Fixing One-Way Audio and Dropped Registrations (SIP ALG and NAT)
If calls connect but you can't hear the other person (or they can't hear you), if incoming calls ring but go silent when answered, or if your phone keeps dropping its registration, the cause is almost always your router — specifically a feature called SIP ALG. This guide explains the fix.
Last reviewed: October 2026
What is SIP ALG and why does it cause problems?
SIP ALG (Application Layer Gateway) is a router feature meant to help phone calls get through NAT. There is no standard for it, so many routers rewrite the call setup messages incorrectly. The result is one-way audio, silence on answered calls, or phones that stop registering. It is often intermittent and clears for a while after a router restart, which makes it hard to pin down. Every VoIP provider recommends turning it off.
Fix 1: switch your phone to TLS (no router access needed)
TLS encrypts the call setup, so the router can't interfere with it. On your phone or PBX set:
- Server / proxy: sip.click2call.com.au
- Transport: TLS
- Port: 5061
If your device doesn't support TLS, use port 50600 instead of 5060 (sip.click2call.com.au:50600). Routers don't treat 50600 as a SIP port, so they leave it alone.
Fix 2: turn off SIP ALG on your router
Look in your router's settings under Advanced, WAN, NAT, Firewall or VoIP for "SIP ALG", "SIP Helper", "SIP Transformations" or "SIP passthrough", and turn it off. Restart the router and your phones afterwards. The exact steps depend on your router — your router's manual or manufacturer can tell you where the setting is. If you can't change the router, use Fix 1.
Fix 3: phones that keep dropping registration (NAT timeout)
Some routers forget a phone's connection after a short idle time, so incoming calls can't find it. If your router lets you set a UDP NAT timeout, set it to 60 seconds or more. Otherwise, set the phone's registration expiry (often "Registration Timeout" or "Expires") to 60 seconds so it checks in every minute and keeps the connection open. TLS and TCP also avoid this, because they hold the connection open.
Don't forward ports to your phone
You don't need port forwarding for Click2Call, and forwarding 5060 or 5061 to a phone or PBX exposes it to internet scanners (see Stopping Ghost and Spam Calls). Remove any such rules.
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