In Japan, most homes use fiber internet (光回線). On paper, these services advertise 1Gbps or even 10Gbps speeds. But in practice, downloads from websites or apps are often much slower. Why does this happen?
Let’s break it down:
1. Shared network capacity
Although a fiber cable physically runs to your home, you don’t have a fully private line all the way to the internet. Most Japanese fiber services use PON (Passive Optical Network) technology, where dozens of homes share the same splitter and uplink to the provider. That means your connection quality changes depending on what other people in your area are doing. When many neighbors are streaming or downloading, your available bandwidth can shrink instantly.
2. Stable speed vs. peak speed
Internet servers don’t simply send data at your line’s maximum. Instead, they try to find the fastest stable rate. Because your available bandwidth is constantly changing, the server often settles on a speed well below your fiber line’s theoretical maximum. That’s why you may rarely see downloads near “1Gbps,” even if your line technically supports it.
3. Congestion control and why downloads look slow
Most of the internet relies on a congestion control algorithm called CUBIC. It gradually increases speed until signs of congestion (like packet loss) appear, then slows down. Some services use newer algorithms (such as BBR) that can make better use of your line.
On top of that, many websites are not optimized for high-throughput delivery. By contrast, speed test sites like minsoku.net or speedtest.net are specifically tuned and located close to you, so they show the raw capability of your connection — while normal sites often don’t.
4. Real-world proof with 88mon
This is where 88mon comes in. 88mon sits in between your connection and the wider internet. It connects to content over a high-quality, uncongested backbone, then delivers the data to you using congestion control tuned for Japanese residential fiber.
The result: 88mon consistently pushes data at the maximum speed your line can handle — no matter what website or service you’re downloading from.
👉 You can see the difference in action here: 88mon Speed Test Results
👉 And you can try it yourself with our test proxy: 88mon Trial