!WiFiOffload Evolution 130 0011 003

Wi-Fi Offload EvolutionA Practical Approach to Leveraging Unlicensed Spectrum to Offload Your RAN

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June, 2012

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Wi-Fi Offload Evolution

Table of Contents

The Business Problem ....................................................................................3

The Advantages of Wi-Fi ................................................................................3

Evolving Offload Solutions .............................................................................4

Phase I: The Enabled Client ...........................................................................5

Emergence of the Policy-Driven Client ..........................................................5

Phase II: Mobile Edge Enabled...................................................................... 6

Phase III: Converged Mobile Core – Seamless Services ..............................8

Compelling Solutions Are Required ...............................................................9

Conclusion .....................................................................................................10

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The Business Problem

The communications industry is undergoing a major revolution in which data, rather than voice, is the main network dimensioning consideration and driver of traffic growth. For example, today’s network users have grown accustomed to being “always connected” to the Internet regardless of location, and the increasingly preferred device is a wireless device. This shift in user requirements, combined with the latest genera-tion of high capacity devices, longer device battery lives, and new bandwidth-intensive applications has contributed to soaring demand for mobile broadband data and placed intense pressure on mobile network capacity. In some cases this has negatively affected service delivery by way of dropped data sessions and slower speeds, which has increased subscriber frustration. The mobile network operator must now deli-cately balance adoption of new revenue generating data services against the costs of building additional capacity to maintain service levels and grow the number of subscribers.

Wi-Fi has emerged as a viable network access alternative with a proven business case to relieve network congestion. However, questions still remain on how best to incorporate Wi-Fi into 3G networks while maintaining a quality user experience, retaining operator differentiation and the provision of legacy services since standalone Wi-Fi access does not integrate with the existing infrastructure.

This paper discusses effective and comprehensive solutions capable of addressing congestion and net-work capacity problems which improve the user experience and enhance carrier loyalty. Three phases of mobile data traffic offload are described, including the technology requirements and features available at each phase, and the resulting benefits of each to the mobile operator.

The Advantages of Wi-Fi

Wi-Fi has the ubiquity and spectrum characteristics to make it as attractive to operators as it is to end-users.

Firstly, it is widely available on a variety of devices. An estimated 245.9 million Wi-Fi portable media de-vices globally (125.5 in Europe) were in use as at the close of 20101. In the USA, the forecast is that it will reach 66% of all mobile handset shipments in 20152 with all new data hungry devices such as smartphones and pads having Wi-Fi as standard.

Secondly, Wi-Fi is currently deployed widely within the home and in public hotspots and business environ-ments. Since over 70% of mobile broadband traffic occurs indoors , this makes unlicensed Wi-Fi spec-trum essentially “free” to operators and often available at no charge to end-users. Wi-Fi, in particular is more efficient than 3G for large file downloads in terms of battery usage and duration of signal. Thus end users enjoy a better user experience through higher data throughput. For example, users attached to Wi-Fi networks can connect at speeds of 50Mbps or more on the air interface and, depending backhaul connec-tions, this can be delivered end-end through to Internet services.

Lastly, Wi-Fi has already been proven to successfully extend 3G network coverage and increase market share: In the United Kingdom, O2 successfully included Wi-Fi to meet regulatory coverage requirements for their 3G license by simultaneously launching the iPhone with Wi-Fi network offload, thus reducing the need to grow their network capacity whilst creating an upside to their 3G investment.

Altogether, Wi-Fi has the cost structure, ubiquity, and user acceptance to make it an ideal augment to the Radio Access Network (RAN) of mobile operators.

