What internet IP telephony needs: speed, ping, jitter and a backup line
Sado AI team · · 4 min read
In short
IP telephony needs a steady connection more than a fast one. Each call at the same time takes about 100 kbit/s in each direction (G.711 codec), so four calls need around 1 Mbit/s with a margin. What matters more: delay (ping) under 150 ms, jitter under 30 ms, packet loss under 1%. Plug phones into cables, give voice priority on the router, move big uploads to the evening and get a backup line from a second provider. Test the line at the busiest hour with a long ping test.
What to measure: a table
| Measure | Target | How to check |
|---|---|---|
| Speed per call | About 100 kbit/s each way (G.711) | Calls at the same time × 100 kbit/s |
| Delay (ping) | Under 150 ms; usually under 50 ms to the provider’s server | Ping the provider’s server |
| Jitter, the swing in delay | Under 30 ms | A long ping: gap between the slowest and fastest reply |
| Packet loss | Under 1% | 100 pings: how many didn’t come back |
| Connection type | Cable; Wi-Fi only with priority | Check how the phone is connected |
A plain speed test shows only the first row. Sound quality usually depends on the next three.
How much speed: the estimate
Take the number of calls running at the same time at your busiest moment, multiply by 100 kbit/s and double it for a margin. For example, an office has 6 IP phones and at most 4 are in use at once: 4 × 100 = 400 kbit/s, so about 1 Mbit/s down and the same up with a margin. That is small for today’s office internet. The problem is rarely speed itself: video, cloud backups and file uploads share the same line and squeeze the voice out.
How to test your internet for calls
- Pick your busiest hour and test at exactly that time.
- Run a speed test and note the upload speed separately.
- Ask your provider for its SIP server address and send it 100 pings: count how many didn’t return and how much the times jump.
- Repeat while someone uploads a big file.
- Make a 10-minute test call at the busy hour and listen.
- If something is off: move phones to cables, turn on voice priority (QoS) on the router, move backups and uploads to the evening.
If the sound breaks up or calls drop, find the cause by symptom: call audio problems.
A backup line and power
- Get a backup connection from a second provider, and let the router switch to it on its own when the main one fails.
- A mobile (4G) modem is a good backup, but as the main line its delay jumps around.
- Put the router and switch on a UPS so IP phones stay on during a power cut.
- Turn off SIP ALG on the router unless your provider says otherwise.
For example, at the Shifo Dent clinic three reception phones ran on a 4G modem, and the sound lagged in the evenings. The clinic moved to fibre and kept the modem as a backup. This is only an example.
Office internet and an AI operator
If Sado’s AI operator is connected to your number directly through the provider, calls don’t pass through your office: they go from the provider straight to Sado. So even if the office internet goes down, the operator keeps answering. Office internet matters for your staff’s IP phones: when the operator transfers a call to someone, the sound depends on that phone’s connection.
More: AI operator for incoming calls, connecting your own number and questions about Sado. Try it live or call 78 778 01 23.
Questions
How many Mbit/s does IP telephony need?
About 100 kbit/s each way for every call running at the same time (G.711 codec). Four calls need around 1 Mbit/s with a margin. The usual problem isn’t speed but ping, jitter and packet loss.
Does IP telephony work over mobile internet (4G)?
Yes, but delay and jitter vary more than on a wired line. Use it as a backup, not as the main line.
Does an AI operator need fast office internet?
Not if the number is connected directly through the provider: calls don’t pass through the office. You need internet for your staff’s IP phones and to open the portal.