...
Consumer routers may implement a feature known as SIP ALG (Application Layer Gateway). The primary purpose of SIP ALG is well-meaning: your router, with the feature enabled, attempts to scan and if necessary, modify, the VoIP data passing through it to ensure voice data is able to flow freely. While the intent is good, many implementations of SIP ALG by router manufacturers actually results in the exact opposite effect causing difficulties such as voice in one direction and calls not being received. Similarly, as router manufacturer implementation of SIP ALG can vary widely, the configuration of your home router in relation to your modem for internet connectivity and the provider of the service can also widely vary. By disabling SIP ALG on your router, you avoid further complicating the operation of your home network and the various types of data traveling in and out. In several, but not all cases, disabling SIP ALG on your home router can address handset reliability and call issues.
Recommended Consumer Routers
...
| Router Make | Router Model | Incompatibility Rationale/Problems |
|---|---|---|
| TP-Link | C7/C9 Archer (AC1750/AC1900, respectively) | No exposed SIP ALG toggling option in web interface |
| Apple | A1354 (4th Gen Airport Extreme) | No exposed SIP ALG setting, spottiness with handset stability |
| Apple | A1408 (5th Gen Airport Extreme) | No exposed SIP ALG setting, spottiness with handset stability |
| Apple | A1521 (6th Gen Airport Extreme) | No exposed SIP ALG setting, spottiness with handset stability |
| Comcast | DPC3939B | SIP ALG cannot be disabled, SIP traffic on port 5060 may be blocked, DNS may need to be manually set to Google DNS (8.8.8.8, 8.8.4.4) for Polycom handsets as temporary work around |
Manufacturer Specific Notes
...