You may be forgiven for thinking that smartphone data flow is the same regardless of whether it’s sent over Wi-Fi or cellular networks. It isn’t. Smartphones actively discriminate between the two, and that leads to a distortion of traffic quantity and uplink/downlink ratio. We consider the implications.
Why the difference?
Smartphones assume that Wi-Fi is free, on the basis that mostly it’s a convenient replacement for the wired connection in your home or office. We rarely need to “side-load” our smartphones by physically plugging them into the USB ports and running iTunes or equivalent any more. Instead, App updates, podcast downloads and data sync are seamlessly and quietly handled in the background. This has made life much more convenient, with physical connections only required for power charging – something that itself may become outdated if inductive charging using WPC (Wireless Power Consortium) Qi (pronounced Chee) or PMA (Power Matters Alliance) takes off.
For example, Apple mandate that both Wi-Fi and power are connected for iPhone iOS updates, with a workaround using iTunes on a computer. They also enforce a 100Mbyte limit on individual App store downloads to avoid surprise cellular bills. Photos are synchronised with iCloud only when connected through Wi-Fi.
The assumption is that cellular is chargeable and hence a precious resource while any Wi-Fi is free and can be used to its full technical potential.
Side Effects
The data traffic patterns for Wi-Fi differ considerably from cellular. There’s a noticeably higher uplink ratio, driven by synchronising photos and other locally captured data which aren’t sent when on cellular. Traffic demand is higher overall, with Apps downloads and other updates also deferred for Wi-Fi use.
This is noticeable at stadiums and in public areas where capacity is most constrained. Sometimes this degrades the public Wi-Fi service and limits or blocks access for other users.
I had a conversation with one European network operator about whether they could actively block or traffic shape such downloads/uploads to share out available resources more equitably. He questioned whether this would fall foul of network neutrality rules.
Confusing the system
Personal hotspots, sometimes called Mi-Fi, which create a temporary local Wi-Fi access point connected through LTE can confuse the issue. Attached devices think they are connected to Wi-Fi and behave as though it is unlimited.
Laptops rarely make any distinction about this anyway. We occasionally hear of scenarios where the overnight backup or enterprise software update is triggered without realising it’s using an expensive (roaming) cellular connection.
So how should the network take this into account?
When we dream up ever more complex schemes about how the network might determine or select between cellular and Wi-Fi, we need to consider the consequences. In future, there will be other options too:
- Wi-Gig will appear on smartphones during 1H2017, offering Gigabit speeds over a few metres (i.e. within the same room). Ideal for synchronising those photos, video and other extensive data.
- LWA offers to boost cellular capacity by adding Wi-Fi as a supplemental channel when needed and available.
- LTE-U/LAA aim to boost cellular capacity by running supplemental LTE channels in unlicenced bands.
I’d expect Wi-Gig to be handled in a similar way to other Wi-Fi access, and treated as if free and unlimited. Perhaps some apps will be smart enough to make more extensive use of it, predicting and preloading data when connected.
LWA and LAA both present a challenge for billing purposes. I’d expect both will be charged to your cellular account (we discussed this topic in more detail before) and be treated as if connected via cellular alone.
How could smartphones and wireless devices evolve to make best use?
Smartphone Apps generally have three connection states for data:
- Offline
- Wi-Fi
- Cellular
(Yes, it’s true that both Wi-Fi and Cellular can be connected simultaneously, in which case priority is given to Wi-Fi. But let’s ignore that for now.)
One option is to add a further connection state for “chargeable Wi-Fi” which would treat the connection in the same way as for cellular. Alternatively the connection state should evolve to become “chargeable” or “free” rather than be based on technology used.
It may also be useful for Apps to take into account whether roaming into another country or not. This is becoming more confusing, with EU rules bringing in free roaming within Europe, some networks offering free roaming in certain countries and national roaming to rural carriers in the USA. Could the smartphone identify that premium costs apply, encouraging Apps to be more thrifty with their data consumption?
Should “time since last sync” become a factor? Some Apps might decide to sync data over a chargeable connection after a certain period of time, safeguarding your precious holiday snaps towards the end of your vacation. Perhaps operators might sell off spare overnight capacity for this purpose. While we could dream up some innovative schemes, I wonder if this simply becomes too confusing and complex, losing the attraction of instant gratification and interaction that we enjoy today.
So what’s the likely outcome?
Long held assumptions and operational rules take a long time to change in the telecoms industry. This is particularly the case where billing systems are involved – so many parts of the network and software versions have to be upgraded.
Many Apps simply don’t take into account what type of connection they are using and require manual configuration through the operating system to block use. That's particularly awkward when roaming. Confusion reigns. Some long term thought and direction would help.
The passive priority given to Wi-Fi is important for traffic planning. Usage won’t be the same as cellular where both are equally available. This may help explain why Wi-Fi usage is reported to be higher in some environments, with more tech savvy higher traffic users actively seeking it out and exploiting full use of it.
The different treatment also impacts the business case for investment between Wi-Fi and/or cellular. Smartphones treat these two access methods quite differently, exploiting Wi-Fi as if free while being more thrifty with paid cellular use. The return on investment per bit carried should be higher for cellular than Wi-Fi.
