- Why speed changes with the time of day: rented capacity and crowding
- How to tell congestion apart from other causes
- Busy-hour habits, and what to check before you sign up
The short answer
In Japan, low-cost SIMs are usually offered by MVNOs, companies that rent network capacity from the major carriers (MNOs). They can slow down at lunchtime or during the commute because the capacity an MVNO rents is limited, and many of its users go online at the same moment. Japan's Ministry of Internal Affairs and Communications (MIC) also notes that data speeds may drop when networks are busy, such as at lunchtime, during commuting hours and at night. How much and when depends on the provider, the period and the place, so this article gives no speed figures.
How it works: providers rent width
In MIC's White Paper on Information and Communications, the data access charges MVNOs pay the major carriers are shown per 10Mbps per month. In other words, an MVNO decides how much width, or bandwidth, to rent and pays for it.
Imagine a fictional MVNO whose users mostly open videos and social media right after noon. The rented width stays the same, so each person gets a smaller share and speeds fall. At quieter times, the same width is shared by fewer people, so it tends to feel faster.
MIC's page on service quality measurement also refers to mobile internet services as "maximum speed (best effort)" services, and notes that complaints had grown about advertised speeds differing from real ones. Best effort means the provider aims for the maximum speed but does not guarantee it. The top speed in an advertisement is not the speed you always get.
Speeds are "best effort", not guaranteed. When it is slow, separate place, device and time of day.
Is it really congestion?
Do not blame congestion straight away when things are slow. Check in this order:
- Have you used up your monthly allowance? Speeds may be throttled after that
- In the same place, is it fast at a quiet time, for example a weekday morning?
- At the same time, is it slow in other places too? Signal can be weak deep inside buildings or underground
- Does the same app work normally on Wi-Fi?
If it is slow only at certain times and moving does not help, congestion is the likely cause. If you have no signal or cannot connect at all, suspect something other than congestion.
Habits for busy hours
- Download videos and music on Wi-Fi in advance
- Schedule app and system updates and photo backups outside busy hours
- Check whether your workplace or the places you visit at lunch have Wi-Fi you are allowed to use
- Set a lower video quality for mobile data in your video apps
What you can check before and after signing up
MIC suggests that people concerned about speed check whether a provider measures and publishes its speeds under MIC's guideline, as some do. If a provider publishes results, look at the conditions too, such as the times and places measured. The figures come from measurements under set conditions and do not promise the speed you will get where you are.
If the service turns out different from what you expected, MIC's portal explains the initial contract cancellation system, which lets you cancel within eight days of receiving the contract documents. Some companies use an alternative system called confirmation measures instead. Device purchases often cannot be cancelled, among other caveats, so check your provider's information and MIC's page for details.
Checklist
- Have you ruled out throttling from using up your allowance?
- Is it slow only at certain times of day?
- Is it still slow when you move somewhere else?
- Does it work normally on Wi-Fi?
- Does your provider, or the one you are considering, publish speed measurements?
One thing to check today
Make a note of the times and places where your connection feels slow, for example weekday lunchtime at the station.