1. Strategy Analytics. Data includes digital cameras, MP3 players, media players and portable game consoles.2. talk3g.co.uk quoting a 2010 study by Coda Research Consultancy3. Both Informa and Analysys Mason are in agreement

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Evolving Offload Solutions

Mobile operators are exploring or deploying Wi-Fi offload strategies to meet the increased mobile data demand and relieve network congestion. To assist in that evaluation, 3GPP4 and the Wireless Broadband Alliance5 identify a number of requirements that need to be met for a robust Wi-Fi Offload solution:

• Network Discovery and Selection• Use of existing 3GPP credentials or automation of enrollment for new credentials• Security of network attachment, user credentials and data• QoS (appropriate latency and jitter for different applications)• Charging

Other requirements such as Battery Life Preservation (when out of coverage) also support increased min-utes offloaded to Wi-Fi.

This paper identifies three “phases” of Wi-Fi offload that incrementally build capability into the network in accordance with 3GPP recommendations. It describes the technical elements required in the network and client, the impact on user experience, and the functional benefits provided to the operator. These phases are:

• Phase I: Enabled Mobile Client, tackling the “connect to the network” priorityo We also identify a Phase I Advanced which leverages Advanced client functionality to boost

operator control and improves the user experience• Phase II: Enabled Mobile Edge, enabling the ability to reuse authentication credentials in a secure

and seamless fashion• Phase III: Enabled Mobile Core, enabling a blended wireless access service and adding the

dimensions of quality of service enforcement, subscriber policies, reuse of legacy services such as optimization techniques, charging operators services.

The following chart summarizes the progression of each phase with the corresponding major features. The following sections describe each phase in more detail.

Features I I (Advanced) II III

Network Auto Select √ √ √ √

Access Point Authentication √ √ √

Policy Control √ √ √

Analytics (client-based) √ √ √

Authentication & Authorization √ √

Security √ √

Traffic visibility & end-end analytics √ √

Session persistence √

4. 3GPP TS 23.4025. HotSpot 2.0 Working Group

Table 1: Phases of Wi-Fi Services Deployment

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Phase I: The Enabled Client

The simplest type of “Wi-Fi Offload” is a manual process initiated by the user. The process requires the end user to switch the Wi-Fi radio on or off, scan for available access points, enter (if required) passwords and pin for the radio attachment (e.g. a 10 digit WEP key) and, sometimes, a second logon phase via a web portal username and password. This multi-step process is cumbersome for the user, prone to input errors, and often not compatible with many 3G-based operator services and security protections.

For operators, the advantage of the manual process is that it requires no changes to the network and minimal accommodation on the handset other than the availability of the Wi-Fi radio. The disadvantage is the complete loss of operator visibility to the quality of the user experience and the inability to leverage that mechanism reduce network congestion in critical times of peak capacity. The decision to activate Wi-Fi is totally at the discretion of the subscriber. However, subscribers expect connectivity to remain intact and will typically attribute any service issues to the carrier, regardless of which network is actually the culprit.

Emergence of the Policy-Driven Client

To provide operators with greater control of offload decisions and to streamline the user experience, ven-dors have developed software for devices User Equipment (UE) that can route data traffic based on policies defined by the mobile operators. For example, Smith Micro Software, Inc. provides a UE client as part of its NetWise DirectorTM solution that intelligently connects mobile users to the Internet based on rules defined by the carrier. Enforcement of the policy may be based on events and conditions, such as time-of-day, network technology priority, mobility posture (mobile vs. stationary) and radio signal strength.

The addition of dynamic policy control allows operators to determine flexible offload rules and make more granular decisions on whether, when and how subscribers, devices, and applications should be offloaded to a different network. Mobile operators can identify appropriate policy parameters, and selectively apply and adjust policies to ensure appropriate use of alternative networks.

This approach is a viable solution for network operators with urgent, near-term offload needs. While it pro-vides sophisticated, policy-based offload with no core network investment, it becomes far more powerful with the addition of security, session persistence and integration with legacy application features available in the next two evolutionary phases. The enabled, policy-driven mobile client is a pre-requisit for imple-mentation of Phases Two and Three which deliver a more robust experience for subscribers, and more visibility, control, and revenue opportunity for operators.

