Fibre • VoIP call quality

Uncapped vs unshaped fibre: what actually protects your VoIP call quality

Q: Is unshaped or uncapped fibre better for VoIP?

Unshaped is better for call quality, because it stops your ISP de-prioritising real-time voice traffic. Uncapped only removes a data-volume limit and does nothing for quality. Ideally you want both, but if you can only prioritise one for voice, choose unshaped.

Q: Does uncapped fibre improve call quality?

No. Uncapped simply means no monthly data cap. Call quality is set by latency, jitter and packet loss, which shaping, an active fair usage policy and peak-hour contention affect – none of which "uncapped" addresses.

Q: What causes jitter and choppy audio on a fibre VoIP call?

Usually one of four things: the ISP shaping and de-prioritising voice, a fair usage policy throttling the line, peak-hour contention on a shared consumer line, or your own router treating voice like any other traffic. The fixes are an unshaped or dedicated line plus QoS on the router.

Q: How much upload speed does a VoIP call need?

About 100 kbps per concurrent call for the common G.711 codec once IP overhead is counted. Size your upload for the most simultaneous calls you will run and leave headroom. Symmetric fibre helps, because starved upload is a frequent cause of one-way audio.

Q: What latency and packet loss are acceptable for VoIP?

Aim for one-way mouth-to-ear delay at or under 150 ms (ITU-T G.114), jitter under 30 ms, and packet loss under 1%. Past those points the jitter buffer runs out and callers hear clipping, gaps or robotic audio.

Q: Do I need dedicated (uncontended) fibre for business calls?

Not always. A small team on a good unshaped consumer line with QoS is often fine. If you run many concurrent calls, staff a contact centre, or calls drive revenue, a business or dedicated line removes peak-hour contention and is worth the premium.

Q: How do I prioritise voice traffic on my fibre line?

Mark voice packets with DSCP EF (value 46), enable QoS on the router so voice is sent ahead of bulk traffic, and put phones on their own VLAN. Add an LTE or 5G failover so a line fault does not drop a live client call.

Uncapped is about how much data you get. Unshaped is about how your calls are treated on the way out. For business VoIP in South Africa, the second one is what keeps voices clear – here is why, and how to set the line up for voice.

Last verified 08 July 2026
By the WhichVoIP editorial team
9 min read

≤150 msOne-way delay for a clear call (ITU-T G.114)

~100 kbpsBandwidth one VoIP call needs (G.711)

<1%Packet loss before audio breaks up

<30 msJitter your line should hold under

The short answer

Do I need uncapped or unshaped fibre for good VoIP call quality?

For voice, unshaped matters more. Uncapped only removes a data-volume limit; it does nothing for call quality. An unshaped line stops your ISP de-prioritising real-time voice packets, which is what causes the jitter, packet loss and dropped calls buyers blame on “bad VoIP”. Buy for data if you like; buy unshaped for clear calls.

Max one-way delay for good voice (G.114)

Bandwidth per concurrent call (G.711)

Jitter ceiling for stable audio

Packet loss a call can absorb

A South African Professional On A Voip Headset Call At A Desk At Dusk — A call is real-time and unforgiving. A fibre line that looks fast on a speed test can still deliver choppy audio if it shapes or contends your voice packets at peak.

Uncapped, unshaped and unthrottled are three different promises

SA fibre marketing tends to lump these together under “fast internet”. They are not the same thing, and only some of them touch your calls.

Here is the clean split. Uncapped is a quantity promise: no monthly data limit. Unshaped is a quality promise: your ISP does not sort traffic into fast and slow lanes and push “non-priority” packets to the back of the queue. Unthrottled (no fair usage policy, or FUP) means your speed is not cut once you cross a usage threshold. A line can be uncapped and still shaped, or uncapped and still throttled after a FUP trigger – the labels are independent.

We bust the broader “uncapped equals unshaped” marketing myth in our fibre myths guide; this page is only about the piece that decides whether your calls are clear.

Line promise	What it actually controls	Why voice cares
Uncapped	Total data you may use per month	Barely – a call sips data
Unshaped	Whether voice packets are prioritised or de-prioritised	Critical – sets jitter and loss
No FUP / unthrottled	Whether speed is cut after a usage threshold	Matters once you are throttled
Dedicated (uncontended)	How many other premises share your upstream capacity	Decides peak-hour stability

How shaping, FUP and contention actually hit a call

Voice is the fussiest traffic on your line. A file download can wait a few milliseconds and re-send lost pieces; a live call cannot.

VoIP sends small voice packets over UDP with no re-transmission. Every packet has to arrive, in order, on time. When a line shapes traffic, an active FUP throttles it, or peak-hour contention fills the shared pipe, voice packets either arrive late and out of rhythm (jitter), or never arrive at all (packet loss). The jitter buffer papers over small variations, but past roughly 30 ms of jitter or 1% loss it runs out of room and you hear it: clipped words, robotic audio, gaps, one-way audio, or a dropped call.

The same event mathematically lowers your MOS – the mean opinion score that rates call quality from 1 to 5. The ITU-T E-model predicts MOS from delay, jitter and loss, so every millisecond of added delay and every dropped packet pushes the score down from toll quality toward “why does this sound terrible”.

