Who this is for: Every office using Cannon VoIP. It matters most for desk phones that use standard (unencrypted) call setup, but turning it off is safe for everyone.
What goes wrong
- You can hear the caller but they can't hear you, or the other way around (one-way audio).
- Calls drop at almost exactly 15 or 30 minutes.
- Transfers or holds fail, or the call goes silent after you take it off hold.
- Desk phones show as offline or stop ringing for incoming calls, then come back on their own.
Why it happens
SIP is the language phones use to set up a call. SIP ALG (Application Layer Gateway) is a router feature that tries to "help" by rewriting that traffic as it passes through.
Most routers do this badly. They change addresses in the call setup so the audio is sent to the wrong place, or they lose track of a call partway through.
How to fix it
- Sign in to your router or firewall's admin page. This is usually a web address like 192.168.1.1 printed on the router, or an app from the router maker.
- Look for a setting named SIP ALG, SIP Helper, SIP Transformations, SIP Passthrough or VoIP ALG.
- Turn it off (uncheck or set to Disabled).
- Save, then restart the router.
- Unplug each desk phone for 10 seconds and plug it back in so it reconnects cleanly.
Notes for common router types
- On most home and small office routers, look under Advanced, WAN Setup, NAT or Security.
- On most business firewalls, look under Advanced > VoIP, Firewall > Settings, or System > Advanced. Some firewalls have more than one SIP setting (for example a SIP helper and a SIP inspection rule). Turn off all of them.
- On some firewalls the setting only appears from the command line. If you can't find it, your IT person or the router maker's support can turn it off.
- If your internet provider supplied the router, the setting may be locked. Ask them to turn off SIP ALG, or to put their router in bridge mode and use your own router.
How to tell it worked
- Run the free Net Checker. It checks whether something on your network is changing call traffic.
- Make a test call longer than 30 minutes, put it on hold and take it off hold. Both sides should hear each other the whole time.
- Incoming calls ring every desk phone again without anyone restarting them.
Still having trouble? Contact Cannon VoIP support at 888-973-0515 or support@cannonvoip.com.
More router settings that affect call quality
- Set UDP Timeouts to at Least 300 Seconds
- Allow Cannon VoIP Through Your Firewall
- Fix Double NAT (Two Routers in a Row)
- Prioritize Voice Traffic with QoS
- Fix Bufferbloat with Smart Queue Management
- Stop Wi-Fi Band Steering and Roaming from Dropping Calls
- Guest and Isolated Wi-Fi Blocking the App
- DNS and Content Filtering Blocking Cannon VoIP
- VPNs and Security Software Interfering with Calls
- Mesh Wi-Fi Systems and Calls Cutting Out
- Wi-Fi Power Saving Causing Missed Calls
- Mobile Hotspots and Carrier-Grade NAT
See all router settings · What makes call quality good or bad