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Take full advantage of LTE with VoWi-Fi


Voice over Wi-Fi® (VoWi-Fi) is one way mobile network operators (MNOs) can take advantage of the rapidly growing, highly competitive Wi-Fi market to complement their robust VoLTE service. By leveraging their LTE network strategically, MNOs can not only generate increased revenue for themselves, but provide a superior user experience for their subscribers.

New mobile network architectural models makes VoWi-Fi both attractive and feasible. We’ll briefly describe the benefits, challenges, architecture, implementation, and opportunities in this blog.

Benefits of VoWi-Fi for MNO subscribers

  • Seamless – Unrestricted connectivity and mobility between Wi-Fi and cellular IP networks enables new VoLTE services to be used anywhere, even outside of LTE coverage
  • Simple – Easy to use and connect with automatic network discovery and authentication
  • Secure – Strong network security from a trusted operator that protects data from unlawful intercept and hacking
  • Savings – Voice and video calling everywhere with service bundles that can lower rates and reduce roaming fees

Benefits of VoWi-Fi for MNOs

  • Increased coverage and capacity – MNOs and MVNOs can address LTE coverage gaps with Wi-Fi hotspots, using any open Wi-Fi, or selectively using closed Wi-Fi that they or their partners provide.
  • Optimized network access – Roaming and bandwidth-intensive video traffic can be reduced by offloading it from the cellular network to Wi-Fi.
  • Ability to extend services easily to Wi-Fi – Subscriber’s wireless access can be managed holistically across multiple services

Challenges of adding Wi-Fi to LTE networks

There are 2 main challenges:

  • Service continuity – Mobile device IP addresses must be preserved when moving between LTE and Wi-Fi, to ensure seamless handovers of calls and other network services such as enterprise VPNs.
  • Service consistency/security – Public Wi-Fi networks are susceptible to hacking. Secure tunneling protocols and subscriber authentication methods are required.

Fortunately, these challenges are addressed with the new mobile network architecture that combines Wi Fi/cellular access with new Evolved Packet Core (EPC) functions.  The architecture is described in 3GPP Technical Specification 23.402 (Architecture Enhancements for non-3GPP Services).

EPC architecture for LTE with Wi-Fi access

In the standards, Wi-Fi is considered a type of non-3GPP wireless access, which the MNO can view as either a trusted or untrusted network. To support these 2 network access types, 2 core network functions are needed:

  • Evolved Packet Data Gateway (ePDG) - Supports the untrusted non-3GPP Wi-Fi access network
  • Trusted Wireless Access Gateway (TWAG) - Supports the trusted non-3GPP Wi-Fi access network

For simplicity, we focus in this blog on the ePDG, but both methods perform similar functions for their respective access networks:

  • Secure tunneling and aggregation of traffic from Wi-Fi access points (APs)
  • Interface to the AAA server for authentication of the mobile device to the EPC
  • Access to the EPC via secure tunneling mechanisms to the MNO’s packet gateway (PGW) which provides the IP address for the mobile device
  • Create the session request for bearer establishment and do the VoWi-Fi call data forwarding between the Wi-Fi access network and MNO’s PGW

Although VoWi-Fi is the primary focus here, the method is transparent to the services (including Internet, enterprise VPNs, and IMS).  Indeed, this is the beauty of the solution.

Implementation is relatively lightweight: an ePDG is added to the network and a slight update is made to the device’s client. In return, the solution works for any Wi-Fi AP (because no integration is required) and for any service (such as IMS, enterprise VPN, and content delivery networks).  The TWAG is similar, except it doesn’t require an update to the device, but does require integration with the Wi-Fi AP.

VoWi-Fi: Part of the new IP communications customer experience

When the Wi-Fi/cellular access is used with a virtualized IMS that comes equipped with native APIs, MNOs can deliver new services to their consumers and enterprises.  These include:

  • Video-call offload.  Video calls consume approximately 400 Megabytes/hour, which can cause pricing reluctance in some subscribers.  Yet video brings a new human dynamic to communications, with visual cues and warmth. It can be used creatively, with ambient video, uni-casting, app-embedded video snippets, and so on.  By enabling subscribers to easily choose LTE or Wi-Fi prior to or during the call, the MNO encourages subscribers to experiment with video.
  • Increased coverage.  VoLTE has better audio and newer features than 3G circuit voice.  No longer constrained to the limitations imposed by the 2G/3G HLR/VLR voice roaming architecture, the MNO is free to rapidly create and deploy new features.  However, the MNO might not have complete LTE coverage, or it might be using a very high LTE frequency that has line-of-sight characteristics.  Using VoWi-Fi to fill in coverage gaps, the MNO ensures the new VoLTE service works anywhere.
  • Multi-device.  The new mobile architecture enables tablets and laptops equipped with only Wi-Fi to attach to the MNO’s network and use its services.  Subscribers can choose the most convenient device.  For example, they can answer an incoming call on their tablet, when their smartphone is not within reach.  Multi-device services are particularly interesting, as they can move the call interaction from today’s mode of calling a phone number (which is associated with one device) to calling a person (who can choose to answer the call on whichever device they prefer).
  • Roaming.  Subscribers can easily stay in touch when traveling, using voice and IP messaging (which interworks with SMS texting).  They can continue to use their home network services even while not connected to the service provider’s access network, and reduce the spending that normally occurs while roaming.

Witness seamless VoWi-Fi / VoLTE services at MWC

The new conversation experience is becoming a commercial reality: visit our booth (Hall #3, booth 3K10) at Mobile World Congress 2015 for a live demonstration of VoWi-Fi and VoLTE.  You will see it in action on an Apple® iPhone 6, and implemented on an Android by D2 Technologies and InterDigital Technologies, over our vEPC/ePDG and vIMS network.

Related Material

Alcatel-Lucent IP Mobile Core webpage

To contact the authors or request additional information, please send an email to

David Nowoswiat

About David Nowoswiat

Dave is a senior product marketing manager at Nokia with over 25 years of telecom and industry experience. Lately he’s been doing his part to help manufacturers in their digital transformation journey. In his spare time Dave plays sports, runs the odd marathon and enjoys good craft beer - not necessarily in that order. Reach Dave at David Nowoswiat | LinkedIn | David Nowoswiat | Google+

Edmund Elkin

About Edmund Elkin

Ed’s passion is market development, which for him these days means the 5G core. Based in Naperville, Illinois, he is enthused about what’s next for telecom that helps improve people’s lives and their societies. Previous experiences include AT&T and the US Navy. He holds Bachelor and Master degrees in Electrical Engineering.

Tweet me at @EdElkin1

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