From February 28th to March 2nd, Tessares is exhibiting at MWC’22 in Barcelona. We are demonstrating Wi-Fi Cellular Convergence using our Seamless Handover solution sharing learnings from successful trials in the US and Europe.

There was an assumption that the Covid pandemic would slow the growth of mobile broadband usage but this was not the case. During the past year, mobile data is still growing but ARPU has decreased for many markets. Operators are deploying 5G to increase capacity but it will be difficult for them to increase their prices to cover this cost.¹

Fig. 1 – Majority of markets seeing negative ARPU year on year

Many MNOs and MVNOs are also fixed network operators with millions of subscribers using Wi-Fi at home and at public hotspots. Initiatives like OpenRoaming make it easier for subscribers to access these Wi-Fi hotspots. Most end users do not know or care about which network they use, especially if they have unlimited data plans. It makes sense for operators to use the least cost network.

 GSMA ZTC Task Force

This year’s demo was produced in cooperation with the GSMA Zero Touch Connectivity (ZTC) Task Force which includes operator partners such as BT, Deutsche Telekom, Telefónica, Vodafone and Orange. To accomplish this we ported the off-tree implementation of MPTCP to Linux kernel 5.4 used by the Xiaomi Mi1 1 running Android 12. Xiaomi is a strategic partner in the ZTC initiative.

The task force is currently focused on Multipath Connectivity with 5G ATSSS. The goal is to provide end customers with a worry free connectivity experience. ATSSS introduced in 3GPP Rel. 16 uses MPTCP as the underlying technology to allow the steering, switching and splitting of network traffic.   

The GSMA is encouraging operators to support working group activity to further develop the ATSSS standard and to drive ecosystem implementation with infrastructure, device and chipset vendors.

The goals of the project are:

1. Customers should enjoy a positive UX without worrying about the underlying network technology
2. Ensure quality and security even when connected to 3rd party Wi-Fi
3. Encourage flat-rate customers to leave Wi-Fi switched on to reduce cellular network load while increasing customer satisfaction

Demonstrating Wi-Fi Cellular Convergence

Fig. 2 – Experimental setup schema

For this year’s demonstration we measured handover performance for a file download over TCP.  The smartphone was initially connected to a 5G network and a download was started. The user moves into an area where Wi-Fi is available and the download continues over Wi-Fi.  We can control the preference for Wi-Fi using a 0-RTT Converter hosted in the public cloud.

Fig. 3 – A download over a 5G connection is offloaded to Wi-Fi without interrupting the download.

Notice that the handover above is overlapping. Without Tessares’s ATSSS solution, the connection would have been lost and data sent over the cellular network would have had to be retransmitted over Wi-Fi. 

High Quality Video Streaming

In the second scenario a 10 Mbps Wi-Fi connection is not sufficient to carry a 4K 60 fps video stream. The data that cannot be carried over Wi-Fi is carried over the 5G network. This enables the video to be streamed at a higher resolution without any interruptions. When we  leave the area of Wi-Fi coverage, the session continues over 5G. When Wi-Fi is available, the Wi-Fi network can carry the traffic, overflowing to 5G only as necessary. This reduces 5G usage while providing a level of user experience that would not have been possible on Wi-Fi alone.

Fig. 4 – 4K, 60fps video streaming where Wi-Fi is not good enough. Instead of switching off the Wi-Fi, some of the traffic is carried over 5G. If the user leaves the Wi-Fi area, the video continues uninterrupted.

About The Technology

Multipath TCP (MPTCP) is an extension of TCP which allows one TCP connection to be conveyed over several paths, even over different physical networks.

The 0-RTT Transport Converter allows client devices to use TCP extensions like MPTCP that are not supported by web servers or applications. This allows MPTCP to use multiple access networks without making changes to applications or servers. The MPTCP connections are terminated by the 0-RTT proxy on a Hybrid Access Gateway located between the server and the smartphone where the networks converge.

On creating the connection, the client immediately sends a 0-RTT Convert message to the specified IP address and port of the 0-RTT converter. To minimise the latency, 0-RTT Convert protocol uses TCP Fast Open to exchange the address and port of the remote server during the connection’s handshake.

Standards Based Solution

Cellular network operators can deploy 0-RTT Converter servers in their backbone where their networks converge. In the long run, these deployments will migrate to 3GPP ATSSS in the 5G core. Tessares’ “over-the-core” ATSSS solution allows operators to achieve Wi-Fi Cellular convergence today without waiting to upgrade to a 5G core.

Conclusion

Our standards based solution allows a smartphone to seamlessly move between networks for true Wi-Fi Cellular Convergence without negatively impacting the customer experience. Cellular network operators with fixed network assets can take advantage of this solution without having to wait for an upgrade to a 5G core and with 4G also being supported.

Learn more about how we modified a Smartphone to use MPTCP and 0-RTT

This work is supported by NGI POINTER (NGI Program for Open Internet Renovation) which has received funding from the European Commission, as part of the Horizon 2020 Research and Innovation Programme, under Grant Agreement Nº871528.

¹https://tefficient.com/wp-content/uploads/2022/01/tefficient-industry-analysis-3-2021-mobile-data-usage-and-revenue-1H-2021-per-country-16-Dec-update-27-Jan.pdf