Most business networks can run VoIP well, but download speed isn’t the real test. Clear, reliable calls depend on low and steady delay (latency and jitter), almost no packet loss, enough upload capacity, and a router and firewall that don’t interfere with call traffic.
The good news is that voice uses very little bandwidth, and most problems come from a handful of fixable settings. This guide covers the numbers to aim for, what to check on your internet connection, office network and firewall, and a readiness checklist to work through before you switch.
Key takeaways
- Aim for one-way latency under 150 ms, average jitter under 30 ms and packet loss under 1%, ideally none.
- Each call on CloudLine uses less than 100 kbps each way, so upload congestion matters far more than raw speed.
- Prioritise voice with QoS, put phones on wired connections (ideally a voice VLAN), and turn off SIP ALG.
- Plan for outages with a mobile backup, call diversion and a UPS for your network gear.
- Secure the system: strong passwords, no exposed SIP ports and limits on international calling.
What do latency, jitter and packet loss mean for calls?
Latency is the time it takes your voice to reach the other person. The ITU-T’s G.114 recommendation says that if one-way delay stays below 150 ms, most applications, including speech, get essentially transparent interaction. It recommends not exceeding 400 ms for general network planning. Above that, people start talking over each other.
Jitter is variation in that delay. Voice travels as a steady stream of small packets, typically 50 per second. If they arrive unevenly, the phone’s jitter buffer smooths them out, but only up to a point. Cisco notes that jitter buffers are usually only effective on delay variations of less than 100 ms, and Cisco Press QoS design guidance targets average one-way jitter below 30 ms.
Packet loss is packets that never arrive. Cisco’s QoS for VoIP guide says that ideally there should be no packet loss for VoIP, and its design guidance puts the limit at 1%. Loss sounds like clipped words or robotic audio.
| Metric | Good | Acceptable | Poor |
|---|---|---|---|
| One-way latency | Under 150 ms | 150 to 400 ms (noticeable pauses) | Over 400 ms |
| Jitter (average) | Under 30 ms | Occasional spikes above 30 ms that the jitter buffer absorbs | Regularly above 30 ms, or spikes near 100 ms |
| Packet loss | 0% | Under 1%, not in bursts | 1% or more, or bursts of loss |
| Upload headroom | Plenty spare at peak times | Occasionally busy, with voice prioritised | Upload regularly maxed out |
One practical tip: many speed tests report “ping”, which is round-trip time. One-way latency is roughly half that. Test at busy times of day, not just first thing in the morning, and run a longer test if you can, because short tests miss intermittent problems.
How much bandwidth does VoIP need?
Less than most people expect. Each CloudLine call uses less than 100 kbps each way. How much a call uses depends on the codec, the method used to compress the audio:
- G.711 is standard phone-quality audio at 64 kbps. With network overheads, Cisco calculates about 87 kbps per call on Ethernet.
- G.722 is wideband or “HD voice”. The ITU standard provides 7 kHz audio within 64 kbps, so it sounds noticeably clearer for about the same bandwidth as G.711.
- G.729 compresses audio to 8 kbps, or about 31 kbps with overheads. It’s useful on very constrained links but doesn’t sound as natural as G.711 or G.722.
Ten simultaneous calls therefore need around 1 Mbps each way. The catch is upload. Most nbn plans are asymmetric: nbn’s Home Fast wholesale tier, for example, is 500 Mbps down but 50 Mbps up. A cloud backup, large file upload or several video meetings can fill the upload link, and that’s when calls break up. Capacity is rarely the problem. Contention is.
Setting up the office network: QoS, VLANs and wired connections
Prioritise voice with QoS
Quality of service (QoS) tells your switches and router to send voice packets first. The IETF’s RFC 4594 recommends marking VoIP with the EF (expedited forwarding) class, DSCP value 46. Most IP phones can mark their traffic this way.
The most important place for QoS is your router’s upload to the internet, because that’s where queues build up. Standard internet services generally don’t honour your markings once traffic leaves your network, so shape upload traffic slightly below your real upload speed and give voice priority within it.
Use a voice VLAN
A VLAN separates phones from computers on the same physical network. It makes QoS easier to apply, keeps broadcast traffic away from the phones and lets you set tighter security rules for voice. Managed switches can use LLDP-MED to tell phones which VLAN to join automatically. Our guide to PoE switches for IP phones covers this in more detail, along with powering phones over the network cable.
Wired or Wi-Fi?
Wired connections are more reliable for desk phones because they avoid interference and the drops that can happen when a device moves between access points. Wi-Fi is fine for the desktop and mobile apps if coverage is strong, but check signal in meeting rooms and at the edges of the office. If you need cordless handsets, DECT phones use their own radio band and don’t depend on Wi-Fi.
