VoIP and SIP tools for people who keep the phones working
Look up a SIP error in seconds, size your internet link for voice, and estimate call quality from your network stats. Built for VoIP engineers, IT admins and contact centre teams.
Tools
SIP Response Codes
Every SIP status code from 100 to 608, with plain-English meanings, common causes and fixes.
VoIP Bandwidth Calculator
Bandwidth per call and for your whole office, for G.711, G.729, Opus and more, including all overhead.
MOS Call Quality Estimator
Estimate MOS and R-factor from latency, jitter, packet loss and codec, with tips to fix bad calls.
Most-searched SIP errors
Guides
How Much Bandwidth Does VoIP Need?
Per-call VoIP bandwidth for G.711, G.729, G.722 and Opus, including IP, UDP, RTP and Ethernet overhead, plus how to size an office internet link.
GuideHow to Fix One-Way Audio on VoIP Calls
One side can't hear the other? A step-by-step guide to fixing one-way and no-audio VoIP calls caused by NAT, SIP ALG, firewalls and wrong SDP addresses.
GuideWhat Is MOS? VoIP Call Quality Explained
MOS and R-factor explained: what the call quality scores mean, how latency, jitter, packet loss and codecs affect them, and what targets to aim for.
GuideSIP ALG: What It Is and Why to Disable It
What SIP ALG does, why it breaks VoIP calls and registrations, how to tell if it's causing problems, and how to turn it off on common routers and firewalls.
Frequently asked questions
Are these tools free?
Yes. Every tool and reference on this site is free, with no account or sign-up needed. Calculations run in your browser.
How accurate are the calculators?
The bandwidth calculator uses the standard packet-size method (payload plus RTP, UDP, IP and layer-2 headers). The MOS estimator uses a simplified ITU-T G.107 E-model, which is good for planning and comparison. For exact figures, measure real calls with your monitoring tools.
Can I share my results?
Yes. The calculators save your inputs in the page address, so you can copy the link and send it to a colleague or paste it into a ticket.