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Teams and Microsoft 365 in China: Why Calls Drop and What Helps

Teams and Microsoft 365 work in China but cross congested international links. What Microsoft advises, the 21Vianet option, and the fixes that help calls.

Updated October 2026.

The short answer

Global Microsoft 365 and Teams are not blocked in mainland China, but their traffic crosses busy international links, so calls freeze and files sync slowly, worst in the evening. Microsoft's own advice is to carry that traffic out of China on a steadier path. A router that covers every device, wired meeting rooms and a low-delay route help most.

Table of contents

Does Microsoft 365 work in China?

Yes, with a catch. There are two different Microsoft 365 services, and it matters which one your company uses.

Global Microsoft 365 is the version most international companies sign up for: the same Outlook, Teams, OneDrive and SharePoint your colleagues use in London or New York. It is reachable from China. When we checked GreatFire's test results on 23 October 2026, teams.microsoft.com connected normally from mainland China, while personal OneDrive (onedrive.live.com) failed every recent test.

The problem is the route. Microsoft's own China guidance says the country's connections to the global internet "go through perimeter devices that are prone to high-levels of cross-border network congestion," and that this "creates packet loss and latency for all Internet traffic going into and out of China" (Microsoft Learn, updated August 2026).

Microsoft 365 operated by 21Vianet is a separate service for China. Microsoft licenses its technology to 21Vianet, which runs the service from data centres in China and handles subscriptions, billing and support. Microsoft says it "does not operate the service itself," that the services "are subject to Chinese laws," and that some features "have not yet been enabled" (Microsoft Learn). Teams operated by 21Vianet is "a physically separated instance service located in China," and Microsoft's feature table lists Live Events and town halls, Voice and third-party apps as not available (Microsoft Learn).

If your company's Microsoft accounts were set up outside China, you are on global Microsoft 365. The rest of this guide is about that case.

What Microsoft recommends for offices in China

Microsoft's China page gives companies with a global tenant clear, practical advice. In plain words:

  • Keep Microsoft 365 off the public internet in China if you can. Microsoft suggests using a private network to carry Microsoft 365 traffic from the China office to a location outside China, then onto the internet there. "Almost any location outside China will provide a clear benefit," it says, and it names Hong Kong, Singapore, Japan and South Korea as examples with low-latency links to Microsoft's network.
  • Use the desktop apps. Outlook, Teams and OneDrive keep local copies, and Microsoft says client caching "can dramatically reduce the impact of network congestion and latency." Browser versions suffer more.
  • Keep dial-in as a backup. If your company has Teams Audio Conferencing, people can join a meeting by phone.
  • Check the rules. For any private network, Microsoft says "you should always consult regulatory requirements."

Microsoft also says it has partnered with telecommunications providers to carry Teams call audio and video on "a higher-quality, preferential network path" between ordinary Chinese internet connections and its global cloud, with "a more than ten-fold improvement in packet loss." Two limits matter. Chat, files and the rest of Microsoft 365 "won't directly benefit," and the improvement does not cover attending large Live Events or town hall broadcasts. Microsoft is explicit that it "has no recommendations on the use of SDWAN or VPN solutions."

China's rules separate approved cross-border connections, which registered companies buy through licensed carriers, from other VPN tools, which sit in a gray area. Our guide Are VPNs legal in China? explains what that means in practice, and our office internet guide compares leased lines with other options. This is general information, not legal advice.

Why Teams calls drop when the speed test looks fine

A video call needs very little speed. Microsoft's recommended figure for a one-to-one Teams video call is 1.5 Mbps each way, and 2.5 Mbps up and 4 Mbps down for a meeting (Microsoft Learn). Almost any office line in China has that.

What a call needs is a steady path. Three things break it:

  • Delay (latency): how long each piece of sound or picture takes to arrive. Long delays make people talk over each other.
  • Jitter: delay that keeps changing. The app has to wait for late pieces, so voices sound robotic and video stutters.
  • Lost packets: pieces that never arrive. A call cannot pause to fetch them again, so words drop out and the picture freezes.

