Voice over Wi-Fi (VoWi-Fi) is the use of a IEEE 802.11 based wireless network for the purpose of voice conversations and is often referred to as Voice over wireless LAN. In essence, it is Voice over IP (VoIP) over a Wi-Fi network. We see Wi-Fi Calling as an evolution of VoWiFi allowing it to be truly transparent to the end user. With MNO-branded Wi-Fi Calling, the MNOs have linked the VoIP software directly into the phone’s dialler; users don’t need a separate app. Instead, it can be a default way of placing a call, or if mobile phone signal is lost, it will automatically revert to Wi-Fi. Users have access to their existing phone book, and the third party can receive your call without needing to download a third-party app.
Wi-Fi Calling is useful when you’re in an area with weak cellular coverage. For example, when you’re in rural areas or you’re in a large building with poor reception. With this technology, you can make calls even if you are several stories below ground assuming there is Wi-Fi connectivity.
Wi-Fi Calling offers the user the same phone number and the native dialler of the phone without moving in between applications. Calls can be conducted over any Internet accessible device, including a laptop, PDA or VoWiFi units which look and function like DECT and Smartphones. Because you are adding another technology layer, you will enjoy an improved coverage area for making calls with your smart phones. VoLTE is similar to Wi-Fi Calling in that it also uses IP networks to transmit voice calls and is on offer from all of the UK’s mobile operators. Wi-Fi Calling promises to select the best service across 2G/3G/VoLTE and Wi-Fi wherever you may be and hence provides call continuity and delivers seamless transitioning between networks. A Wi-Fi Calling system offers several benefits to organisations, such as hospitals and warehouses, these include increased mobility and cost savings. For instance, nurses and doctors within a hospital can maintain voice communications at any time at less cost for the business, compared to a cellular service.
The introduction of Wi-Fi Calling presents service providers with an opportunity to add value to their VoLTE launches and solidify their WLAN strategies. By incorporating Wi-Fi Calling into their network infrastructure, service providers can also offload significant video call traffic onto Wi-Fi to preserve capacity for LTE data services. This increases network efficiency and frees up capacity for more revenue generating services. It also gives service providers the opportunity to reduce costs for subscribers, thereby increasing customer loyalty and reducing churn.
Wi-Fi Calling is designed to give a better user experience than the existing third party apps, and is now offered by all four UK mobile network operators. The solutions vary however between operators, and are not provided by many of the virtual operators. The service from the big four operators works seamlessly with the green button once the phone is set up correctly, but users need the right type of phone, bought from the operator, with the right type of contract, older handsets may require the use of add-on applications such as with O2 and Three which require a smartphone app: TU Go and InTouch respectively.
Figure 1: Wi-Fi calling options available by UK mobile operators
Maintaining service continuity and seamless transition between technologies (2G/3G/VoLTE and Wi-Fi) can be challenging as service disruptions could occur because of IP address changes. Where the Wi-Fi network is a carrier grade network this problem is not so much of an issue and disruptions are often in the order of milliseconds and are unnoticeable. The problem is when the Wi-Fi network has little or no relation to the MNO, possible impacts include the failure of call handovers between Wi-Fi Calling and cellular resulting in the need to reinitiate enterprise VPN sessions, and disrupted file downloads.
End users expect consistency in service offerings across any network — whether LTE or Wi-Fi. Generally, network voice and video are not securely accessible from Wi-Fi today. Therefore, content may be susceptible to snooping, and the core network of the service provider could be exposed to public IP access.
Designing Wi-Fi Calling ready networks
Wi-Fi networks can be classified into three main categories, consumer, enterprise and carrier grade.
Figure 2: Wi-Fi calling features and their class of Wi-Fi network
Consumer-grade networks are often deployed in homes by home users to do basic tasks such as access the internet, store photos, and share resources. The equipment (usually a single Wi-Fi router) is usually purchased locally or obtained through an internet service provider. Price and ease-of-use are the most important considerations in consumer-grade equipment, and because of this, features and support are often extremely limited.
Wi-Fi Calling will work with consumer-grade home Wi-Fi networks, provided there are good signal levels and that no one is running the network to its capacity by downloading large files or streaming live videos.
Enterprise grade Wi-Fi networks use enterprise-grade equipment. Compared with consumer-grade equipment, enterprise grade is more flexible, reliable, and customisable. It’s also usually more complex as you may need a certified networking or systems administrator to install and monitor its usage. These networks often have many access points which are centrally controlled via a wireless LAN controller and allow roaming between access points. Depending on the use of the Wi-Fi network, some businesses will also opt for a fully resilient network. The main use of the majority of enterprise Wi-Fi networks is to give employees access to wireless internet, emails, file transfers and conference calling from fixed desks. With this increased usage of smart devices such as smartphones and tablets, mobility is becoming more important, to ensure employees can initiate a Wi-Fi call whilst sitting at their desk and then continue their conversation whilst walking across the floor. End users are often oblivious to the complexities of the technology, they are just interested in good call quality and continuity. The business is often interested in using a technology that can reduce call costs and also ensure end user experience is of high standards. In order to satisfy both criteria, the Wi-Fi Calling ready network design should have the following key considerations built into the design:
- Ensure good Wi-Fi signal levels wherever employees may roam
- Ensure 20% overlap of good signal at cell edges to ensure AP to AP roaming without calls dropping
- A Wi-Fi network that supports voice telephony must be carefully designed in a way that maximises performance and is able to support the applicable call density
- Move voice traffic to a higher QoS queue to ensure voice packets are not impacted when non-realtime applications are loading the network
- Optimise access point association thresholds to ensure connected users achieve the best possible user experience at cell edges
As mentioned earlier, failure of call handovers between Wi-Fi Calling and cellular as the user device leaves the Wi-Fi coverage or building results in the need to reinitiate VPN sessions.
Carrier-grade equipment is used primarily in the telecommunications industry to provide phone and data services for thousands of people and businesses. Carrier networks are mission critical so they need to be carefully designed and tested at every stage to ensure absolute dependability and performance.
The key considerations of designing carrier grade Wi-Fi Calling networks builds on those already in place with very high end enterprise networks but with the additional requirement of facilitating seamless login, roaming between technologies and higher levels of security.
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