What is Jitter?
If your fibre line tests fast but video calls still freeze and games still rubber-band, jitter is almost always the culprit.
Jitter in plain English
Jitter is the variation in latency between data packets arriving at your device. If every ping is exactly 18 ms, jitter is 0. If pings bounce between 18 ms and 90 ms, you have ~72 ms of jitter - and that variability is what your video call, voice call or online game actually feels like.
You'll see jitter measured in milliseconds (ms). On a healthy SA fibre line jitter sits under 5 ms; anything above 30 ms will be audible in a voice call, and above 50 ms is usually unusable for live applications. Jitter and overall connection responsiveness track together - improving one usually improves the other.
Why jitter matters more than ping
A consistent 60 ms ping is fine for most things - your call sounds smooth, your game character moves predictably. But a ping that swings between 20 ms and 300 ms produces choppy audio, frozen video and unpredictable lag spikes, even though the average is the same 60 ms.
This matters because every real-time codec - Zoom's Opus, Microsoft Teams' Satin, Google Meet's WebRTC, Discord, FaceTime, every game's network layer - is built on a small jitter buffer. The codec holds the last 30-150 ms of audio in memory and plays it back evenly. When jitter exceeds the buffer, the codec runs out of audio to play, and you get the freeze you've heard a hundred times: "Sorry, you broke up there." It's almost never a download-speed problem; it's almost always jitter.
Two fibre lines with identical Ookla scores can feel completely different. The line with low jitter feels snappy; the one with high jitter feels broken.
What good jitter looks like on SA networks
Based on Ookla SA fixed-broadband intelligence, MyBroadband Insights and our own long-running speed-test data, these are the rough jitter bands you should expect by connection type during business hours:
- Vumatel Core / Openserve / Frogfoot fibre (idle): 1-4 ms jitter, 5-12 ms ping to a JHB / CPT test server. This is the floor you're paying for.
- Same fibre lines (peak hour, 19h-22h): 4-10 ms jitter, ping up 10-30%. Streaming and gaming households see this nightly; it's still well within comfortable limits.
- Cool Ideas, Webafrica, Afrihost on a clean line: Jitter is almost identical to the FNO baseline because all three peer heavily at NAPAfrica (see the next section). The ISP doesn't add meaningful jitter on a healthy line.
- 5G fixed-wireless (Rain, Vodacom Home 5G, MTN Home 5G): 8-20 ms jitter idle, 20-60 ms loaded. Usable for casual VoIP and most games, but noticeably worse than fibre.
- LTE fixed-wireless (Telkom SmartBroadband, Rain 4G, MTN Made For Home): 20-50 ms jitter idle, often 50-150 ms in peak hour as the local cell loads up. Not recommended as a primary line if you spend your days on calls.
- Legacy ADSL (last surviving lines): 20-80 ms jitter is common, worse on long copper runs. ADSL is being switched off - if you're still on it and your jitter is bad, that's the root cause.
If your fibre line is delivering peak-hour jitter above 20 ms, something is wrong - either inside your home (Wi-Fi, router, kinked patch) or upstream on the ISP. The troubleshooting steps further down isolate which.
What causes high jitter
Common causes on a home fibre line, in roughly the order we see them:
- Wi-Fi congestion. Too many devices on a 2.4 GHz channel, or overlapping channels with the neighbours. Wi-Fi adds 5-30 ms of jitter on top of whatever the line is doing, and is the single most common cause of "my fibre is bad" complaints.
- An overloaded line. Someone in the house pulling a Steam update or uploading a 4K video saturates the upload pipe; ACKs back up and every other packet's latency spikes. Most ISPs ship routers with no meaningful QoS by default, so a single hungry device punishes everyone.
- An old or under-spec router. The CPE Telkom shipped with ADSL lines (Huawei HG659, HG658, Mecer-branded TP-Link units) struggles to route gigabit fibre traffic - the NAT table fills, the CPU saturates, and jitter spikes under load. If your router is more than four years old, consider it suspect.
- ISP / FNO congestion at peak. 19h00-22h00 SA time is the national crunch. ISPs that have under-provisioned NAPAfrica peering see jitter rise sharply in this window, particularly to services like Showmax, DStv Stream, Netflix and YouTube SA caches.
- A faulty CPE or kinked fibre patch lead. The fibre between your ONT and the wall is fragile. Heat damage, sharp bends and bad SC/APC connectors all attenuate the signal, which the line card compensates for by retransmitting - visible as jitter and packet loss.
- International peering hops. Calls to a Zoom data centre in Frankfurt or Sydney inherit the variability of the undersea cable hops. Local jitter can be perfect while the international leg adds 20-40 ms - which is why jitter feels worse during international all-hands meetings than local calls.
The peering effect: NAPAfrica vs SAIX
Most jitter complaints on SA fibre are actually peering complaints. South Africa has two main paths for inter-network traffic:
- NAPAfrica - Teraco's neutral internet exchange, with points of presence in Johannesburg, Cape Town and Durban. It's free for members to peer at and carries the majority of SA-to-SA traffic in 2026. ISPs that peer well at NAPAfrica (Cool Ideas, Webafrica, Afrihost, RSAWEB, Vox, Mweb) deliver low jitter to other NAPAfrica-connected services - which is where Showmax, DStv Stream, MyBroadband, Takealot, the major SA banks and most local Netflix caches live.
