Applies To:

Call2Teams - Customers


This article describes common audio issues and advises on how to resolve them.

Many of the options will rely on the latest Teams Connector. Ensure the user performing the diagnostics has the latest version installed.

Issue: Router Settings

Some routers have a SIP ALG (SIP Application Layer Gateway) setting that can adversely affect SIP VoIP calls.


SIP ALG is an application on many commercially available routers. It inspects and modifies VoIP traffic and packets in order to attempt to resolve firewall and NAT issues.

The SIP ALG application may re-write SIP messaging in order to allow the call to flow between the device and the SIP endpoint.

In modifying the SIP messages in the VoIP traffic, the SIP ALG application may render them unreadable. 

As a consequence, unexpected behaviour may occur, such as a SIP phone being unable to register, or call failure.

  • SIP ALG may break SIP signalling between the device and the SIP proxy.
  • If the SIP REGISTER or OPTIONS or NOTIFY messaging is modified by SIP ALG it may make the user unreachable, preventing inbound calls.
  • SIP ALG may also modify the SIP Call-ID header.


Users experiencing any of the issues described in this section should try disabling SIP ALG on their router. 

Methods will vary by make and model, the following is a list of common routers and suggested steps to disable SIP ALG:

  • Asus Routers

Disable the option SIP Passthrough under Advanced Settings / WAN -> NAT Passthrough.

If the router does not offer this then SIP ALG may be disabled via Telnet.

  • AVM Fritz!Box

SIP ALG can not be disabled.

  • Billion

Look for a SIP ALG option in the NAT or Firewall settings.

  • BT Homehub

SIP ALG can not be disabled.

  • BT Business Hub versions 3 and higher

SIP ALG can be disabled from the settings.

  • D-Link

In the 'Advanced' settings navigate to 'Application Level Gateway (ALG) Configuration' and un-tick the 'SIP' option.

  • DrayTek Vigor 2760

In the Network settings, navigate to NAT then ALG.

  • Draytek Vigor2750/Vigor2130/Other DrayTek devices

Use a telnet client:

  1. Open a command prompt
  2. Type in telnet and press the Enter key - Users may need to install the Telnet client on their device first.
  3. Enter the router logon credentials.
  4. Type in sys sip_alg 0 and press the Enter key 
  5. Type in sys commit and press the Enter key 

On Draytek Vigor2750 and Vigor2130 devices use these commands instead:

5. kmodule_ctl nf_nat_sip disable and press the Enter key

6. kmodule_ctl nf_conntrack_sip disable and press the Enter key

  • Huawei

The SIP ALG setting is usually found in the Security menu.

  • Linksys

Look for a SIP ALG option in the Administration tab under Advanced.

Users may also need to disable the SIP Firewall option.

  • Mikrotik

Disable SIP Helper.

  • Netgear

Look for a 'SIP ALG' checkbox in 'WAN' settings.

Port Scan and DoS Protection might also need to be disabled.

Disable STUN in the VoIP phone's settings.

  • SonicWALL Firewall

Under the VoIP tab, the option 'Enable Consistent NAT' should be enabled and 'Enable SIP Transformations' unchecked.  

  • Speedtouch

Telnet commands must be used to disable SIP ALG with some Speedtouch routers. Please refer to the manufacturer's support documentation.

  • Zyxel

Under Network or Advanced navigate to ALG and clear the options Enable SIP ALG and Enable SIP Transformations.

Telnet commands must be used to disable SIP ALG for some Zyxel routers. Please refer to the manufacturer's support documentation.

If users continue to experience call issues after disabling SIP ALG on their routers, they should check their firewall and NAT (Network Address Translation) configuration.

Issue: Incorrect Codec Selection

Incorrect or mismatched codecs can introduce audio issues in the call path. 

Where different legs of the call use different codecs, transcoding may be used to translate the media (audio), potentially resulting in a degradation of audio quality.


Restrict the codecs that the service uses in order to ensure compatibility with the customer's PBX/Trunk.

Users need to check which codecs are supported by their PBX/Trunk. These will vary by implementation.

The service uses carrier-grade Session Border Controllers which support a wide range of codecs.

Navigate to the PBX/Trunk Service page on the portal to configure the coded selection:

General Advice

Using the Microsoft Call Quality Dashboard

In the Microsoft Teams Admin Center users can log into the Microsoft Call Quality Dashboard. 

This supplies call quality information about the calls that go through Teams.  

For more information on how to setup and use the Microsoft Call Quality Dashboard see the following:

Preparing The Customer's Network for Teams

Please see this Microsoft article: Microsoft Teams - Preparing Your Network


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