot, such as Starbucks or an airport, Location-Aware makes you wait for a very long time before your phone will ever realize that WiFi is available. The reason for this extensive delay is that although the handset may detect ten available APs in its range, it needs to investigate each one individually — and it needs to send the information on each AP back to the server for confirmation. This is a very CPU- and bandwidth-intensive process, which causes roaming delays, and it wears down the battery as well. In the end, Location-Aware roaming tends to be confined to a campus that has been Location-Aware-mapped (in a mapped environment, the site has been surveyed and the exits of the Location-Aware environment have been identified).

 

In contrast, DiVitas employs a “make-before-break” method of seamless roaming, which means that it doesn’t terminate a session until it detects a new, optimal connection. This is ideal for roaming seamlessly and automatically. Also, DiVitas lets the handset decide whether or not any AP in range will provide the optimum connection. DiVitas doesn’t rely on the server to make this decision, which eliminates problematic to-and-fro bandwidth congestion or unnecessary, intensive CPU usage associated with Location-Aware.

 

In order for Location Aware-based technologies to work well, WLAN systems must pass location awareness to a handoff server — typically through a mobile client. What about all the WLAN systems (already deployed or being deployed) that do not possess the ability to pass location awareness to a handoff server? These non-location aware WLAN systems comprise the vast majority of today’s market. In these cases our Environment Aware technology is the ONLY system that would work seamlessly.

 

Just recently ratified, the 802.11k standard is intended to improve the way traffic is distributed within a network by providing information to discover the best available AP (to understand the “neighborhood”). This is the standard by which WLAN vendors will implement new software that will pass the much needed information to a location aware handoff server. This information is core to ensuring Location-aware technologies do not accidentally roam to an AP that is already too busy. Today, no WLAN or handset vendor has implemented this ratified standard, making location aware seamless roaming less than seamless. Environment-Aware does not depend on the WLAN passing AP state information to a hand-off server through a mobile handset. Instead the mobile handset evaluates the environment at large and makes the decision about when and where to roam based on current voice quality conditions.

 

Location-Aware has historically been the defacto standard for handling roaming between WiFi and cellular. Although it has done a great service in making the transition as seamless as possible, DiVitas believes that there is a now better approach. Environment-Aware is proving to provide a superior and more consistent voice quality experience overall. Put simply, the main difference between the two approaches is that Location-Aware requires a static defined environment be in place and Environment-Aware assumes constant change. Given the state of most companies, change is one thing that can be counted on, and it is because of this that DiVitas put its smart minds into engineering this new, patented technology.

 

-----