How to Test for SIP ALG Interference

How to Test for SIP ALG Interference

SIP ALG can and usually does exist on routers, modems or in rare cases a managed switch. You must disable this feature for VentureTel's VoIP service to operate as expected on your network.

What is SIP ALG?

SIP ALG (Session Initiation Protocol Application Layer Gateway) is a feature found on some routers and firewalls that can interfere with the proper functioning of VoIP phone services like VentureTel. It can cause issues such as one-way audio, dropped calls, and registration problems.

Common Problems Caused by SIP ALG

  1. One-Way Audio: You may be able to hear the other party, but they can't hear you, or vice versa.
  2. Dropped Calls: Calls may disconnect unexpectedly.
  3. Registration Issues: Your VoIP phone might fail to register with the service, preventing you from making or receiving calls.
  4. Delayed Call Setup: You might experience a noticeable delay before the call connects and starts ringing.
  5. Poor Audio Quality: Audio might become distorted, choppy, or include strange artifacts.

Why Test for SIP ALG

If you're experiencing unexplained problems with your VentureTel VoIP phone service, it's recommended to test whether SIP ALG is the culprit.

How to Test for SIP ALG

  1. Visit the Visualware SIP ALG test page
    1. After the test, click the "VoIP" tab.
    2. In the lower white box, find the line "SIP ALG Firewall".
      1. If you see "Y": SIP ALG is active. You should disable it in your router/firewall settings.
      2. If you see "N": SIP ALG was not detected.
  2. Interpret the Results: The test will indicate whether SIP ALG is present on your network and potentially causing issues.
This web test simulates a single VoIP call using the G.711 codec. While it provides real-time analysis, remember that results might differ from real-world usage with multiple calls over a longer period.

If SIP ALG is Detected

  1. Disable SIP ALG: Refer to your router or firewall's documentation for instructions on how to disable SIP ALG. Most devices will have a setting specifically for this.
  2. VentureTel Support: If you're unable to disable SIP ALG or continue to have problems, contact VentureTel support for assistance.
Disabling SIP ALG can sometimes impact other network functions. If you have concerns, consult with a network professional or VentureTel support before making changes.

    • Related Articles

    • Disabling SIP ALG

      Disabling SIP-ALG is an essential part of setting QoS on a router and optimizing it for your VentureTel service. Many ALGs (including Cisco's) have bugs which cause call flow and registration failures. Some ALGs (including Cisco's) intermittently ...
    • Disable SIP ALG (SIP Helper) on Mikrotik Routers

      Mikrotik SIP ALG is called a SIP Helper and is located under /IP>Firewall>Service ports.  The SIP Helper feature must be disabled to properly allow VentureTel VoIP traffic to pass through the Mikrotik router.   To disable, run this command from the ...
    • Perform a simple VentureTel speed test

      Unfortunately, slow internet speeds, high packet loss, and even high latency in any network connection can quickly deteriorate not only the quality of VoIP calls, but even the overall service your business pays for. Take a look below to perform a ...
    • Adjusting Netgear Routers to Support VoIP

      Netgear ships their routers so that out of the box they rewrite SIP (VoIP) packets due to their stateful packet inspection (SPI) firewall & SIP ALG.  However, Netgerrs implementation of the SPI firewall and SIP ALG breaks the connection between VoIP ...
    • Configure Cisco RV325 for VoIP

      The default firewall settings on Cisco routers have SIP ALG and SPI (Stateful Packet Inspection) enabled, which can cause issues with cloud based VoIP.  ​ Firewall Configuration Go to System Summary and ensure that the firmware is up to date ...