Our estimates for a branch-office box on a small four-core mini PC: calls at once, memory and the line it needs.
"What do I buy for the branch?" is a fair question, and until now our answer was a shrug and "something small." Here are numbers.
The box we sized for
A fanless mini PC with a four-core Intel N100 processor: the kind that sits behind a monitor and draws a few watts.
A branch box does real work. Every call is converted for the trip to the main office and back, on a strict 20 millisecond beat. So the processor matters more than you might guess.
The estimates
| Engine on the box | The branch's phones | Comfortable calls at once | Flat out |
|---|---|---|---|
| Kahevo Rust Engine | Standard sound (G.711) | 130 to 200 | 270 to 430 |
| Kahevo Rust Engine | Wideband (G.722) | 90 to 140 | 180 to 280 |
| Kahevo Legacy | Standard sound (G.711) | 90 to 140 | 175 to 280 |
| Kahevo Legacy | Wideband (G.722) | 45 to 70 | 90 to 145 |
Comfortable means about half the processor, which is what keeps audio on time. Flat out is the whole processor: a ceiling, not a plan.
- Rust engine, standard sound
- Rust engine, wideband
- Legacy, standard sound
- Legacy, wideband
Memory
| Engine | Memory in use at a comfortable load | 4 GB box | 2 GB box |
|---|---|---|---|
| Kahevo Rust Engine | About 0.5 GB | Fine | Fine |
| Kahevo Legacy | 0.6 to 1 GB | Fine | Fine, with the runtime's memory capped |
Those figures include the operating system. Legacy uses more because its runtime keeps headroom for tidying up, not because calls hold more. On a 2 GB box, a setting in the service file caps it.
The line
At 100 calls at once, voice needs about 2.5 Mbit/s up and 3.5 Mbit/s down. A branch with ten people on the phone needs a tenth of that. Most branches run out of people long before they run out of line.
The honest part
These are estimates. We scaled them from our load test on a much faster desktop, by what is known of the two processors. We have not measured them on an N100 yet. When we have, this post gets a sequel with real figures, whichever way they fall.
What it means
A branch of twenty or thirty people is nowhere near any of these numbers. Buy the small box, pick 4 GB if you have the choice, switch on the Rust engine, and spend the difference on better headsets.