Call quality and troubleshooting · For 3CTel customers
Why do my VoIP calls drop or cut out?
VoIP calls drop for a small number of reasons: a router feature called SIP ALG that rewrites call signalling, a Wi-Fi or internet connection that briefly loses packets, or a firewall that closes the call's connection after a fixed time. A call that drops at the same point every time, such as 30 seconds or 15 minutes, almost always points to the router. Random drops usually point to the connection.
Step by step.
Note the pattern
Write down when calls drop: always at about the same time (30 seconds, 5 or 15 minutes), only on Wi-Fi devices, only on one phone, or at random. The pattern narrows the cause quickly.
Restart in order
Power off the modem, then the router, then the switch, then the phones. Turn them back on in the same order, waiting for each to come fully online. Many drops stop here.
Move to a cable
If the affected device is on Wi-Fi, connect it with an Ethernet cable and test again. If drops stop, the Wi-Fi is the problem, not the phone service.
Turn off SIP ALG
In the router settings, find SIP ALG (sometimes called SIP Helper or SIP Passthrough) and disable it. Restart the router and the phones. Consistent drops at a fixed time are the classic symptom.
Check the firewall session timeout
If drops still happen at a fixed interval, ask whoever manages the router or firewall to increase the UDP session timeout and confirm the phones' keep-alive interval is shorter than it.
Check bandwidth and QoS
Run a speed test during a busy period. If uploads are saturated by backups, cloud sync or video, enable QoS for voice traffic or schedule the heavy transfers.
Contact 3CTel
If drops continue, note the time, the number called and the device used, and contact support. Call logs on the service side show whether the call ended from your network or from the far end.
Fixed-time drops versus random drops
A call that ends at roughly the same point every time is not a quality problem; it is a signalling problem. Your phone and the 3CTel platform exchange short messages during a call to keep it alive. If a router's SIP ALG rewrites those messages, or a firewall closes the connection because it thinks the call is idle, the call is torn down cleanly at a predictable moment.
Random drops, often with a burst of poor audio just before, come from the connection: Wi-Fi interference, a congested upload, a modem that briefly resyncs, or an internet provider issue. The tests above separate the two.
Things that commonly cause drops
- SIP ALG enabled on a consumer or ISP-supplied router.
- Phones on 2.4 GHz Wi-Fi shared with dozens of other devices.
- Double NAT: a router behind an ISP modem that is also routing.
- A cloud backup or video upload saturating the upstream link.
- Two routers or firewalls each applying their own session timeouts.
- A cellular or satellite link with high, variable latency.
When to contact 3CTel
Contact support if drops continue after the restart, cable and SIP ALG checks, or if only calls to or from particular numbers drop. Include the date and time of two or three examples, the number called and the device used. The platform's call records show which side ended the call and help pinpoint whether the cause is your network, the carrier route, or the far end.
Related questions.
Why do calls drop at exactly 30 seconds?
A drop at about 30 seconds usually means the call was answered but the confirmation message never reached the phone, so the call is cancelled. SIP ALG on the router is the most common reason. Turning it off and restarting normally fixes it.
Do dropped calls mean my internet is too slow?
Rarely. A single call needs very little bandwidth. Drops come from instability, interference or router behaviour more often than from speed. A speed test that shows high jitter or packet loss is more telling than the download figure.
Can 3CTel see why a call dropped?
Support can see when each call started and ended and which side sent the end signal. That distinguishes a network or router issue at your site from a problem on the carrier route or at the other party.
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