About Traversal Using Relay NAT (TURN) Server

Both Acrobits Softphone and Groundwire support the TURN server feature. You may use TURN when encountering audio issues caused by the use of symmetric NAT in the network.

TURN is a protocol that allows network elements behind Network Address Translation (NAT) or a firewall to receive incoming data over Transport Control Protocol (TCP) or User Datagram Protocol (UDP) connections.

Audio Issues Caused by Symmetric NAT

Symmetric NAT is a network configuration often used on 3G networks and in other situations. However, it poses challenges for many SIP providers, especially when Session Traversal Utilities for NAT(STUN) do not work over symmetric NAT, leading to audio issues. To address these challenges, users using Acrobits Softphone and Groundwire on networks with symmetric NAT can employ TURN to enhance audio quality.

Using TURN

You need a TURN Server to use this feature. It is possible to run this server on your own, but most users may use a service.

  1. Upon signing up for a TURN server service, you receive the server address, username, and password.
  2. To open the desired SIP account in your Acrobits Softphone or Groundwire:
    • Android - Select Android Settings icon > Settings Accounts.
    • iOS - Open the Keypad tab, select iOS Setting icon > Accounts or SIP Accounts.
  3. Select Advanced Settings > NAT Traversal.
  4. Fill in the STUN Server, username, and password fields with the information obtained in step 1.
    On the NAT Traversal screen, Media is set to Auto (recommended) by default.
    Auto means TURN is only used when symmetric NAT is detected. However, some SIP providers may need to set it to Always.
  5. Select a check icon or Done to save the setting.


Using TURN may cause latency (audio delays) if the TURN server is located too far from you. For example, the numb server is located in Canada. Users in the U.S. and Canada work fine with this server, but not with users in other parts of the world.

We recommend you test with the numb server to check if TURN resolves your issue. If it helps, look for a TURN server closer to you if latency issues arise.