Diagram 1: Phase I+ Wi-Fi Service - Carrier Defined Client Offload Policy

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Phase II: Mobile Edge Enabled

As illustrated in Table 1, Phase I Wi-Fi service satisfies the primary objective of offloading the RAN. How-ever, many within the operator ranks have difficulty labeling it an “operator branded service”. Significant components of the “service” that subscribers sign up to are missing: Access to their data services for one, and some expectation of protected (secure) communications for another. Moreover, operators effec-tively hand their subscribers over to Internet properties in this scenario, further eroding customer loyalty and their brand.

The primary driver for the second phase of Wi-Fi offload design is to ensure that end users can continue to have the same access to operator provided content, applications and services through Wi-Fi as they would via 3G. For the operator, the ability to supporting additional carrier revenue elements such as pre-paid charging plans, location-based service and ad insertion service opportunities is also important. Depend-ing on the implementation, however, devices may be challenged accessing both the local LAN and Internet services in parallel without switching off the association with the core network. The Phase II Mobile Edge Enabled Wi-Fi offload solution by Stoke and Smith Micro is shown in Diagram 2.

This Phase adds a 3GPP defined packet data gateway (PDG) that interacts with the enabled mobile client to create a secure tunnel to the required service(s). In addition, routing intelligence is provided within the SSX (PDG) allowing for direct connection to the Internet for non-operator provided services that do not require or benefit from optimization provided by the Operator Services Domain.

In this Phase II architecture, 3GPP requires 3 key elements to be deployed and managed.

1) Enhanced Client Software • As in the first phase, client software on the device or User Equipment (UE) is required to ensure

the device connects to the appropriate network. The Phase II client is enhanced to automate authentication and provide secure connections to the operators’ networks.

• Data encryption (optional) • Integration to a Mobile Data Gateway providing features and interfaces which are flexible in nature

to allow either the reuse of existing legacy services provided by the GGSN (The Tunnel Termina-tion Gateway or TTG feature) or separately implementing these standardized features, where such features need to be enhanced or replaced (The Packet Data Gateway or PDG). The PDG and TTG are described below.

• The Client Software manages the security association with the 3G network and the (Wi-Fi) Mobile Data Gateway and, if enforced, encryption through to the PDG/TTG.

Diagram 2: Phase II Wi-Fi Offload

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2) 3GPP AAA Server• Integration and real-time access to the service provider’s authentication center must be de-

livered on an IP Session. Typically either a standalone AAA server or an AAA server that can access the 3G Home Location Register (HLR) must be deployed and managed. The key features of the AAA are:o IP session admission control and management, including usage enforcement o Subscriber service policy storage/retrievalo Interfaces to HLR

3) Operator Network Edge Component – The Mobile Data Gateway (PDG/TTG)• A Packet Data Gateway (PDG), such as the Stoke Session Exchange (SSX), provides the routing to

and from the Wi-Fi network. The PDG is defined by 3GPP in the specification for WLAN Interwork-ing and delivers a number of important features, namely:o Secure (IPsec) sessions to the mobile deviceo IKEv2 / IPsec from client to PDG allows for automation of the session establishment phaseo Provides usage visibility (CDRs, routed traffic) for charging and services but there is little opera-

tor controlo Allows breakout / offload of specific types of traffic to the Internet, bypassing core components

and thus alleviates some of the data plane usage on GGSNs and Service LAN infrastructure.

