Known Issues With SIP ALG
SIP Application-Level Gateway (ALG) is a setting on routers and firewalls which enables them to be a translator between the phones and SIP servers (SureTel servers). When enabled, each SIP packet is intercepted and re-written. We recommend disabling this feature as it will often create intermittent issues, such as the following
- Calls are dropped
- Calls cannot connect
- One way call traffic
- Ghost/fake calls
It should be noted that a network can have SIP ALG enabled and the phones may work fine for a month, a year, or more before experiencing any issues.
Please reach out to your router or firewall manufacturer for instructions on how to disable SIP ALG. If the it does not have the option to disable SIP ALG, then it is recommended that the it be replaced with one that does.