Firewall, SIP ALG and security
Many routers ship with a feature called SIP ALG that rewrites call signalling and commonly causes one-way audio, dropped calls and phones going offline. For most hosted and SIP trunk setups it should be off. Our guide to SIP ALG and how to turn it off covers the settings on common routers and firewalls, along with UDP timeouts and port ranges.
Security matters as much as quality. Toll fraud is when someone gains access to a phone system or SIP account and uses it to make calls, often to expensive international destinations, frequently after hours. To reduce the risk:
- Use long, unique passwords for every extension, SIP account and admin login, and change any defaults.
- Don’t forward SIP ports or expose the phone system’s admin page to the whole internet.
- Restrict access by country or IP address (geo-blocking) where your firewall supports it.
- Turn off international or premium-rate dialling for users who don’t need it.
- Keep router, firewall and phone firmware up to date.
Which nbn or internet service suits VoIP?
For a small office, a standard nbn plan with decent upload speed usually works well, provided upload isn’t saturated and voice is prioritised. If phones are critical to your business, look beyond speed at the service level. nbn offers enhanced service levels with faster fault restoration windows, arranged through your internet provider.
Larger or busier sites may suit nbn Enterprise Ethernet, which offers symmetrical speeds, a high-priority traffic class and 24/7 support, again bought through a service provider.
You may also hear about Priority Assistance. That’s a service for people with a life-threatening medical condition, which ACMA says only Telstra is required to offer. It isn’t a business fault-priority product, so for business continuity, ask your provider about enhanced service levels instead.
What happens if the internet or power goes down?
Every VoIP system depends on the internet connection, so plan for outages:
- Mobile backup. A router with 4G or 5G failover can keep calls running on a mobile connection when the nbn drops.
- Call diversion. With CloudLine’s hosted PBX, your team can keep taking calls on the mobile app over mobile data, and calls can divert to mobiles or another number.
- Power. nbn states that equipment connected via the nbn won’t work during a power outage. A UPS on your router, switch and nbn equipment covers short outages, and phones powered by a PoE switch on that UPS stay up too.
VoIP network readiness checklist
- Count how many people could be on calls at the same time, and allow under 100 kbps each way per call.
- Test latency, jitter and packet loss at busy times against the targets in the table above.
- Check your upload speed and what else uses it, such as backups, file sync and video meetings.
- Set up QoS on your router, especially for upload, and mark voice as EF.
- Connect desk phones by cable, and plan a voice VLAN if you have managed switches.
- Confirm how phones will be powered: PoE switch, injectors or power adapters.
- Turn off SIP ALG and check UDP timeouts on your router or firewall.
- Remove unnecessary port forwards, and secure admin logins and SIP passwords.
- Restrict international calling to those who need it.
- Plan for outages: mobile failover, call diversion and a UPS.
- Check Wi-Fi coverage wherever people will use the mobile or desktop app.
Can CloudLine check your network before you switch?
Yes, and we recommend it. CloudLine is part of an ISO 27001 certified IT company, so the same team that sets up your phones can look at the network and firewall they rely on. We check the router and firewall configuration, SIP ALG, QoS and security settings, and tell you plainly if anything needs to change before you move.
It applies whether you’re moving to our hosted PBX or connecting an existing phone system with SIP trunking. Mention it when you request a quote and we’ll include a network check in the plan.
Frequently asked questions
How many calls can my nbn connection handle?
In bandwidth terms, far more than most small businesses need, since each call uses less than 100 kbps each way. The real limit is how busy your upload is at peak times, so prioritise voice with QoS.
What is a good jitter for VoIP?
Aim for average jitter under 30 ms. Phones can smooth out occasional spikes, but regular jitter above that, or spikes approaching 100 ms, leads to choppy or robotic audio.
Does VoIP work over Wi-Fi?
Yes, especially for softphone and mobile apps, as long as coverage is strong. For desk phones, a wired connection is more reliable.
Do I need a new router for VoIP?
Not always. Many routers work well once SIP ALG is off and QoS is set up. If your router can’t do those things, or it’s an ISP-supplied model with locked settings, a business-grade router or firewall is worth considering.
Can VoIP run on a 4G or 5G connection?
It can, and a mobile connection makes a good backup. Mobile latency and jitter vary more than fixed lines, so it’s better as failover than as the main connection for a busy office.
Not sure whether your network is ready? Call 1800 256 830 or request a quote, and we’ll check your network and firewall before you switch.