• It must be noted that 3GPP defined a PDG variant, the Tunnel Termination Gateway or TTG, that, instead of creating a new source for billing information, policy enforcement and interface to the Gi LAN, the TTG funnels all Wi-Fi attached users through the GGSN. Like the PDG, the TTG per-forms a number of functions, including: o Authentication of Wi-Fi connected users to the security and garden wall of the operator core o Secures subscriber communications (control & data traffic) end-end, given tunnel encryption

from the UEo Application of static subscriber specific policies (QoS, charging triggers/CDRs, bandwidth al-

location, traffic filtering) acquired from AAA or policy serverso Detect services (e.g. SIP/VoIP, URLs) in the traffic stream and apply appropriate policies, includ-

ing routing to the application servers where applicable

The benefits of a TTG-only based solution need to be balanced against a number of draw-backs, including:• Inability to allow breakout to the Internet as the anchoring for all traffic is on the GGSN• Increased end-end latency when connected via Wi-Fi which is added by the GGSN and potentially

Service LAN components• No session mobility, or mobility with long session re-establishment delays

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Whilst the TTG simplifies WLAN interworking implementations, the GGSN is still required to carry all sub-scriber service and Internet bound traffic: as the primary driver is to “offload” traffic via Wi-Fi, routing traffic back into the GGSN represents a major limitation with this approach making it a 3G/Wi-Fi specific solution.

More recent components for the PDG based solution, the PCRF and O/FCS, provide for dynamic policy enforcements and real-time online/offline charging. With this added flexibility, including an enabled mobile client and packet data gateway, operators can set offload policy with very specific rules for network attach-ment over a varying range of Wi-Fi network providers, based upon real-time network conditions. This sets the stage for the third and final phase of Offload capability.

Phase III: Converged Mobile Core – Seamless Services

In Phase II operators gained the visibility, control, and seamless connectivity that subscribers are used to with their cellular attached devices. The third phase solution adds session continuity, offering a seamless wireless connection service using the best available connection at any given time and location. The user experience is transparent and users can move freely between 3G and Wi-Fi connections while keeping applications active and without requiring manual intervention to re-establish connections. Importantly, the use of an Evolved Packet Core’s Packet Data Network Gateway (P-GW) allows for network convergence whereby 3G, Wi-Fi, 4G and other non-3GPP access network types can make use of the same solution for offloading 3GPP cellular networks.

3GPP Release 8 provides for session mobility between the WLAN network and the 3G and/or 4G networks, with the “anchor point” being realized by the P-GW. The Phase III session mobility between the different radio technologies are managed in a similar way to how the SGSN manages users moving between RNCs and the MME/S-GW manages users moving across eNodeBs and the ePDG acts as the local mobility an-chor (LMA) for non-3GPP access networks such as Wi-Fi. Moreover, the subscriber authentication, authori-zation and policies defined for 3GPP access are reused for Wi-Fi (and other access networks).

Diagram 3: Phase II with Tunnel Termination Gateway (TTG)

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The requirements for a successful phase 3 solution include:

• Intelligent software client, or operating system feature, capable of implementing operator policies and selecting the “best” wireless service establishing a “make before break” connection with the mobility anchor

• Subscriber movements between access technology domains is invisible to mobile services and the Internet

• Hand-over is sub-second to preserve multimedia sessions• Secure UE to Core Network communications regardless of access technology

The ePDG solution from Stoke is designed to secure network attachment, authentication and mobility for untrusted non-3GPP access networks such as Wi-Fi. The same features, namely IKE, MIP or GTP, can be configured to implement the required network-side requirements for trusted networks, i.e. Security Associa-tions via IKE from the Wi-Fi network to the P-GW for mobility and secure authentication.

Compelling Solutions Are Required

The Wi-Fi offload end-to-end reference solutions architectures presented in this paper integrates Stoke Wi-Fi eXchangeTM, Smith Micro Software’s NetWise DirectorTM Client, Policy Server and Analytics. Stoke and Smith Micro have partnered to define a prescriptive Wi-Fi offload solution with a comprehensive and jointly tested feature set. The NetWise Director suite delivers the UE client capability required for session continuity allowing users to seamlessly move between networks by making use of the existing 3GPP-based authentication methods (i.e. EAP-SIM/EAP-AKA). Together with the NetWise Director client, Stoke’s PDG/TTG mobile network gateway delivers a world-class Wi-Fi offload solution for mobile operators. The ad-dition of NetWise Director’s Policy Server provides additional flexibility to service providers in managing network and subscriber policies as well as NetWise Director client and policy upgrades.

