Lag During File Transfers: What Bufferbloat Is and Why the Internet "Dies" as Soon as Someone at Home Starts Downloading or Uploading Large Files

It's evening and everyone at home is online. The son is gaming, mum is on a video call with her sister, dad is watching a film. Everything's fine — until the daughter starts uploading video from her phone to the cloud, or Steam begins downloading a 50-gigabyte update. That very second, game ping jumps from 20 to 500 milliseconds, the video call turns into a slideshow and websites open with a delay of several seconds. Yet a speed test may show perfectly decent numbers. It's not a bad provider or a "weak" plan — it's a phenomenon called bufferbloat, and it occurs in almost every home and office. The good news is that it can be eliminated by configuring the equipment properly.

Speed and latency are different things

Internet speed (bandwidth) is how much data can pass per second — like the width of a pipe. Latency is how long it takes one piece of data to reach the server and come back — like the time a drop takes to travel through the pipe. Downloading a film depends on width, but games, calls and opening websites depend on latency. You can have a gigabit plan and still suffer huge latency under load. That's exactly what happens with bufferbloat.

Where bufferbloat comes from

Routers, modems and provider equipment have buffers — queues where packets wait to be sent when the line is busy. Buffers are there to smooth out brief bursts. But in many devices they're far too large. When someone starts a big transfer, it fills the queue to the brim. Packets from a game, a call or a website request join the back of that queue and wait for thousands of transfer packets ahead of them. As a result, latency climbs from tens to hundreds or even thousands of milliseconds. It's especially severe on upload — when you're sending something to the internet — because upload speed is usually lower and the queue fills faster.

Typical symptoms

• Ping in online games shoots up when someone at home downloads files or streams high-quality video.
• Video calls drop during a cloud backup or photo sync.
• Websites "think" for several seconds before loading, then load quickly.
• Problems appear in the evening when everyone is online and vanish at night.
• Stop the transfer and everything instantly returns to normal.

How to measure it

An ordinary speed test shows only bandwidth. To see bufferbloat you need a test that measures latency under load — some services show it separately for download and upload and give a grade. If ping is 15 milliseconds at rest but rises to 300 during the test, you clearly have bufferbloat. Our technician takes these measurements over a wired connection to rule out Wi-Fi, and repeats them at different times.

How it's fixed

• Smart queue management (SQM). Modern algorithms on the router keep the queue short and share the line fairly between flows. Small interactive packets — games, calls, website requests — get through without waiting, even when someone is downloading at full speed. This is the most effective solution.
• Shaping slightly below the plan speed. So that the router manages the queue itself rather than handing it to the provider's overfilled buffer, bandwidth is capped about 5–10% below the real speed. Losing a few percent of speed is barely noticeable, while latency becomes stable.
• QoS and priorities. Prioritising certain devices or traffic types is a useful extra, but without queue management it works poorly.
• A suitable router. Many provider routers and budget models can't manage queues, or can't cope at high speeds. Sometimes the router needs replacing with a model that supports SQM and has a powerful enough processor.

Where Wi-Fi comes in

Wi-Fi has buffers too. If the signal is weak and there are many devices, latency rises even without any transfers. So a good setup includes Wi-Fi as well: the right band and channel, adequate coverage and, for gaming PCs and consoles, a cable. Modern routers with good airtime management can also shrink queues on the wireless network.

What our technician does

1. Measures latency at rest and under download and upload load, over cable and over Wi-Fi.
2. Checks whether your router supports queue management and has enough power for your plan.
3. Sets up SQM, bandwidth shaping and priorities, or selects a suitable router.
4. Tunes the Wi-Fi and connects gaming and work devices by cable where possible.
5. Repeats the measurements under real load and shows you the "before" and "after".

A real example

A family in Gldani — two teenage gamers and parents working from home — complained that the internet was "impossible" in the evenings, despite a 500 Mbit/s plan. The provider visited twice and showed that the speed was fine. Our technician ran a test under load: ping was 12 ms at rest but rose to 900 ms when files were being uploaded to the cloud. The provider's router couldn't manage queues. We installed a router with SQM support, shaped bandwidth slightly below the plan and connected the gaming PC by cable. Now, under full load, ping rises to 20–25 ms at most, and games and calls work alongside any transfers.

Call a technician

If the internet becomes unusable as soon as someone starts downloading or uploading files, we'll come to any district of Tbilisi around the clock and tune your network. Learn more on our internet problems, router setup and network troubleshooting pages.