Microsoft's own targets for Teams, measured from your computer to Microsoft's network, are a round trip under 100 ms, packet loss under 1% and jitter under 30 ms (Microsoft Learn training). A congested cross-border link in the evening can miss all three while a speed test still shows a big number.

Microsoft also points at Wi-Fi. Its Teams network guide says Wi-Fi networks "aren't necessarily designed or configured to support real-time media," and that the 5 GHz band is better suited to calls than 2.4 GHz. So "Teams keeps dropping" in a China office usually has two parts: the route out of China, and the last few metres of Wi-Fi.

What helps Teams and Microsoft 365 in a China office

1. Put the whole office on one router. A Throughwire router sits behind your existing internet line and covers every device on its Wi-Fi or cables: laptops, phones, meeting-room PCs, conference speakers and visitors. Nothing needs an app, and nobody has to remember to switch anything on. Our office router guide walks through setup.

2. Choose the route that suits your calls. Our standard route, High Speed, leaves China through Los Angeles and suits most offices. Ultra leaves through Osaka (Japan) or Singapore, both in places Microsoft itself names as good exit points, and is built for low delay. From Shanghai, our app shows typical round trips of about 90 ms to Los Angeles, about 30 to 55 ms to Osaka and about 65 to 95 ms to Singapore, so Osaka is the low-delay choice for eastern China. We have not published measured latency yet, so treat those as typical figures, not promises. Ultra counts at 2.5 times the data (10 GB on Ultra uses 25 GB), so it fits teams that live on calls, interpreted meetings or remote desktops.

3. Wire the meeting rooms. Run a network cable to the meeting-room PC or Teams Rooms device. For laptops on Wi-Fi, join the 5 GHz network and keep the router somewhere open and central.

4. Keep big syncs out of meeting hours. OneDrive can cap its upload and download rates, and its "Adjust automatically" upload option uses only spare bandwidth (Microsoft Support). A large sync on the same line can be enough to make a call stutter.

5. Plan town halls. Microsoft suggests planning about 2 Mbps per viewer for a live-streamed town hall (3 Mbps for 1080p). By our arithmetic, 20 colleagues each watching a one-hour broadcast on their own laptop use about 18 GB of data. One screen in a meeting room uses about 1 GB.

6. Test at the time you actually meet. Make a 10-minute test call at 8 pm on a weekday, when international links are busiest. In our network data for the 30 days to 19 October 2026, everyday working speed on High Speed during China's evening peak (19:00 to 23:59) held at 98% of the level for the rest of the day, though the biggest bursts were lower. Our guide to evening video calls explains what that does and doesn't tell you about calls.

Which Microsoft apps work from China, and how they are routed

On a Throughwire router, and in our apps, Microsoft 365 and Teams go through Throughwire. Microsoft's China-specific services, including Microsoft 365 operated by 21Vianet, and Windows' own connection checks stay on your normal China line and use none of your Throughwire data. You can look up any service in our routing directory.

Microsoft serviceFrom China without helpOn a Throughwire routerTip
Teams calls and meetingsWorks; quality depends on the route and the time of dayThrough ThroughwireCable in meeting rooms; Ultra for call-heavy teams
Teams chat and filesWorks, often slow when links are busyThrough ThroughwireUse the desktop app
Outlook and Exchange OnlineWorks, slow to sync at busy timesThrough ThroughwireDesktop Outlook keeps a local copy
OneDrive for work and SharePointWorks; large files can be slowThrough ThroughwireCap sync rates during calls
Personal OneDriveFailed every recent GreatFire testThrough ThroughwireCounts towards your data
Word, Excel and PowerPointDesktop apps work offline; saving depends on OneDriveSign-in and saving through Throughwire; some install and update downloads come from servers in China and stay localUse the desktop apps, not browser tabs
Microsoft 365 operated by 21VianetSeparate service hosted in ChinaStays on your local lineNo Throughwire data used
SkypeRetired on 5 May 2025Not applicableMicrosoft points Skype users to Teams Free, which goes through Throughwire

