A dental practice switched to a cloud phone system in early 2025 and immediately had problems. Calls were choppy. Patients were hanging up. The front desk staff was frustrated.
Their internet was a 300 Mbps cable connection — more than enough bandwidth. The problem: during morning check-in rush, with 8 staff on calls simultaneously, the cable router was treating VoIP packets like any other traffic. Video streaming in the waiting room lobby was competing for bandwidth with incoming patient calls. No QoS. Variable latency. The phone system worked fine; the network wasn’t ready for it.
Two changes fixed it: basic QoS configuration on their router and a dedicated VLAN for voice traffic. No new internet contract required.
VoIP’s internet requirements are often misunderstood as purely a bandwidth question. They’re not.
The Four Requirements for VoIP Quality
1. Bandwidth (the easy one)
VoIP uses roughly 100 Kbps per concurrent call using standard G.711 codec. With overhead, budget 120–150 Kbps per line.
Quick calculation: 10 concurrent calls × 150 Kbps = 1.5 Mbps dedicated bandwidth needed for voice. This is bidirectional — you need 1.5 Mbps upload and 1.5 Mbps download.
HD voice codecs (G.722, Opus HD) require about 50–100% more: 200–300 Kbps per call. If your UCaaS provider supports HD voice, use the higher figure.
Bandwidth is rarely the bottleneck. Even a 50 Mbps connection has plenty of bandwidth for 30 simultaneous calls. The constraint is usually latency and QoS.
2. Latency (the critical one)
Latency is the time it takes for a packet to travel from your phone to the carrier’s server and back. VoIP is real-time — unlike a file download, you can’t buffer a phone conversation.
The ITU G.114 standard specifies:
- Under 150ms: Acceptable for most business calls
- Under 80ms: Good quality with no perceptible delay
- Over 150ms: Users notice the delay; conversations feel awkward
- Over 300ms: Calls become difficult to conduct normally
Run a latency test to your VoIP provider’s server from your office network. Your ISP’s general latency to internet destinations is a proxy, but test specifically to VoIP server IPs when possible.
Business fiber typically delivers 5–20ms to regional carrier infrastructure. Business cable typically delivers 15–40ms with occasional spikes. Both are acceptable; fiber is more consistent.
3. Jitter (the one nobody explains)
Jitter is variance in latency — when some packets take 20ms and others take 90ms. Your phone can compensate for some jitter using a jitter buffer (which adds a small intentional delay to smooth out variations), but excessive jitter causes choppy audio.
Acceptable jitter for VoIP: Under 30ms
Problematic jitter: Over 50ms consistently
Jitter shows up more on shared networks (cable during peak hours) than dedicated fiber connections. It’s also caused by WiFi — if your phones connect via WiFi, test signal quality. A phone on a weak WiFi signal 50 feet from the access point can have more jitter than the internet connection itself.
4. Packet Loss (the one that causes audio cuts)
Packet loss is the percentage of data packets that don’t arrive. VoIP is extremely sensitive to packet loss because there’s no time to retransmit missing packets in a real-time call.
Acceptable packet loss for VoIP: Under 1%
Noticeable impact: 1–3% causes occasional audio gaps
Unacceptable: Over 3% makes calls difficult to understand
Packet loss on business internet connections above 0.5% typically indicates a network problem (bad cable, overloaded router, congested segment) rather than an undersized plan.
QoS: The Configuration That Makes VoIP Work
Quality of Service (QoS) is router configuration that assigns priority to different types of traffic. VoIP packets marked as high-priority get bandwidth allocation before general web browsing, file downloads, or other traffic competing for the same connection.
Without QoS: when someone in the office starts a large file download or a video stream, VoIP traffic competes equally with that traffic. Latency spikes. Calls degrade.
With QoS: VoIP packets get first-in-line access. The large file download slows down slightly. The call quality stays consistent.
Most business-grade routers support QoS (Cisco Meraki, Fortinet, Peplink, Ubiquiti UniFi). Consumer routers often have limited or unreliable QoS. If you’re running VoIP through a consumer-grade router, that’s worth addressing before attributing call quality issues to your internet plan.