- SAIX - Telkom's transit network. Historically the only option. ISPs that still route significant local traffic over SAIX rather than directly via NAPAfrica pay for that transit, and their customers' jitter to local services rises in peak hour when the SAIX transit gets congested.
This is the biggest single reason SA fibre ISP reviews disagree about which ISP is "best". On Cool Ideas, jitter to a JHB-hosted service routinely sits under 5 ms in peak hour because Cool Ideas peers extensively at NAPAfrica. On a smaller ISP with less direct peering, the same path can sit at 30 ms+ for the same hours. The cable to your house is identical; the path the packet takes after the FNO hand-off is not.
A practical test: open a terminal and run mtr showmax.com from your machine over a five-minute peak-hour window. If most of the jitter is in the first two hops you're seeing local-network or router problems; if it appears at hop three or four you're seeing your ISP's peering.
Router-specific fixes for the routers SA ISPs ship
The router is the most common single fix. Almost every SA fibre ISP ships one of four or five physical units; here's what we've seen work on each:
- Huawei HG8245H / HG8245W5 (Openserve ONT / router). The default Openserve unit. Disable the built-in 2.4 GHz radio if you have a separate Wi-Fi mesh; the Huawei radio is weak. Leave routing on it for now, or put it in bridge mode and PPPoE-dial from a downstream router. Firmware upgrades are pushed by Openserve OAM; you can't do them manually.
- Huawei HG659 (Telkom-era ADSL/VDSL). Showing its age. NAT table is small, Wi-Fi is 802.11ac wave 1, no MU-MIMO. If you're still using it on a fibre line, replace it - any TP-Link Archer AX23 or higher will outperform it for ~R900.
- ZTE F660 / F670L (Vumatel ONT). GPON ONT with built-in Wi-Fi. The Wi-Fi is mediocre; the routing is fine. Put it in bridge mode and use your own router for Wi-Fi - this alone drops jitter by 5-15 ms in most households.
- TP-Link Archer C6 / Archer AX10 (commonly supplied by Webafrica / Afrihost). Capable for the price, but defaults are not great. Enable Smart Connect, lock 5 GHz to channel 36 or 149, and turn off WMM Power Save - the last one helps jitter on iPhones and recent Androids.
- Mikrotik / Ubiquiti / Asus from a third-party install. If you're on one of these you usually don't need this section. Make sure Fast Track / Flow Offload is enabled if you're on a 500 Mbps+ line.
Regardless of router: prefer 5 GHz over 2.4 GHz for every device that supports it, keep the router off the floor and away from kitchen appliances, and run an Ethernet cable to any desktop or console that lives in one place.
Worked example: video call on Vumatel vs LTE
A 30-minute video call from the same house, on the same laptop, on two different connections, illustrates why jitter matters more than headline speed.
- Vumatel Core 100/100 Mbps, wired: Idle ping 7 ms, jitter 2 ms. Mid-call jitter peaks at 9 ms when a flatmate's laptop syncs OneDrive. Call audio is uninterrupted; the call peer reports "you sound perfect."
- LTE fallback (Rain 4G), same laptop, USB tether: Idle ping 32 ms, jitter 11 ms. Mid-call jitter spikes to 80-180 ms three times in the 30-minute window, each time corresponding to a cell-load transition (neighbours' phones hitting the same tower for school pick-up time). Audio drops out for 1-3 seconds on each spike; the call peer reports "you keep cutting out."
- Headline download on both: Vumatel 96 Mbps. LTE 38 Mbps. The LTE line is "fast enough" by every Mbps standard - but jitter alone makes it unusable for the actual job.
This is the gap that matters: speed is what the speed test shows; jitter is what you experience.
How to measure and fix it
- Run our jitter-aware speed test. Use our SA speed test and read the jitter result, not just download. Compare a wired test (laptop plugged into the router with Ethernet) against a Wi-Fi test from the same spot. A big gap means Wi-Fi; a small gap means the line.
- Reboot the router and ONT. Cliché, but routinely fixes a stuck NAT table or buffered radio firmware that's accumulated state. Power off for 30 seconds, then back on - in that order, ONT first.
- Switch to 5 GHz. 2.4 GHz is shared with microwaves, baby monitors, every neighbour's Wi-Fi and most IoT devices. 5 GHz has 25+ usable non-overlapping channels in SA and almost always halves your jitter on Wi-Fi.
- Run a wired test. If jitter is fine wired but bad on Wi-Fi, fix the Wi-Fi (router placement, mesh node, separate access point). If it's bad wired too, the problem is upstream.
- Call your ISP with concrete numbers. "My ping varies between 15 ms and 220 ms over a 5-minute test, wired, peak hour" gets you a level-2 engineer. "My internet is bad" gets you a level-1 script that ends with "have you tried turning it off and on again."
- If your ISP can't help, change ISP, not network. The FNO (Vumatel, Openserve, Frogfoot) is who owns the line - if the line itself is fine but your ISP's peering is bad, switch ISP. The fibre will be re-provisioned on the new ISP within 24-72 hours and the line stays in place. See our ISP reviews for peering quality scores.
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