The connection can not be established. What can I do?

Threema calls impress with crystal-clear voice quality and brilliant video quality. Since they are end-to-end encrypted, they are tap-proof. Instead of a phone number, the Threema ID serves as unique identifier.

• The call connection is established using Threema messages in the background; therefore, voice calls are just as trustworthy as chats, and the same verification levels apply
  
• If possible, a direct connection between caller and callee is established (peer to peer) after the connection buildup*
  
• Calls with verification level 1 (red) IDs are routed through the Threema server in order to obscure the IP address (in “Settings > Secure calls” (Android) or “Settings > Threema Calls” (iOS), there’s an option to route all calls through the Threema server)*
  
• Because a constant bit rate is used for audio encoding, no conclusions about the content can be drawn from the size of the transmitted data packets*
  
• Video transmission is an option of Threema calls that can be enabled at any time during an ongoing call. Once a Threema call is established, both parties can independently enable and disable video transmission by tapping the camera icon.
• Thanks to Threema’s contact verification, Man-in-the-Middle attacks can be effectively prevented, and there’s no need to manually verify a code for the purpose of authentication

*) Only applies to 1:1 calls, not to group calls.

For detailed technical information in regard to Threema calls’ security, please refer to the Cryptography Whitepaper.

1:1 calls

The following system requirements must be met by both the caller’s and the callee’s device:

• Android
  • Voice calls: Threema 4.8 for Android or above on Android 5.0 or above
  • Video calls: Threema 4.8 for Android or above on Android 5.0 or above
  • To receive calls when Threema is in the background, Google Play Services are required
• iOS
• iPhone: Threema 3.0 for iOS or above (voice calls) or Threema 4.6 for iOS or above (video calls) on an iPhone 5s or above running on iOS 10 or above
• iPad: Threema 3.0 for iOS or above (voice calls) or Threema 4.6 for iOS or above (video calls) on an iPad Pro, an iPad Air, a 5th-generation iPad or above, or a 2nd-generation iPad Mini 2 or above running on iOS 10 or above
• iPod touch: Threema 3.0 for iOS or above (voice calls) or Threema 4.6 for iOS or above (video calls) on a 6th-generation iPod touch or later running on iOS 10 or above

Group calls require Threema 5.0 for Android or above or Threema 5.6 for iOS or above.

Establish a Voice Call

Select the desired contact in your contact list and tap the phone icon in the title bar (Android), or tap “Call” (iOS). Alternatively, tap the phone icon in a chat’s title bar.

Enable Video

Video transmission can be enabled at any time during an ongoing call. Once a Threema call is established, both parties can independently enable and disable video transmission by tapping the camera icon. This is to say that it’s possible to conduct one-way video calls.

Please note that the system requirements must be met by both the caller’s and the callee’s device in order to make voice or video calls.

Group calls in Threema are end-to-end encrypted and currently available for up to 16 participants. An invitation URL is not necessary; the group members chat can decide whether to join a call or not.

• To start a group call, tap on the camera icon (Android) or the phone icon (iOS) in the top right corner of the desired group chat.
• All group members will receive a push notification informing them of the call.
• Members can join the call by tapping “Join” in the notification, in the group chat, or in the chat overview.
• The group continues until the last participant has left the call.

Group calls are routed through a server, which obscures the IP address of the participants amongst one another. To make sure participants hear in real time what others are saying (i.e., the delay is as short as possible), media routers outside of Switzerland may be used. Learn more…

Completely disable Threema calls: Navigate to “Threema > Settings,” tap “Secure calls” (Android) or “Threema Calls” (iOS), and disable “Enable Threema Calls.”

If you disable Threema calls, no one can call you via Threema, and you can’t call anyone.

Don’t allow video calls: Navigate to “Threema > Settings,” tap “Secure calls” (Android) or “Threema Calls” (iOS), and disable “Allow Video Calls.”

If you don’t allow video calls, no one can send their video to you, and your can’t send anyone you video.

Don’t allow group calls: Navigate to “Threema > Settings,” tap “Secure calls” (Android) or “Threema Calls” (iOS), and disable “Enable Threema Group Calls.”

While a voice call is ongoing, approximately 750–800 KiB of data is transferred per minute.

The bit rate of video calls depends on the available bandwidth and the image quality.

If you hear your own voice as an echo during voice calls, the echo cancellation doesn’t work correctly on your call partner’s device, and the sound from the earpiece is sent back to you through the microphone.

Android: Please ask your call partner to change the Echo Cancellation in “About Threema > Advanced options” (from “Hardware echo cancellation” to “Software echo cancellation” or vice versa).

Ringing: The phone is ringing at the recipient’s end.

Busy: The recipient either rejected your call or is already talking on the phone to someone else.

Pickup: A connection has been established; you can talk to the callee.

Hangup: The connection was dropped.

Problem: The connection has been interrupted; an attempt to re-establish the connection is in progress.

The image quality of video calls depends on the available bandwidth and the settings of your call partner. In case of a poor network connection, the image quality is automatically lowered.

The preferred image quality can be adjusted in the Threema settings under “Secure calls > Preferred image quality” (Android) or “Threema Calls > Preferred Image Quality” (iOS). The following options are available:

• Balanced (Recommended): High image quality in Wi-Fi, reduced data consumption in the mobile network
• Low Data Consumption: Reduced image quality for lower data consumption
• Maximum Quality: Warning: This setting can cause considerable data consumption, also in the mobile network!

If you and your call partner prefer a different image quality, the lower quality will be used. If, for example, you have set “Maximum Quality” as preferred image quality, this image quality will only be used if your call partner has also set Maximum Quality as preferred image quality.

The quality of video calls depends on various factors. The most important factor is the available bandwidth of the caller and callee . If you experience problems with the transmission of the videos when conducting Threema calls, please connect both smartphones to a different network (e.g., to another Wi-Fi network or to the mobile network) for testing purposes.

On Android, media codecs might also cause problems. Media codecs are software components of your smartphone’s operating system that process incoming and outgoing video data streams and generate visible image sequences based on them.

In Threema, change the used codecs used in “Settings > About Threema > Advanced options > Video codecs.” Please use “Software codecs,” and test if the problem persists using this setting. The setting becomes active when conducting the next calls, it is not necessary to restart the app or your device. However, using software codecs can slightly increase your device’s energy consumption during video calls.

If this symptom occurs, either push notifications aren’t working properly on your contact’s phone, or there is a problem concerning background activity.

Please ask your contact to follow the troubleshooting instructions for Android (Samsung, Huawei, Xiaomi, Sony, OnePlus, Gigaset, Ulefone Armor, Doogee, etc.) or iOS.