How to configure: Most UCaaS providers (RingCentral, 8×8, Teams Phone, Zoom Phone) publish recommended QoS settings including DSCP values for their traffic. Your IT team or MSP can implement these in under an hour on a compatible router.
What to Tell Your ISP Before You Switch
When contacting your ISP about supporting VoIP, ask specifically:
- “What is the average latency to [your VoIP provider]’s servers from my address?” Some ISPs have poor peering to specific destinations.
- “Does your business internet service support QoS tagging (DSCP markings)?” Most business-grade connections do; some consumer or entry-level business plans don’t honor DSCP.
- “What is your SLA for packet loss and jitter?” Business-grade SLAs typically specify maximum packet loss thresholds; residential-grade connections don’t.
- “Do you offer a dedicated voice circuit or managed VoIP plan?” Some providers offer separate voice-optimized connections.
Bandwidth Planning for VoIP
| Concurrent Calls | Bandwidth Required (G.711) | Bandwidth Required (HD Voice) |
|---|---|---|
| 5 | 0.75 Mbps | 1.5 Mbps |
| 10 | 1.5 Mbps | 3 Mbps |
| 20 | 3 Mbps | 6 Mbps |
| 50 | 7.5 Mbps | 15 Mbps |
Add this to your general internet bandwidth needs — VoIP runs on your shared internet connection unless you provision a dedicated circuit.
Pre-VoIP Internet Readiness Check
Before porting your phone numbers, run these tests:
- [ ] Latency test: Ping 8.8.8.8 and your UCaaS provider’s server. Should be under 80ms consistently.
- [ ] Jitter test: Use tools like PingPlotter or your UCaaS provider’s readiness tester. Under 20ms is good.
- [ ] Packet loss: Run a continuous ping for 5 minutes during business hours. Under 0.5% loss.
- [ ] Upload speed: During peak hours, confirm upload speed is at minimum 2× your calculated VoIP bandwidth need.
- [ ] QoS capability: Confirm your router supports QoS/DSCP priority marking.
- [ ] WiFi assessment: If phones will use WiFi, check signal strength and interference at deployment locations.
Most UCaaS providers have a readiness test tool — use it before your cutover date.
Frequently Asked Questions
What internet speed do I need for VoIP?
VoIP itself requires very little bandwidth: 100–150 Kbps per concurrent call. For a 10-line system with 8 concurrent calls, that’s about 1.2 Mbps. The internet speed you actually need is determined by everything else running on your network — VoIP adds a relatively small amount to your total bandwidth requirement.
Can I run VoIP on cable internet?
Yes — business cable internet works well for VoIP in most cases. Key requirements: latency under 150ms (cable typically delivers 15–40ms, acceptable), jitter under 30ms, and QoS configured to prioritize voice traffic. Cable’s asymmetric upload can be a concern if your upload is already heavily utilized by cloud sync or other services.
Why is my VoIP call quality bad even though I have fast internet?
Fast download speed doesn’t guarantee good VoIP quality. Check: (1) upload speed during peak hours, (2) latency to your UCaaS provider specifically, (3) jitter levels, (4) whether QoS is configured on your router, (5) whether VoIP phones are on WiFi with poor signal. Packet loss and latency issues are more likely culprits than insufficient bandwidth.
How many Mbps do I need for 10 VoIP lines?
Using standard G.711 codec: approximately 1.5 Mbps dedicated to voice for 10 concurrent calls. Using HD voice codecs: approximately 3 Mbps. In practice, budget 10× that headroom to ensure VoIP traffic doesn’t compete with other business traffic without QoS.
Does fiber internet improve VoIP quality?
Yes, primarily for three reasons: symmetric speeds eliminate upload bottlenecks, consistent latency with minimal jitter produces more stable call quality, and dedicated last-mile infrastructure eliminates congestion-related quality variability. For businesses running 20+ concurrent lines or sensitive voice applications, fiber is the recommended connection type.
Planning a switch to VoIP or UCaaS? Get a connectivity assessment to confirm your internet is ready before you port your numbers.
