Most VoIP problems on office networks come from the router: a feature called SIP ALG rewriting call traffic, connection timeouts that close calls after a set time, or no priority for voice traffic. Turning off SIP ALG and enabling quality-of-service fixes most cases.
Common causes
SIP ALG on the router
This router feature tries to help VoIP but often breaks it, causing one-way audio and dropped calls.
NAT or UDP timeouts
If calls drop at the same length (often 15 or 30 minutes), the router is closing the connection.
No priority for voice
Downloads and uploads compete with calls, causing choppy audio.
Packet loss or jitter
Line or WiFi problems damage call quality even when the internet seems fine.
Phones on WiFi or a busy network
Desk phones work best wired, ideally on their own VLAN.
How to fix it, step by step
- 1
Turn off SIP ALG
Find SIP ALG (sometimes called SIP helper or SIP passthrough) in the router settings and disable it, then reboot the phones.
- 2
Check for timed drops
If calls drop at an exact duration, increase the router's UDP timeout or follow the phone provider's settings.
- 3
Enable quality of service
Give voice traffic priority so it isn't affected by other activity.
- 4
Wire the phones
Connect desk phones by cable, ideally on a PoE switch so they don't need power adapters.
- 5
Test for packet loss
Ping your phone provider's servers and check for loss and jitter during busy times.
When to call a technician
VoIP issues often bounce between the phone provider and whoever manages the network. We configure the router, switches, and QoS to your phone provider's requirements and test calls until they're stable.
On-site support across Orange County · see our business networking and WiFi installation services.
Frequently asked questions
What is SIP ALG?
It's a router feature that modifies VoIP traffic. Most VoIP providers recommend turning it off because it causes more problems than it solves.
Why do calls drop after exactly 15 minutes?
That's usually a router timeout closing the call's connection. Adjusting the timeout or disabling SIP ALG typically fixes it.
Should VoIP phones be on their own network?
In larger offices, a separate voice VLAN with priority keeps call quality steady and simplifies troubleshooting.