Every peer-to-peer file transfer has one rule that cloud services don't: the sender must stay online until the recipient finishes. It's the honest trade-off of sending files directly. This guide explains why the rule exists, how long you actually need to stay connected, how to keep Windows, macOS and your browser awake, and what to use instead when you can't.
Why does the sender have to stay online?
Because in P2P file transfer there is no copy anywhere else. With a cloud service, you upload the whole file first; the provider stores it, and the recipient downloads from the provider's servers whenever they like. With StrongFolder, nothing is uploaded in advance. When the recipient opens the link, their browser asks yours for the files, and your browser reads them from your disk and streams them over an encrypted WebRTC connection.
That design is what gives P2P its advantages:
- No upload wait — the recipient starts immediately.
- No stored copy — Files are never uploaded to or stored on a StrongFolder server.
- No size cap from the service — there is no storage to pay for.
The same design is the reason for the rule. If your tab closes, the source disappears. The link works while the sender keeps sharing. When the sender clicks Stop Sharing or closes the tab, the files are no longer available.
What stops a P2P transfer?
| Event | Transfer continues? | What to do |
|---|---|---|
| You switch to another tab or app (computer) | Normally yes | Keep the StrongFolder tab open |
| You close the StrongFolder tab or the browser | No | Wait until the recipient finishes |
| You click Stop Sharing | No | Only when everyone has the files |
| Computer goes to sleep or hibernates | No | Turn off sleep for the session |
| Laptop lid closed on battery | No (it sleeps) | Plug in; change lid action or keep it open |
| Wi-Fi drops or you change networks | No | Use a stable connection; cable if possible |
| Browser discards the tab to save memory | No | Add the site to the "always active" list |
| Phone screen locks or browser goes to background | Often paused | Keep the page on screen while sending |
The same applies on the recipient's side: if their computer sleeps, they stop receiving. Tell them to stay online too.
How long do I need to stay online?
The transfer can't be faster than your upload speed (or the recipient's download, whichever is slower). Best-case times for one recipient:
| Size | 20 Mbit/s upload | 50 Mbit/s upload | 100 Mbit/s upload | 500 Mbit/s upload |
|---|---|---|---|---|
| 5 GB | ~33 min | ~13 min | ~7 min | ~1.3 min |
| 20 GB | ~2.2 h | ~53 min | ~27 min | ~5 min |
| 50 GB | ~5.6 h | ~2.2 h | ~67 min | ~13 min |
| 100 GB | ~11 h | ~4.4 h | ~2.2 h | ~27 min |
| 500 GB | ~2.3 days | ~22 h | ~11 h | ~2.2 h |
Real transfers run somewhat slower than these figures because of protocol overhead, disk speed and, on restrictive networks, a relay hop. One link can be opened by several recipients; each downloads directly from the sender. If three people download at the same time, they share your upload, so each gets about a third of it.
To find your upload speed, run any internet speed test and look at the upload number — on many home connections it is far lower than the download number.
How do I keep Windows awake during a transfer?
- Plug in the laptop. Battery-saving modes are more aggressive about sleep.
- Open Settings → System → Power & battery → Screen and sleep (on recent Windows 11 builds, Screen, sleep & hibernate timeouts; on Windows 10, Settings → System → Power & sleep) and set sleep when plugged in to Never for the duration.
- If you will close the lid, set Control Panel → Power Options → Choose what closing the lid does → When plugged in: Do nothing. Undo it afterwards.
- Turning the screen off is fine — only sleep stops the transfer.
- Optional: Microsoft's free PowerToys includes Awake, a tray tool that keeps the PC awake for a set time without changing your power plan.
How do I keep a Mac awake during a transfer?
- Plug in the MacBook.
- Open System Settings → Battery → Options and turn on Prevent automatic sleeping on power adapter when the display is off. On a desktop Mac, look under Energy (Energy Saver). Menu names vary slightly between macOS versions.
- Or open Terminal and run
caffeinate -i— the Mac won't idle-sleep until you press Ctrl+C. It's built into macOS. - Don't close the lid unless the MacBook is connected to power and an external display; otherwise it sleeps.
How do I keep the browser tab active?
- Don't close the tab and don't quit the browser until the recipient finishes.
- Chrome: Settings → Performance → Always keep these sites active → Add →
strongfolder.com. This stops Memory Saver from deactivating the tab. - Edge: in the performance settings, add the site to the list of sites that should never be put to sleep (sleeping tabs).
- Phones: keep the page on screen and the phone unlocked; mobile browsers pause pages that go to the background. For long sends, use a computer. See PC to phone file transfer.
- Avoid other big uploads at the same time: cloud backup, photo sync and video calls compete for the same upload bandwidth.
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How can I plan a long transfer?
- Agree on a time window with the recipient — both computers awake, both online.
- Start before you leave your desk, not as you walk out: the first minutes show whether the connection is direct and how fast it runs.
- Use a cable for the sender if possible; Wi-Fi is fine but less stable over hours.
- Split very large sends into a few folders. If the connection drops, you only redo one batch.
- Check the recipient's free disk space first. No size limit set by StrongFolder. The practical limits are free disk space on the recipient's device, connection speed, and how long both devices stay online.
- Send overnight from a desktop that stays on anyway, if your upload is slow.
What can I use when I can't stay online?
P2P is the wrong tool when staying online is impossible. Good alternatives:
| Situation | Better option | Why |
|---|---|---|
| You leave in 10 minutes; file is a few GB | Transfer service (WeTransfer-type) | Upload once, recipient downloads later |
| Recipient downloads tomorrow, other time zone | Cloud drive link | Copy waits on the server |
| Many people need it for weeks | Cloud drive (Google Drive, OneDrive, Dropbox) | Shared access, previews |
| Sensitive files that must stay available | End-to-end encrypted cloud | Stored copy the provider can't read |
| Terabytes, slow upload, same city | External drive | Faster than any upload |
| Always-on machine available (office PC, NAS) | Send from that machine | It stays online for you |
For a fuller comparison see P2P vs cloud file transfer and WeTransfer alternatives.
Summary
The sender stays online because, in P2P, the sender's device is the only copy. That's the price of no upload, no stored copy and no size cap from the service. Estimate the time from your upload speed, keep the computer awake and plugged in, keep the tab active — and choose a cloud link when you can't. More on practical limits on Limits & requirements.