How to Prepare Your Network for a VoIP Phone System Install

To prepare your network for a VoIP install, check you have enough upload and download bandwidth for your peak calls, a router and switch that can prioritise voice traffic, enough network ports and power for your handsets, and a firewall that allows your provider's traffic through. Then test the connection at your busiest time of day. Most call quality problems after a new install come from the network, not the phone system, so getting this right first saves a lot of troubleshooting later.

1. Check your internet speed and reliability

Start with what you're paying for and what you actually get. Run a speed test at your busiest time, not first thing in the morning, and note both download and upload speeds. Upload matters as much as download, because your voice travels in both directions at once.

As a rough guide, each call needs around 100 Kbps each way, but a realistic office needs far more once email, cloud software and video calls share the same line. Our guide to what internet speed you need for VoIP gives recommendations by office size, and our guide to VoIP bandwidth requirements shows how to work out the figure for your own peak calls.

If your connection is borderline, consider upgrading before the install. Our guide to FTTP vs a leased line helps you choose.

2. Work out how many calls you'll make at once

Bandwidth is driven by simultaneous calls, not headcount. Estimate your busiest hour, count how many calls are likely to be live at the same moment, and add a buffer of 20 to 30 per cent. That figure tells you how much capacity to reserve for voice.

3. Check your router and switch

Your router and switch are the heart of the network. Check that they:

• Support Quality of Service (QoS) so voice traffic can be prioritised over everything else
• Aren't overloaded or out of date. An old, underpowered router can struggle with voice traffic even on a fast connection
• Have enough ports for every wired handset, computer and access point
• Support PoE (Power over Ethernet) if you want to power handsets from the switch rather than from separate adapters

Our blog guide to optimising Quality of Service (QoS) for your VoIP system explains how to set it up.

4. Look at your cabling

Handsets need a decent network cable run back to the switch. Check the following:

• Cable quality. Cat5e or Cat6 is fine for voice. Old, damaged or very long cable runs cause dropouts
• Network points. Make sure there's a point at every desk where a handset will go
• Daisy-chaining. Many handsets have a second port so a computer can plug in through them. That works, but check it suits how your desks are laid out

5. Plan for power

Handsets need power from somewhere. PoE is the tidiest option, because one cable carries data and power, and it also lets you protect the whole system with a single battery backup. If you don't have PoE, each handset needs its own power adapter, which means more sockets and more clutter.

Remember that VoIP stops working in a power cut unless your router, switch and handsets are protected. Our guide to what happens to your phone system in a power cut covers backup options.

6. Consider Wi-Fi and cordless coverage

If staff use cordless handsets or softphones over Wi-Fi, check your coverage in every area where they'll take calls. Wi-Fi is more prone to interference and dropouts than a wired connection, so use ethernet wherever you can, particularly for anyone on calls all day.

For cordless DECT handsets, coverage works differently from Wi-Fi. Our guide to DECT repeaters explains when you need extra range, and our guide to softphone vs desk phone helps you decide who needs what.

7. Review your firewall and security settings

Firewalls sometimes block or interfere with voice traffic. Before the install:

• Ask your provider which ports and addresses they need open
• Check whether your router has a setting called SIP ALG, which often causes problems and is usually best switched off. Our guide to one-way audio explains why
• Check that any VPN or content filter doesn't interfere with call traffic

If you aren't sure, ask the person doing the install to review the firewall rather than guessing.

8. Separate voice from other traffic where you can

A separate virtual network (VLAN) for voice keeps call traffic apart from everything else, which cuts congestion and makes it easier to prioritise. It's not essential for a small office, but it's good practice for larger sites and anywhere call quality really matters.

9. Sort out your backup connection

A phone system that depends on a single internet line stops working when that line fails. Think about a backup before you go live, not after the first outage. Our guides to what happens when your internet goes down and setting up a failover connection explain the options.

10. Test before you go live

• Run a speed test at your busiest time of day
• Make test calls from the new system while the network is under normal load
• Check call quality in every part of the building
• Confirm numbers have been ported correctly. Our guide to how long porting takes helps you plan, and if you're coming off analogue or ISDN lines, our PSTN switch-off checklist shows the order to do things in

Network readiness checklist

• ☐ Speed test run at peak time, upload and download recorded
• ☐ Peak simultaneous calls estimated, with a buffer added
• ☐ Router supports QoS and isn't overloaded
• ☐ Switch has enough ports, and PoE if needed
• ☐ Cabling checked at every desk
• ☐ Power and battery backup planned
• ☐ Wi-Fi and DECT coverage checked
• ☐ Firewall reviewed and SIP ALG checked
• ☐ Backup connection planned
• ☐ Test calls made under normal load

Frequently asked questions

Do I need to upgrade my broadband before switching to VoIP? Not always. Many offices find their existing connection is enough once QoS is configured properly. Test it first, then decide.

Do I need a new router for VoIP? Only if your current one can't prioritise voice traffic, struggles under load or doesn't allow the settings your provider needs. Many business routers work well.

What is QoS and do I need it? Quality of Service tells your router to treat voice calls as a priority over other traffic. It's strongly recommended, because without it a large download or video call can make calls break up.

Is a separate VLAN for voice necessary? Not for a small office, but it's good practice for larger sites where call quality is critical.

Can I use Wi-Fi for desk phones? You can, but wired ethernet is more reliable. Use Wi-Fi where cabling isn't possible and check your coverage first.

Who should prepare the network, me or my provider? It's best done together. Your provider knows what the system needs, and whoever looks after your IT knows your network. A site survey before installation brings both together.

Getting the network right before installation is the single best thing you can do for call quality. Request a quote if you'd like T2K to survey your network before your install, or use our phone system finder to compare systems.