VoWifi Overview

“Wi-Fi” is a trademark of the Wi-Fi Alliance and the brand name for products using WFA programs based on the IEEE 802.11 family of standards.

When I worked in R&D we used to say that patents are like hostages. The advantage is that we can create them ourselves.  In April 2009, 14 technology companies agreed to pay CSIRO (Commonwealth Scientific and Industrial Research Organization in Australia) $250 million for infringements on CSIRO Wi-Fi patents. Hence Australians labeled Wi-Fi as an Australian invention, though this has not been accepted by everyone without objections (especially in US). CSIRO won another $220 million settlement for Wi-Fi patent-infringements in 2012 with global companies in the US required to pay the CSIRO licensing rights estimated to be worth an additional $1 billion in royalties. Guglielmo Marconi or Joseph Fourier would be bambillionaires these days.

In our post the Wi-Fi refers to a WLAN access to ePC, both trusted over S2a interface or untrusted over S2b interface (3GPP TS 23.402). The VoWifi is then a voice and video over Wi-Fi IMS profile, defined in GSMA IR.51. If you are familiar with VoLTE (IR.92 and IR.94), the VoWiFi defines the same set of services, just over a different access network. The service network – the IMS – remains the same. Sure we need to be more sensitive when it comes to muli-device scenarios or access transfer.



This article is focused on the technical aspect of the VoWifi definition. Would you like to know a bit more about why to deploy the VoWifi, check out this post written by Alberto Diez.

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VoLTE Policy Control Summary

In IT and particularly in Telco we are obsessed with abbreviations. My wife always loughs and tries to mimic me when she listens to my calls. Today we should be very careful as many of them start on ‘P’ – PCC, PCRF, PCEF, P-CSCF, PGW, PDN, PDG, PDB, PHB. But no worries, there will be abbreviations starting on other letters as well 🙂

In the IMS we have separated signalling and media data. However a full independence of control and user plane is not desirable. We want to control when the media starts and stops, we want to be sure about media routing, we want to ensure Quality of Service (QoS). And, of course, we want to accordingly charge the users.

In order to achieve these requirements we use two techniques in the VoLTE architecture:

  • Policy and Charging Control (PCC)
  • Differentiated Services (DiffServ)

Policy and Charging Control

PCC functionality comprises of Policy Control (e.g. QoS, media gating, ..) and Flow Based Charging. The ETSI TS 29.212, 29.213, 29.214 and 29.203 define Policy and Charging Control Architecture. There are many PCC functions defined. For us the main 3 PCC elements are:

  • Application Function (AF)
  • Policy Charging and Rules Function (PCRF)
  • Policy Control Enforcement Function (PCEF)
Policy and Charging Control (PCC) Architecture

Policy and Charging Control (PCC) Architecture

Application Function

In VoLTE is the AF incorporated within the Proxy-CSCF. The P-CSCF provides the information related to the control plane signaling. The information is taken from SIP/SDP session setup and it is forwarded to the PCRF via the Rx reference point. Each new SIP message that includes an SDP payload or session events (e.g. session termination, modification) can trigger a new request sent towards the PCRF. This ensures that the PCRF gets the proper information in order to perform reliable PCC.

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