Broadband for VoIP and cloud phone systems

What VoIP asks of a broadband line

A voice over IP (VoIP) call does not need much bandwidth, but it is fussy about how that bandwidth arrives. Speech is cut into small packets and sent many times a second in both directions. If packets arrive late, out of order or not at all, people hear clipped words, robotic voices, echo or silence. The three things that cause it have names you will see on any voice test:

• Latency: how long a packet takes to cross the network. Too much and people talk over each other.
• Jitter: how much that delay varies from packet to packet. Phones buffer a little to smooth it out, but not much.
• Packet loss: packets that do not arrive. A small amount is audible.

Most of the time, these are caused not by the line being slow but by the line being full. A cloud backup, a large upload or several video meetings can fill the upload side of a broadband connection, and voice packets queue behind them. So the question for VoIP is less "how fast is my broadband?" and more "is there enough spare upload for calls at my busiest hour?"

How much bandwidth do business calls need?

Each provider publishes its own figure, and that is the one to plan with. For BT Cloud Voice, BT's rule of thumb is to allow at least 120 kbps of upload for every call you expect to be on at the same time, on top of your data, and to use no more than 80% of the connection for voice and data together. On that rule, ten simultaneous calls need about 1.2Mbps of spare upload. The full guidance, and BT's network assessment test, is on our sister site's BT Cloud Voice internet connection guide.

What usually decides whether calls are clear is the upload left over after everything else. These are the upload speeds BT quotes for its main tiers:

These are "up to" figures. BT's minimum speed guarantee is a download figure, so leave upload headroom rather than planning to the limit. A small team making a few calls at once on Standard Fibre is usually fine if nothing else is saturating the upload; an office that also backs up to the cloud, sends large files or runs video meetings all day benefits from BT Business Full Fibre and its higher upload. Our guide to what broadband speed your business needs helps you size the rest of the traffic.

Router settings that make or break call quality

Many call-quality problems come down to the router rather than the line. The settings to check:

• SIP ALG off. SIP ALG is a router feature that rewrites voice signalling as it passes through. With hosted phone services it usually causes one-way audio, dropped calls or phones that stop registering. BT's BT Cloud Voice guidance says its business hubs have SIP ALG switched off, though resetting a hub switches it back on; if you have reset the hub or use your own router, check it.
• Voice prioritised. Quality of service (QoS) settings let voice packets jump the queue ahead of downloads and backups. BT's BT Cloud Voice guidance says that on a BT connection it gives calls priority over other internet traffic. On BT Ultra Broadband, BT lists voice and video traffic prioritisation among the Cisco Meraki security appliance's features.
• Firewall rules. Hosted voice services need certain outbound ports open. A firewall that blocks them can stop phones registering or tests running.
• Your own router. BT allows a compatible router on BT Business Broadband, but BT's helpdesk does not support third-party routers, and BT says using your own router means losing Hybrid Backup and the Wi-Fi security features. See using your own router.

If calls are poor on a line that tests well, these settings are the first place to look, followed by the office network.

Wired phones, Wi-Fi and the office network

The connection to the building is only half the path. Inside, a few simple choices help:

• Cable desk phones where you can. A wired phone avoids Wi-Fi interference and congestion. BT's minimum specification for BT Cloud Voice asks for at least CAT5e structured cabling.
• Plan the ports. A broadband hub has a handful of network ports. Several desk phones usually need a network switch, and a power over Ethernet (PoE) switch can power phones that support it through the same cable.
• Wi-Fi for apps and softphones. Mobile apps and laptop softphones run over Wi-Fi, so coverage matters where people take calls. Complete Wi-Fi Plus, included with Pro, extends one network across the premises; see our business Wi-Fi guide.
• Keep guests off the voice path. Visitors belong on BT Guest Wi-Fi, which BT keeps separate and limits to a share of the available speed.

Backup, power cuts and emergency calls

If the broadband line fails, desk phones on that site cannot make or take calls unless there is a backup. If the power fails, the router, switch and phones go off too. Plan for both before you move your numbers.

• Hybrid Backup. BT's Hybrid Backup switches the connection to 4G automatically if the fixed line fails, and BT says static IP and IP voice services keep working while it does. It is included with Enhanced and Pro and is an add-on for Essential. BT backs it with its Always Connected Guarantee: under BT's terms, you may be eligible for compensation if Hybrid Backup fails to activate within 30 minutes of you reporting a fixed line fault.
• Ultra's built-in backup. On BT Ultra Broadband, cellular backup is part of the Cisco Meraki equipment rather than a separate add-on.
• Divert to mobiles. Most hosted phone services can send calls to a mobile or app when desk phones cannot be reached. Set this up before you need it.
• Power cuts. BT says that in a power cut you will not be able to make calls on a digital phone line. Keep a charged mobile to hand for emergency calls, and BT says extra support may be available if you do not have a mobile phone or are worried about calling the emergency services.

The PSTN switch-off guide covers the other devices that used to rely on a copper phone line, such as alarms and card machines.

Which BT plan suits a business on VoIP?

Any BT Business Broadband plan can carry VoIP calls. What changes from plan to plan is how well protected those calls are when something goes wrong.

For a small number of lines, BT's Digital Line (Cloud Voice Express) can be bundled with broadband on the non-Ultra plans: see BT Business Broadband and Phone and our sister site's guide to BT Cloud Voice Express. For a multi-user phone system with desk phones, apps and call routing, see BT Cloud Voice, which Forever Communications also supplies.

A checklist before you move your phones to VoIP

Work through these before the phones go live, not after the first complaint:

1. Count your busiest-hour calls, including the morning rush, and add anything else that runs at the same time: video meetings, backups, large uploads.
2. Test the line properly over a cable at a busy time. Our speed test guide explains how.
3. Run the provider's voice test. For BT Cloud Voice, BT's network assessment test has to be passed before ordering; it measures jitter, packet loss and the bandwidth usable for voice.
4. Check the router: SIP ALG off, voice prioritised, the required ports open.
5. Check the office network: cabling, switch ports and power for desk phones, and Wi-Fi where people use apps.
6. Plan backup and power: Hybrid Backup or Ultra's cellular backup, call diverts to mobiles, and what happens in a power cut.
7. List everything on your old phone line such as alarms, lifts, card machines and fax, and check each one. See BT Cloud Voice's guide to alarm and special lines.

How Forever Communications helps

We can look at the broadband and the phones together. We check what your address can get and the upload BT can offer there, recommend a plan with the right backup, and can add a BT Digital Line or BT Cloud Voice so the connection and the phones are planned as one.

Pricing for both is confirmed at quote. Contact us to talk about broadband for your phone system.