Telecoms glossary • L
Latency
The gap between speaking and being heard. Small enough and nobody notices; large enough and both people keep interrupting each other.
What is latency?in VoIP and business telephony
1. Latency is the one-way delay between a word leaving your mouth and reaching the other person’s ear. It is measured in milliseconds and it accumulates at every stage of the journey: the codec, the network, the buffer at the far end and the handset itself. Past roughly 150 ms, conversation starts to break down.
2. Latency is not ping. A ping measures a round trip to a single server and reports it as one number. Call latency is one way, end to end, and includes the delay every device adds before a packet reaches the network at all.
What each band actually feels like
ITU-T G.114, the standard everyone quotes without naming, divides one-way delay into three zones. It is worth reading them as descriptions of a conversation rather than as pass or fail marks.
| One-way delay | What G.114 says | What it sounds like on a call |
|---|---|---|
| Below 150 ms | Essentially transparent interactivity | Nobody thinks about the line. Interruptions and short answers land where they were aimed. |
| 150 to 400 ms | Degrades progressively; not recommended to exceed 400 ms in planning | Both people start talking over each other, then start pausing to compensate. Tiring rather than unusable. |
| Above 400 ms | Unacceptable for general network planning | Radio-style conversation. People wait for the other side to finish before replying. |
Cisco’s design guidance takes the same 150 ms as its target for mouth-to-ear delay, alongside under 30 ms of jitter and no more than 1% packet loss. Those three numbers travel together and should be quoted together.
South African networks sit comfortably inside the first band for local calls. MyBroadband’s Q1 2025 fibre testing, measured to servers inside Teraco, put the best providers under 10 ms, and its Q2 2026 mobile report put the four national networks between 28 and 41 ms. Latency is rarely the fault on a local call. It becomes the fault the moment the call leaves the country.
Where the milliseconds come from
Delay is cumulative, and the parts you can change are not the parts most people reach for first.
- Distance
- Light in fibre covers roughly 200 km every millisecond. Johannesburg to Cape Town is about 1,260 km, so around 6 ms one way before a single device touches the packet. An intercontinental leg costs an order of magnitude more, which is the whole argument for a platform that terminates calls in South Africa.
- Queueing
- Every interface a packet crosses can hold it behind other traffic. This is the portion QoS reclaims, and on a busy office line it is usually the largest controllable share.
- The codec
- Sampling, packetising and rebuilding audio take time at both ends. A standard 20 ms sample is charged twice, and compressed codecs add more processing than uncompressed ones.
- The jitter buffer
- Holding packets to smooth uneven arrival is delay by design. A network with bad jitter forces a deeper buffer, so jitter and latency get worse together rather than independently.
Routing is the one to check first on an international-sounding call. A local number answered by a platform hosted overseas pays the distance twice, once each way, and no amount of office network tuning recovers it.
What you can fix, and what you cannot
Split the problem before spending anything.
- Worth doing
- Prioritise voice on the router so packets stop queueing behind backups and uploads. Cable the desk phones rather than running them over Wi-Fi. Choose a provider whose platform and interconnect sit in South Africa. Check whether a VPN or a cloud security service is sending your voice traffic on a detour.
- Not worth doing
- Buying more bandwidth to fix delay on a line that is not saturated. A bigger pipe does not shorten the road. Shrinking the jitter buffer helps only if jitter is already low, and makes audio choppy if it is not.
- Cannot be fixed
- Physical distance, an overseas leg you did not choose, and satellite paths. These are answered by moving the call, not by tuning it.
Echo is a different fault
People report latency when they hear themselves a moment after speaking. Delay makes echo noticeable, but it does not create it. The echo comes from a hybrid on an analogue leg or from a handset speaker feeding back into its own microphone, and the answer is echo cancellation or a headset, not a faster line.
The test is simple. If the other party hears the echo and you do not, the loop is at their end. If a delay exists but neither side hears a repeat of their own voice, you have latency and nothing else.
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.
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