When Throughwire isn't the right choice

  • Your company already runs a private cross-border network. That is Microsoft's recommended setup for Microsoft 365. Use it.
  • Your data has to stay in China, or most of your collaborators are in China. Microsoft 365 operated by 21Vianet, or a Chinese suite such as DingTalk or WeCom, may suit you better. DingTalk and WeCom stay on the local line on our router.
  • You only make Teams calls, and they are already clear. Microsoft's telecom partnership may already be doing the job for call audio and video. Test at 8 pm on a weekday before you change anything.
  • You need a contract that guarantees performance. We don't guarantee speed or uptime. A cross-border leased line from a licensed carrier is the formal option.
  • Your connection is a foreign eSIM or a Hong Kong network. Those connections route through Hong Kong and are slower with any service. A China Telecom, China Mobile or China Unicom line works best.

Common questions

Is Microsoft Teams blocked in China?

No. Global Teams is reachable from mainland China, and GreatFire's recent tests of teams.microsoft.com connected normally (checked 23 October 2026). Calls suffer from congestion on international links, especially in the evening.

Why is Outlook so slow in China?

Outlook talks to Microsoft's servers outside China across busy international links. Use desktop Outlook, which keeps a local copy of your mailbox, and give the office a steadier route out of China.

Should we switch to Microsoft 365 operated by 21Vianet?

Only if keeping data in China matters more than working in the same system as colleagues abroad. It is a separate service run by 21Vianet, with its own subscriptions and some features missing. Microsoft documents chats, calls and meetings between 21Vianet Teams and global Teams, but the two remain separate organisations.

Is Ultra worth it for Teams?

For most offices, High Speed is enough. Ultra suits teams on calls most of the day, interpreted meetings, or staff using remote desktops, where lower delay is noticeable. It counts 2.5 times the data, so check your allowance.

How much data does a Teams call use?

At Microsoft's recommended 1.5 Mbps each way for one-to-one video, an hour comes to about 1.35 GB by our arithmetic. An audio-only call at Microsoft's recommended 58 kbps each way uses about 50 MB an hour. On Ultra, both count 2.5 times.

Do Teams Rooms devices and conference phones work with Throughwire?

Yes, if they connect to the router's network by cable or Wi-Fi. They need no app, because the router handles the routing for every device on its network.

Details for your IT team

  • Routing (catalog version 2026.10): microsoft.com, office.com, office365.com, office.net, microsoftonline.com, sharepoint.com, live.com, skype.com and cloud.microsoft go through Throughwire. China-specific Microsoft domains (for example microsoftonline.cn, partner.outlook.cn and chinacloudapi.cn), Windows connectivity checks (msftconnecttest.com) and some China-served download hosts (officecdn.microsoft.com, download.windowsupdate.com, statics.teams.cdn.office.net) go direct. Teams media IP ranges are not mainland allocations, so they use the tunnel.
  • Transport: the router runs sing-box on GL.iNet or OpenWrt and connects with VLESS-REALITY. UDP from apps, including Teams media, is carried inside the tunnel to the exit. QUIC (HTTP/3) to international sites is blocked on the router, so browsers fall back to HTTPS over TCP.
  • Routes: the Los Angeles route uses China Telecom's premium CN2 GIA route. Ultra exits in Osaka or Singapore.
  • Conditional access: if you limit Microsoft 365 sign-ins to known IP addresses, the dedicated IP add-on ($9 a month) gives your office its own static address.
  • Zero-Trust Relay: you can run your own WireGuard, Tailscale, SSH or Cloudflare Tunnel inside Throughwire; we carry it without access to its private contents.