The key features of the Stoke Wi-Fi eXchange Wi-Fi offload solution with Smith Micro’s NetWise Director client include:

• User authentication and authorization: performed using IKEv2 between the client and the SSX-3000, and using DIAMETER between the SSX-3000 and the AAA server. Both EAP-SIM and EAP-AKA are supported by default.

• Session connection/disconnection: User/client and SSX-initiated connection/disconnection are both supported IKEv2 messages.

• Connect/disconnect a session based on AAA-initiated request (i.e. when a subscriber profile has changed indicating that they have a change to their service options).

Diagram 4: Phase III Wi-Fi Offload – Evolve Packet Core with 3GPP defined Enhanced PDG

Stoke, Stoke Session Exchange, Stoke Wi-Fi eXchange and the Stoke logo are trademarks of Stoke, Inc. NetWise Director is a trademark of Smith Micro Software, Inc. Copyright © 2012 Stoke, Inc. All rights reserved. Lit# 130-0011-003

www.stoke.com10


• Charging Data Function (CDF) capable of generating and forwarding CDRs to the appropriate Charging Gateway Function. The CDR format is compliant to WLAN-CDR parameters listed in TS 32.252 using GTP’ for transfers.

• Support for “In Service Software Upgrades” (ISSU) resulting in zero operational downtime within a single chassis when upgrading system or application software

• Optional Stoke-defined implementation of Lawful Intercept standards and interfaces as an optional capability

• TTG mode of operation, using the Gn’ to interface to an existing GGSN for session continuity as well as reuse of existing functions for charging, Lawful Intercept, etc.

This decision making capacity will be further enhanced by the recent efforts in 3GPP standards development work and software developers on creating the Access Network Discovery and Selection Function (ANDSF), a policy database that informs the client manager what Wi-Fi access points are accessible and how to con-nect. Some implementations will also provide details of the quality of the connection at a given location.

Conclusion

The mobile and wireless industry has embraced Wi-Fi as a de facto, license-free spectrum solution that data services in particular can capitalize on; both from its convenience for indoor wireless mobility as well as its utility as a mechanism to offload traffic from overburdened 3G networks. The key drivers include:

• Low cost and increasing coverage• Ubiquitous support in laptops and smartphones• High capacity and low latency when compared to 3G data

In this document, Stoke and Smith Micro have discussed three phases of Wi-Fi offload that deliver incre-mental benefits to mobile operators and improve the user experience.

• In Phase I, operators can achieve Wi-Fi offload through an Enabled Mobile Client with policy con-trol served by a service provider server. The user experience is enhanced through simplification of the authentication process and access to Wi-Fi networks at times of heavy congestion.

• In Phase II, interworking between the client and a mobile data gateway, is introduced. Session security and automated connectivity are enhanced and the user is able to access more operator services over Wi-Fi than possible in Phase I.

• In Phase III, the addition of session continuity allows users to seamlessly keep applications active when transitioning between 3G and Wi-Fi networks. In Phase III, the highest level of functionality, Wi-Fi utilization and quality of user experience is achieved through a combination of mobile client and network elements that provide basic offload, security, and session persistence.

To learn more about the benefits of Wi-Fi Offload or to request a customer ROI calculation, please contact:

Smith Micro Software, Inc.smithmicro.com

Corporate Headquarters51 ColumbiaAliso Viejo, CA 92656

+1.949.362.5800

Stoke, Inc.stoke.com

Corporate Headquarters5403 Betsy Ross Dr.Santa Clara CA, 95054 USA

+1.408.855.29001.877.786.5348

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!WiFiOffload Evolution 130 0011 003