What a shaped or contended line does to your voice packets

Watch the FUP. An “uncapped” line with a fair usage policy can throttle you to a fraction of your speed once a big backup or update crosses the threshold. Your calls degrade for the rest of the cycle even though nothing about the plan technically changed. See how these thresholds work in our fibre fair usage policy guide.

What good voice actually needs from the line

Voice does not need a big line. It needs a calm, consistent one. The numbers are small and specific.

A single G.711 call uses about 100 kbps once you add the IP, UDP and RTP overhead, so even ten concurrent calls fit inside 1 Mbps of headroom. What voice is sensitive to is timing, not volume. The engineering targets are well established:

✓

Aim for these on every call: one-way mouth-to-ear delay at or under 150 ms (ITU-T G.114), jitter under 30 ms, packet loss under 1%, and about 100 kbps of upload per concurrent call. Hit those and voice sounds toll-quality; miss them and no amount of raw speed fixes it.

Contention is the quiet killer

Here is the trap the “uncapped” label hides. Consumer fibre is contended – you share upstream capacity with many other premises, commonly at ratios around 1:20 to 1:50. At 21:00 when the neighbourhood streams, your line can be uncapped, unshaped and still congested, and calls wobble. A business or dedicated (uncontended) line reserves capacity for you, so peak hour looks like any other hour. If your team lives on calls, that guarantee is worth more than a bigger headline speed – we walk through where each fits in business fibre vs home fibre.

Uncapped tells you how much you can use. Unshaped tells you whether anyone will hear you clearly when you use it.

WhichVoIP editorial view

Configure your fibre line for reliable voice

Picking the right line is half the job. The other half is making sure voice gets treated as voice once the traffic reaches your own equipment.

Choose unshaped first, dedicated if calls are the businessAn unshaped line is the baseline. Call-heavy teams, contact centres or offices with many concurrent calls should move to a business or dedicated (uncontended) line. Our business fibre package guide covers how to size the tier.

Size the upload for peak concurrent callsCount the most calls you will ever run at once, multiply by ~100 kbps, and leave headroom. Symmetric fibre (equal upload and download) is worth paying for, because a starved upload path is a common cause of one-way audio.

Tag voice and turn on QoS at the routerMark voice packets with DSCP EF (value 46) and enable QoS so the router sends them ahead of bulk traffic. This protects calls the moment a big upload or backup competes for the same line.

Separate voice from everyday trafficPut phones and softphones on their own VLAN or network segment so a busy office LAN does not add its own jitter on top of whatever the ISP is doing.

Add a failover pathAn LTE or 5G backup keeps calls up when the fibre link faults. Combined with a small UPS on the router and ONT, it keeps the front desk answering through a power interruption too.

A Tidy Small-Office Fibre Router, Ont And Network Switch Mounted On A Wall — Most call-quality wins live on your own equipment: prioritise voice with QoS, keep it on its own segment, and add a failover path.

Our verdict

If you are choosing a fibre line to run business calls on, unshaped is the non-negotiable and uncapped is a convenience. Uncapped keeps you from running out of data; unshaped keeps your voice out of the slow lane. For a small team, a good unshaped consumer line with QoS configured is often enough. For call-heavy operations, pay for a business or dedicated line so peak-hour contention never touches a client call.

Our recommendation: shortlist unshaped lines, confirm the FUP and contention terms in writing, then set DSCP EF and QoS on your router. If calls are core to revenue, go dedicated and add LTE or 5G failover.

Get fibre that keeps your calls clear

Tell us how many people call at once and we will line up business fibre and VoIP quotes built for voice, not just for speed tests.

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Frequently asked questions

Is unshaped or uncapped fibre better for VoIP?

Unshaped is better for call quality, because it stops your ISP de-prioritising real-time voice traffic. Uncapped only removes a data-volume limit and does nothing for quality. Ideally you want both, but if you can only prioritise one for voice, choose unshaped.

Does uncapped fibre improve call quality?

No. Uncapped simply means no monthly data cap. Call quality is set by latency, jitter and packet loss, which shaping, an active fair usage policy and peak-hour contention affect – none of which “uncapped” addresses.

What causes jitter and choppy audio on a fibre VoIP call?

Usually one of four things: the ISP shaping and de-prioritising voice, a fair usage policy throttling the line, peak-hour contention on a shared consumer line, or your own router treating voice like any other traffic. The fixes are an unshaped or dedicated line plus QoS on the router.

How much upload speed does a VoIP call need?

About 100 kbps per concurrent call for the common G.711 codec once IP overhead is counted. Size your upload for the most simultaneous calls you will run and leave headroom. Symmetric fibre helps, because starved upload is a frequent cause of one-way audio.

What latency and packet loss are acceptable for VoIP?

Aim for one-way mouth-to-ear delay at or under 150 ms (ITU-T G.114), jitter under 30 ms, and packet loss under 1%. Past those points the jitter buffer runs out and callers hear clipping, gaps or robotic audio.

Do I need dedicated (uncontended) fibre for business calls?

Not always. A small team on a good unshaped consumer line with QoS is often fine. If you run many concurrent calls, staff a contact centre, or calls drive revenue, a business or dedicated line removes peak-hour contention and is worth the premium.

How do I prioritise voice traffic on my fibre line?