SIP ALG modifies VoIP traffic (packets) and is enabled by default on many routers. When implemented correctly, SIP ALG modifies specific IP addresses in these packets, changing them from your local IP address to your public IP address. Unfortunately, in many routers it is poorly implemented and, instead of replacing only the specific IP addresses that need to be replaced, it replaces all of them, which then breaks SIP signalling. This poor implementation of SIP ALG can cause several issues, such as:
- Calls dropping after a set period of time
- Calls dropping when trying to retrieve the call from hold
- Calls dropping when being transferred
- Calls not being received
- Unable to make outbound calls
- Calls with no audio
- Calls with one way audio
- Other extensions continue ringing after a call has been answered
Not all routers offer the option to disable SIP ALG, some of the most popular routers are listed below.
|Can Disable SIP ALG||Can Not Disable SIP ALG|
|Technicolor, Thomson, SpeedTouch||D-Link DIR-655|
|Netgear||BT Home Hub|
|Juniper / Netscreen SSG Series||Virgin Media Super Hub|
|Cisco 800 Series|
This list is not extensive, so if your router is not listed here, try typing the make and model of your router, followed by the phrase disable SIP ALG, into Google.
Best Solution: Disable SIP ALG On Router
Alternative Solution: Change VoIP Phone Ports
- Sip Server: sip.sipcentric.com:5065
- Local SIP Port: 5065
- Proxy Server Port (If using a proxy): 5065
NB: If you are using multiple accounts on the same phone, ensure that you don't use the same Local SIP Port on multiple accounts. Each account must have a unique Local SIP Port. We recommend using 5065 for the first, 5066 for the second, and so forth.