If you are a Voice over Internet Protocol (VoIP) user, you may experience some occasional glitches and choppy sounds. These can be caused by many fixable issues, though one in particular stands out: the Session Initiation Protocol Application Layer Gateway (SIP ALG) feature that many routers have enabled by default.
SIP ALG is a feature found in most networked routers, and it’s designed to improve the quality of VoIP calls. More specifically, SIP ALG scans the data transmitted when making a VoIP and modifies it when necessary to avoid potential issues caused by firewalls (timed-out connections, unplanned downtime, firewall failure, etc.)
However, sometimes SIP ALG can cause more harm than good—such as by making changes to VoIP traffic that cause your calls to drop. This can happen if SIP ALG is not configured properly or is incompatible with your VoIP provider.
How SIP ALG Is Supposed To Work
SIP is what regulates data transfer sessions for things like Internet telephone calls, video calls, instant messaging, and multimedia conferencing. This protocol establishes communication sessions across various networks like the Internet, private IP networks, and cellular networks.
Since SIP ALG’s purpose is to examine and adjust VoIP call traffic to avoid firewall-related problems, SIP ALG should—in theory—make it easier for calls to connect across all networks because it can work around potential barriers to connection.
SIP ALG is also designed to improve SIP traffic by reducing latency, which is the time it takes for a packet of data to travel from one device to another. It accomplishes this by prioritizing SIP traffic and reducing the number of times the router processes it.
Thus, at face value, SIP ALG is a good idea from a security and functionality perspective.
The Potential Problem With SIP ALG
Problems arise when the security is too strict and causes breakdowns in connections.
This can happen in multiple ways:
- By incorrectly modifying SIP messages: This might lead to SIP devices having trouble talking to each other. For instance, SIP ALG might mess with the port numbers or remove necessary headers, causing some glitches.
- By interfering with the way that SIP devices negotiate NAT traversal: NAT traversal is how SIP devices can chat even when behind firewalls or NAT routers. If SIP ALG gets in the way of this, it might also lead to dropped calls or lower call quality.
- By lacking compatibility with some VoIP services: VoIP providers typically have their own particular ways of dealing with NAT traversal. If SIP ALG doesn’t mesh well with the VoIP provider’s methods, it can lead to issues, causing SIP calls to not go through.
SIP ALG can also hinder performance. For example, consumer routers that ISPs loan out to users often have limited memory, and packets can drop if the memory buffers overflow.
Signs That SIP ALG Is A Problem
Call issues happen for various reasons. But there are common symptoms that say SIP ALG is the culprit:
- One-way audio: Only one person can hear the other. This issue can happen consistently or come and go.
- Call drops: Calls suddenly cut off or drop after a brief connection.
- Audio quality issues: Poor audio quality, including choppy or distorted sound.
- Failed call setup: Facing trouble setting up a connection or dealing with delays during call initiation could suggest interference from SIP ALG.
- Call timeouts: Calls may time out or fail to connect altogether.
Of course, these symptoms are not exclusive to SIP ALG issues and can be caused by other factors as well, like a bad internet connection or device issues on the receiver’s side.
However, if you have not disabled SIP ALG, it’s worth considering it as a possible solution to your call issues.
How To Disable SIP ALG
The process for turning SIP ALG off may differ from router to router. Certain routers have a user-friendly web interface for this task, while others might require using command line prompts.
The steps for disabling SIP ALG will also vary depending on your router model, but the general process is the same.
The basic steps to disable the feature in a popular Netgear Router, for example, are as follows:
- Access the router’s web interface: Launch your web browser and input your router’s IP address into the address bar. This IP address is typically provided on the router or in its documentation. For many routers, the default IP address is either 192.168.1.1 or 192.168.0.1.
On the following page, you will be prompted to enter your router’s username and password. If you don’t know it, you can always try “admin” for both fields, but be sure to check any stickers on the modem or router hardware. If that doesn’t help, try calling your ISP for help with this step.
- Navigate to the SIP ALG settings: After logging into the router’s web interface, look for the Advanced or Advanced Settings section. Within this section, locate the WAN Setup or NAT settings. SIP ALG settings are often found within these sections.
- Disable SIP ALG: After pinpointing the SIP ALG settings, you will usually find an option to enable or disable it. In this instance, opt for disabling SIP ALG. The phrasing might differ based on the router’s interface, but it’s commonly labeled as SIP ALG, SIP Passthrough, or something similar.
- Save and reboot: Once you’ve disabled SIP ALG, don’t forget to save the alterations made to the router’s settings. Certain routers might require a restart to implement these changes effectively. It is advisable to reboot the router to ensure the complete deactivation of the SIP ALG feature.
Note that many ISP routers have hard-coded firmware that resets any customized settings after rebooting it. If your router has this factory configuration, simply do not reboot it. It’s still better than having SIP ALG enabled when it’s causing problems.
What to Do If You Can’t Disable SIP ALG
Very rarely, disabling SIP ALG isn’t an option. If this is the case for you, consider enabling Transport Layer Security (TLS).
TLS is a security protocol that’s designed to provide high-level communications security across computer networks. It can mask SIP signaling from ALG to ensure data packets aren’t altered and get sent correctly.
TLS is often configured at the application or server level rather than the router level. For example, if you use a VoIP service, you would configure TLS within the platform’s own user application.
Whether SIP ALG is enabled or not, TLS provides secure, quality communication.
Can Disabling SIP ALG Cause Problems?
Disabling SIP ALG has the potential to cause some trouble, but issues that arise from turning it off are both seldom and easy to undo.
If you turn off SIP ALG during troubleshooting for a VoIP problem, and it doesn’t work, you can simply turn it back on.
Disabling SIP ALG could also have unintended effects that may not be evident initially. For instance, it can hold back your router from effectively handling specific traffic, like traffic from security cameras or gaming consoles.
However, these problems are infrequent and can often be rectified by adjusting specific router settings, like the Quality of Service (QoS) configuration.
Overall, turning off SIP ALG carries little risk. Most of the time, disabling SIP ALG will not cause any issues, and it may even enhance the efficiency of your VoIP system.
When to Keep SIP ALG Enabled
Most VoIP providers recommend users disable SIP ALG because clearer connections are the result. But there are a couple of instances where it’s okay to keep SIP ALG enabled:
- If your VoIP system is working great with it on: There’s no reason to start messing with something that is working well for you. If your call quality is solid, no calls are dropping, you’re registering successfully, two-way audio is on point, and all your VoIP system’s features are working properly, leave it be. Don’t disable SIP ALG just because others are, or because a lot of literature says you should.
- Your VoIP service provider tells you to: Yes, many VoIP providers will tell you to disable SIP ALG. But if your provider tells you to keep it enabled for the sake of the system’s unique functionality, do so.
As mentioned above, if you want to test disabling SIP ALG, the risk of anything bad happening is relatively low. And you can always turn it back on as quickly as you turned it off.
What to Do If You’re Still Experiencing Problems After Disabling SIP ALG
You’ve disabled SIP ALG and you’re still having the issues mentioned above (one-way audio, call drops, audio quality issues, failed call setup, call timeouts). What should you do next?
- Check your firewall configuration: the defined set of security rules you’ve established could be blocking traffic that it shouldn’t, causing issues with SIP calls getting through.
- Contact your ISP or VoIP service provider: your internet service provider or your VoIP service provider may be able to give you additional insight into why you’re having the issues you’re having if SIP ALG isn’t the problem.
- Move to a cloud-based VoIP provider: SIP ALG isn’t necessary when using cloud-based VoIP systems.
- Get a new router: If all else fails, getting a new router can solve your issue.
