Telecoms glossary • K
Kbps (kilobits per second)
The unit VoIP bandwidth is quoted in. Useful mainly for working out how little of your line a phone system actually needs.
What is kbps?in networking and VoIP
1. Kbps means kilobits per second, a thousand bits of data every second. It is the unit VoIP consumption is quoted in: one call, one codec, so many kbps in each direction. Line speeds are quoted in Mbps, a thousand times larger, which is why a single call barely registers on a fibre connection.
2. Kbps is not kBps. Eight bits make a byte, so a 100 kbps stream moves about 12.5 kilobytes per second. Providers quote bits, file managers show bytes, and the factor of eight between them accounts for most arguments about whether a line is delivering what was sold.
What calls actually cost your line
Cisco’s per-call figures include the protocol headers, not just the audio, so they are the numbers to size a line against. Each one applies in both directions at once, and it is concurrent calls that matter, not how many people have a phone.
| Concurrent calls | G.711, each direction | G.729, each direction |
|---|---|---|
| 1 | 87 kbps | 31 kbps |
| 5 | 436 kbps | 156 kbps |
| 10 | 872 kbps | 312 kbps |
| 20 | 1.74 Mbps | 0.62 Mbps |
A twenty-seat office rarely exceeds six calls at once, so the honest figure for most South African small businesses is under a megabit in each direction. That is a rounding error on a fibre line and a real consideration on a contended wireless one.
Why a small number still matters
Voice does not need much capacity. It needs the capacity it has, continuously, without waiting behind anything else. A line with plenty of headroom on paper still produces broken calls when a cloud backup starts at 09:00, because the problem was never the total.
Two things follow. Size against the upstream figure rather than the headline download speed, since asymmetric lines give you far less of it. And treat QoS as part of the sizing rather than an optional extra, because prioritising a megabit of voice is what turns available bandwidth into usable bandwidth.
Sizing a line
Count concurrent calls, not extensions, and ask your provider for their per-call figure and whether it includes headers. A quote based on the raw codec rate understates real consumption by about a third.
About this entry
Definitions are written for South African business buyers and checked against primary sources – provider documentation, standards bodies and ICASA – not vendor marketing. Reviews are independent and sponsors are always disclosed. Read our editorial policy and scoring methodology.
Spotted something out of date, or think we have this wrong? Tell the editors and we will re-check it.