Enabling Mobile Intelligent Roaming Across Networks

By  Rochelle Brocks-Smith, Manager, Mobility Solutions, Cisco — August 20, 2008

Business mobility is no longer an exclusive perk for sales teams and executives.

With the explosive growth of today's mobile workforce, business mobility is increasingly necessary for maintaining effective business communications. Users want to be connected to the contacts and resources they need to perform their jobs whenever and wherever work takes them. Undoubtedly, the adoption rate of dual-mode devices -- those that provide users access to services and applications over Wi-Fi and cellular networks -- is playing a significant role in driving this trend.  Infonetics Research estimates that dual-mode phone shipments will reach 285 million units by 2010 (Source: Infonetics Research, Inc. Wi-Fi Phones Equipment Market Share and Forecast, 2006).

With this increased reliance on mobile devices, creating a consistent mobile communications experience -- one that enables mobile employees to work and roam transparently, regardless of network topology -- is becoming a key challenge for enterprise I.T. departments.

This article explores three of the leading strategies for supporting seamless handoff capabilities, and the importance of an integrated approach that leverages the intelligence of the network infrastructure, open third-party partnerships, and ubiquitous access to enterprise business applications.

Top Three Enterprise Handoff Strategies
While a number of strategies exist for facilitating the handoff of mobile communications between cellular and Wi-Fi networks, three primary approaches are prevalent within enterprise deployments. Each approach provides some benefits for supporting business mobility, but the overall value of delivering mobile intelligent roaming depends on the extent of network and client software integration and control.

Enterprise Wireless LAN Infrastructure-Controlled Handoff
In the first approach, network connectivity of dual-mode devices is monitored by the enterprise wireless LAN (WLAN) infrastructure which controls the initiation of the handoff process. Consider yourself in the midst of an active call on your dual-mode phone as you leave your office building. As you approach the lobby door, the network detects that you are reaching the edge of the enterprise WLAN coverage area as the Received Signal Strength Indication (RSSI) power level of your phone drops. This initiates a software-based trigger to handoff your call to the cellular network. The handoff process may consist of a SIP proxy signaling request to the enterprise IP-PBX to create a new call leg through the cellular network to your dual-mode device.

This approach achieves call continuity with a broad range of dual-mode devices because customized client software is not required to determine handoff requirements. However, the tradeoff for offering end users a greater choice in devices is a less reliable, less seamless mobility experience. For instance, without specialized client software, activating a new call leg through the cellular network will require the user to manually answer a call-waiting tone. Additionally, the WLAN cannot detect voice sessions running inside an encrypted tunnel, such as a Virtual Private Network (VPN), decreasing handoff reliability.

Mobile Client-Controlled Handoff
In the client-controlled handoff approach, the client software in the dual-mode device is fully involved in the handoff process with minimal participation from the WLAN infrastructure and enterprise IP-PBX. Consider the same scenario described in the infrastructure-controlled approach but, in this case, the client software monitors the RSSI power level and initiates handoff to the cellular network.

While this approach offers deployment flexibility across virtually any WLAN infrastructure, it limits users to the devices that support that particular client software. In addition, when an enterprise has deployed multiple access points with dynamic power levels, the client software does not have access to this information from the network, and will be unable to determine an accurate handoff threshold. As a result, this approach could result in unpredictable handoffs and could lead to a frustrating user experience.

Mobile Intelligent Roaming Handoff
The third approach combines the best of all worlds. It leverages the intelligence of the wireless LAN infrastructure and the enterprise IP-PBX and closely integrates with the client software of the dual-mode device to initiate a handoff trigger based on the most comprehensive information available.

As mobile workers roam from the WLAN to the cellular network and vice-versa, the corporate WLAN has the most accurate information regarding the strength of the signal, availability of the network, and its quality of service (QoS) to support the running applications and types of devices being used. Integration with the enterprise IP-PBX lets users benefit from the same business applications over a Wi-Fi or cellular network by anchoring user connectivity through the enterprise network.

As mobile workers move between networks, the enterprise network still has the information needed to control hand-in or handoff of active communications and applications access. On the client side, leveraging the specialized software running on a dual-mode device enables accurate interpretation and facilitation of the handoff trigger for supporting data, as well as voice devices. While dual-mode phones are the most popular device today for mobile roaming, organizations may need to support a broader range of devices; thus, being able to interface with the client software of multiple, heterogeneous devices to interpret a handoff trigger will be important.

Integrated Approach Enables Transparent Mobile Experience
While each approach offers certain advantages for achieving voice handoff, enabling a truly transparent mobile business experience is about more than just call continuity.

The expectation for seamless mobile roaming today is that it will provide a consistent, reliable, and feature-rich experience that makes the location and circumstances of the mobile worker's environment irrelevant.

To meet these requirements, I.T. managers must consider an integrated approach to business mobility that moves beyond the best efforts of a WLAN infrastructure-controlled handoff or a mobile client-controlled approach.

The Mobile Intelligent Roaming handoff approach leverages the intelligence of the network, the ability to extend enterprise applications beyond the WLAN and allows open integration with an ecosystem of partners for optimal deployment flexibility, performance and investment protection. Using network parameters such as the location of access points in the network and client load provides the most accurate and reliable coverage information available to perform intelligent handoff triggers. Combining this information through an open Application Programming Interface (API), with third-party solutions, offers device and application innovation and positions enterprises well for future enhancements.

About The Author: Rochelle Brocks-Smith is Manager, Mobility Solutions, Cisco.

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